Ecology of the Subarctic Regions: Proceedings of the Helsinki Symposium

Ecology of the subarctic regions

Écologie des régions subarctiques

Proceedings of the Helsinki symposium

Actes du colloque d’Helsinki

,

%

unesco

Ecology a n d conservation / Écologie et conservation

Titles in this series

/ Dans

cette collection

1

I.

Ecology of the subarctic regions. Proceedings of the Helsinki symposium &cologie des régions subarctiques. Actes du colloque d’Helsinki

II.

Methods of study in soil ecology. Proceedings of the Paris symposium Méthodes d’étude de l’écologie des sols. Acies du colloque de Paris

III.

Resources of the Biosphere. Proceeding of the Paris Conference (in preparation)

1

PubIished in 1970 by the United Nations Educational, Scientific and Cultural Organization Place de Fontenoy, 75 P a r i ~ - 7 ~ Printed by Imprimeries Réunies de Chambéry Publié en 1970 par l'organisation des Nations Unies pour l'éducation, la science et la culture place de Fontenoy, 75 Paris-7e Imprimeries Réunies de Chambéry

0 Unesco

1970 Printed in France

SC.SS/XXIV. 1/AF

Preface

The promotion of research in plant and animal ecology has been the objective of m a n y symposia organized or sponsored by Unesco and is one of the main fields of research towards which the Organization directs its attention in relation to its activities in natural resources research. While previous work has been concentrated on problems in the arid zone and in the humid tropics, the present volume is devoted to a completely different environment: the subarctic environment. The area of transition between the temperate zone and the Arctic tundra,comprising tracts of forest,fen and heathland in north-western Canada, Alaska, northern Scandinavia, northern Russia and Siberia, was the subject of a symposium organized by the Government of Finland and Unesco in co-operation with the International Geographical Union. It was held in Otaniemi (near Helsinki) from 25 July to 3 August 1966,and was attended by 70 scientists from 13 countries. The opening speeches were given by the Finnish Minister of Education,Mr.R.H.Oittinen and by Professor Paavo Kallio, of the University of Turku. The papers presented were divided into nine sections : subarctic definition; meteorology of subarctic regions; snow cover as an ecologicalfactor;weathering and geomorphological processes; permafrost as an ecological factor; main features of soil-forming processes; ecology of subarctic vegetation; ecology of important species of the subarctic fauna; conservation of nature and rational use of renewable natural resources of subarctic regions. It is hoped that the publication of these papers will lead to a better understanding of the physical conditions of the regions under study and will open up n e w perspectives for further research and practical applications. M a n y of the papers which were the result of highly specialized research were presented in a w a y

Préface

L a promotion de la recherche concernant l’écologie végétale et animale a fait l’objet d’un grand nombre de colloques organisés OU patronnés par l’Unesco, et c’est un des principaux domaines de la recherche dont s’occupe l’organisation dans le cadre de ses activités relatives aux ressources naturelles. Les travaux antérieurs ont porté essentiellement sur les problèmes de la zone aride et de la zone tropicale humide, mais le présent volume est consacré à un milieu entièrement différent: celui des régions subarctiques. L a région intermédiaire qui est située entre la zone tempérée et la toundra arctique et qui comprend des forêts, des marécages et des landes (nord-ouest du Canada, Alaska, Scandinavie septentrionale,nord de la Russie et Sibérie) a fait l’objet d’un colloque organisé par le gouvernement finlandais et l’Unesco, en coopération avec l’Union géographique internationale. Ce colloque s’est tenu à Otaniemi (près d’Helsinki) du 25 juillet au 3 août 1966 et a réuni soixante-dix savants de treize pays. Les discours d’ouverture ont été prononcés par le ministre finlandais de l’éducation, M. R.H.Oittinen, et par le professeur Paavo Kallio, de l’université de Turku. Les mémoires qui ont été présentés étaient répartis en neuf sections: définition de la zone subarctique; météorologie des régions subarctiques;le tapis neigeux en tant que facteur écologique; phénomènes météorologiques et géomorphologiques; le pergélisol en tant que facteur écologique; principaux aspects des phénomènes de formation du sol; écologie de la végétation subarctique; écologie des espèces importantes de la faune subarctique; conservation de la nature et utilisation rationnelle des ressources naturelles renouvelables des régions subarctiques. On espère que la publication de ces mémoires contribuera à faire mieux comprendre les conditions physiques des régions étudiées et ouvrira de nouvelles perspectives en ce qui concerne la recherche et les

such as to arouse interest a m o n g colleagues working

applications pratiques. Un grand n o m b r e de mémoires,

in entirely different fields.

qui étaient l’aboutissement de recherches hautement

A m o n g the major points arising from the discussions were the need for the establishment of protected control areas ; for international treaties protecting migratory birds, whales, seals, etc., a n d for a better understanding of cyclic fluctuations of subarctic m a m m a l s and birds, the prime problem of boreal terrestrial ecology. T h e meeting urged that research should be carried out o n productivity a n d sustained yield of subarctic fauna a n d flora and that meteorological observations b e extended and improved for microclimatological studies in the subarctic zones. Following the presentation of papers a n d the discussions a visit w a s arranged to the University of Turku, and a four-day field excursion to Lapland to visit the K e v o Research Station. An alternative field excursion w a s arranged for zoologists to the Oulanka Biological Station of the University of Oulu. In presenting this volume, Unesco wishes to offer its thanks to the participants in the s y m p o s i u m whose papers have m a d e it possible, and to Professor Kallio a n d the m e m b e r s of the Finnish organizing committee for their generous a n d efficient organization of the symposium. T h e responsibility for the selection and presentation of facts and for opinions expressed rests with the authors.

spécialisées, ont été présentés de manière à éveiller l’intérêt de collègues travaillant dans des domaines entièrement différents. Les discussions ont fait ressortir n o t a m m e n t la nécessité de créer des zones de contrôle protégées, de conclure des traités internationaux visant à protéger les oiseaux migrateurs, les baleines, les phoques, etc., et de mieux comprendre les fluctuations cycliques des mammifères et des oiseaux subarctiques, problème capital de l’écologie terrestre boréale. Les participants ont estimé qu’il faudrait, d’une part, effectuer des recherches sur la productivité et le rendement perm a n e n t de la faune et de lafloresubarctiqueset’d’autre part, multiplier et améliorer les observations météorologiques en vue de l’étude microclimatologique des zones subarctiques. Après la présentation des mémoires et la conclusion des débats, ont eu lieu une visite à l’université de Turku et u n e excursion de quatre jours en Laponie à destination de la station de recherche de Kevo. Les zoologistes, pour leur part, ont eu la possibilité de participer à une autre excursion jusqu’à la station biologique d’oulanka, qui dépend de l’université

d’Oulu. L’Unesco tient à exprimer sa reconnaissance a u x m e m b r e s d u colloque qui, grâce à leurs mémoires, lui ont permis de publier le présent volume, et à remercier le professeur Kallio et le comité d’organisation finlandais pour la générosité et l’efficacité avec lesquelles ils ont organisé le colloque. Les auteurs sont seuls responsahles du choix et de la présentation des faits, ainsi que des opinions exprimées.

Contents

J. Bliithgen

B. A. Tikhomirov

I. M. Dolgin

S. Huovila

H.Odin and K.Perttu

R. Sarvas

W.O. Pruitt Jr.

Table des matières

Problems of definition and geographical differentiation of the Subarctic with special regard to northern Europe . Problèmes de délfinition et de différenciationgéographique du S u barctique, spécialement en Europe septentrionale [Résumé] . Forest limits as the most important biogeographical boundary in the North . Importance des limites forestières en tant que frontière biogéographique dans le Nord [Résumé] . Subarctic meteorology . Météorologie subarctique [Résumé]

A. Corte

35 38 41

. de

63 65

Radiation measurements near the forest limit in northern S w e d e n . . Mesure du rayonnement aux limites de la forêt dans la Suède septentrionale [Résumé] . Temperature s u m as a restricting factor in the development of forest in the Subarctic . L a température globale en tant que facteur restrictif dans le développement des forêts subarctiques [Résumé] .

Quelques aspects écologiques

30

.4-59

.

S o m e features of the microclimate within hilly regions in Finland Quelques caractéristiques du microclimat dans les régions accidentées Finlande [Résumé] .

S o m e ecological aspects of s n o w

11

.

67

77

79 81 83

de la neige [Résumé]

97

't -

Bioecological aspects of the s n o w plant communities of C a p e Spring, Argentine Antarctica . .

101

Aspects bio-écologiques des communautés de plantes des neiges au cap Spring, Argentine antarctique [Résumé]

A. R a p p

.

S o m e geomorphological processes in cold climates Etude

.

de certains processus géomorphologiques dans les régions à climat

froid [Résumé]

.

.

104

.

105

.

113

J. Biidel

A. J a h n

Denudation and river erosion in the “zone of pronounced valley forma. . tion” o n South-east Spitsbergen Dénudation et érosion fluviale dans la zone de formation accusée de vallées au Spitzberg du Sud-Est [Résumé] . .

117

Soil m o v e m e n t s under the influence of freezing . mouvements du sol sous l’inyuence du gel [Résumé]

. .

119 122

Complexité des notions de faciès morphologique arctique et subarctique (nord-ouest et centre ouest du Groenland). Géographie boréale et anthro. pologie: fondements physiques des notions de lieu de territoire . Complexity of the terms LLArctic” and “Subarctic” as notions of morphological aspect (North-westand Middle-west Greenland) [ S u m m a r y ] .

125

Les

J. Malaurie

R. J. E. B r o w n

.

Permafrost as a n ecological factor in the Subarctic . écologique de la région subarctique [Résumé]

Le pergélisol,facteur

T.L. Péwé

M. Salmi

. .

.

Permafrost and vegetation o n flood-plainsof subarctic rivers (Alaska) : [a summary]. . Le pergélisol et la végétation dans les plaines inondables des cours d’eau . . subarctiques (Alaska) [Résumé]

115

128 129 138 141 141

Investigations o n palsas in Finnish Lapland . . Recherches sur les hydrolaccolithes (palses) de la Laponie Jinlandaise [Résumé] . .

151

143

E. Schenk

Permafrost and frost structures in the subarctic area Formation et structures du pergélisol [Résumé] .

. .

155 158

H.Svensson

Frozen-ground morphology of northeasternmost N o r w a y . . Morphologie des sols gelés dans l’extrême nord-est de la Norvège [RBsumé].

161

P. L. Johnson

R e m o t e sensing as a n ecological tool . L a détection à distance en écologie [Résumé]

J. C. F. T e d r o w

Soils of the subarctic regions Les sols des régions subarctiques [Résumé]

.

.

P7

. .

169 185

. .

189 199

F. di Castri R. Covarrubias E. Hajek

Soil ecosystems in subantarctic regions . Écosystèmes du sol dans les régions subantarctiques [Résumé]

. .

207 221

L. A. Viereck

Soil temperatures in river bottom stands in interior Alaska . . L a température du sol dans les peuplements forestiers du fond des vallées à l’intérieur de l’Alaska [Résumé] . .

223

. .

235 238

I. Hustich

On the study of the Sur l’étude

D. J. Bellamy W.M. Tickle

E. Einarsson

.

ecology of subarctic vegetation

de l’écologie de la végétation subarctique [Résumé]

.

232

A

critical limit of primary production for the survival of arctic alpine . . plants in the northern Pennines of England Un seuil critique de la production primaire pour la survie de plantes alpines arctiques dans les Pennines septentrionales (Angleterre) [Résumé].

241 246

Plant ecology and succession in s o m e nunataks in the Vatnajökull glacier

.

247

Phyto-écologie et évolution du tapis végétal dans certains nunataks du glacier de Vatnajökull, dans le sud-est de l’Islande [Résumé] . .

254

in South-east Iceland

.

.

A. N. F o r m o z o v

Ecologie des plus importantes espèces de la faune subarctique Ecology of the major species of subarctic fauna [ S u m m a r y ] .

A. G. Loughrey

T h e ecology and population dynamics of the barren-ground caribou in Canada Le caribou des toundras du Canada [Résumé] .

J. P. Kelsall

V. A. Peiponen

257 273 275 279

Animal activity patterns under subarctic s u m m e r conditions . Organisation de l’activité des animaux en fonction des caractéristiques de l’été subarctique [Résumé] .

281

Les îles Saint-Pierre et Miquelon, u n e enclave subarctique méridionale The St. Pierre and Miquelon Islands,an enclave of the southern Subarctic [Summary] .

289

. Forests a n d forestry in subarctic regions la sylviculture dans les régions subarctiques [Résumé]

.

295 300

R. Kalliola

. National parks a n d nature reserves in subarctic regions Parcs nationaux et réserves naturelles dans les régions subarctiques [Résumé]

303 307

I. G. S i m m o n s

Problems of the conservation of relict arctic a n d subarctic species in Britain Conservation des survivances botaniques arctiques et subarctiques en . Grande-Bretagne [Résumé]

317

Subarctic peatlands a n d their utilization Les tourbières subarctiques et leur utilisation [Résumé] .

319 325

E. Aubert

de la Riie

P. Mikola

Les forets et

R. Ruuhijärvi E. Ehlers

I

-. . *

-.

T h e rational use of forests and bogs, in view of comparative observations in north-western Canada and northern Finland . Utilisation rationnelle des forets et des marécages d’après des observations comparées effectuéesdans le nord-ouest du Canada et le nord de la Finlande [Résumé] .

286

292

309

327 333

E. Schenk

On the string formation in the aapa

moors a n d raised bogs of Finland . L’origine des tourbières réticulées (aapamoors) [Résumé] . .

335 340

G. Sirén

R e m a r k s o n current silvicultural research in the Subarctic of Finland . Remarques sur les recherches effectuéesen sylviculture dans la région subarctique de Finlande [Résumé] .

343 348

International scientific co-operation in conservation with special reference to peatlands .

349

/ Discussion générale et conclusions

351

T.Pritchard

General discussion and conclusions List of participants

/ Liste des participants

.

363

Problems of definition and geographical differentiation of the Subarctic with special regard to northern Europe Joachim Blüthgen

I should like to express m y appreciation for being invited to read the introductory paper which will set the scene and provide the frame for the w o r k of this s y m p o s i u m on the Subarctic. I a m aware that I can deal with only s o m e of the problems attached to this very complex and variably used term. T h e m o r e I worked o n the subject, the m o r e I doubted whether it is possible at present to give a satisfactory definition of this primarily geographical term which is also used in numerous neighbouring sciences though each gives it a different meaning. Although m y task is to try to define and subdivide the Subarctic I must confess that this-due to contributions which are still contradictory-is not quite objectively possible as yet. It reflects inevitably a great deal of personal opinion. I ask therefore that m y c o m m e n t s be regarded as a still incomplete contribution. It is b o u n d to be of a preliminary character since only m u c h m o r e painstaking investigations into the countless contributions to this subject could lead, in the near future, to a solution of this terminological problem. Besides, m o r e extensive contacts with competent specialists over the world are a primary necessity. T h e entanglement of terms is far m o r e complex than I originally assumed. Therefore I should especially like to acknowledge gratefully the proposal m a d e by Unesco to open the s y m p o s i u m with this topic. It really corresponds to a n urgently felt need to avoid as m u c h as possible all misunderstandings of w h a t is m e a n t by the term “Subarctic”. Thereby help is offered to all those specialists doing research on special problems which are in a n y w a y connected with the Subarctic, so that they might eventually be able to refer the results they have obtained to the right or at least a conventionally agreed u p o n frame. It will be the specific task of the geographer to form building-blocks from all the numerous individual results and interpretations, building-blocks to erect

the terminological structure for “the Subarctic”, to combine t h e m and to integrate t h e m into this structure according to their due weight. T h e geographical term “subarctic” is one of those geographical designations of areas which are often used for the characterization of transitional zones between core areas. Delimiting t h e m , however, is only possible in a complex fashion,i.e., by a combination of different distinctive features. T h e y are defined in different ways, if ever. W i t h subarctic w e can group subpolar, subtropical, suboceanic, subcontinental, subalpine. These “sub” areas form every one of t h e m a transitional zone at the periphery of those core areas which are formed by differentiation of the Earth according to latitude, surface, and height, and of whose n a m e s they are derived (arctic, tropics, etc.). B u t it is not possible to deduce clearly from their n a m e s whether they form parts of these areas or whether they are areas of their o w n outside them. These terms, which derive their n a m e s from geographical situations, are n o w liable to b e connected with the contents of various systems : plant-geographical, climatogeographical, pedological, ecological, etc., or they m a y b e used as terms in landscape or in the geography of population, h u m a n settlement, or econo m y . Their delimitation is not only different in the various branches of learning, but even within one a n d the s a m e field there exist serious discrepancies between different authors, according to which characteristic is stressed. W h e n w e look into geographical literature w e see at once the numerous different uses of these terms. T h e s a m e holds true in those m a n y neighbouring sciences o n which geography is b o u n d to rely. In the following pages I shall try to throw s o m e light o n the term subarctic a n d its use until n o w in various fields of learning a n d according to the geographical differentiation of its area, especially in

11

J. Blüthgen

northern Fennoscandia. Here w e can rely u p o n the w o r k done locally by the T r o m s ö M u s e u m in northern Norway, by the Abisko Research Station of the Royal Swedish A c a d e m y of Sciences a n d by the K e v o Subarctic Research Station of the T u r k u University near Utsjoki in northern Finland. These stations are likely to promote scientific research especially in the fields of natural sciences, ecology and geography. Of course I can select only s o m e instances taken from a rather broad range of this term’s uses. If w e first take a look into a differentiation of c o m plex landscape entities, w e choose the nine different subordinate types, into which Hassinger (1933) differentiated his m a i n type subpolare Landschaftstypen (subpolar types of landscapes) : 1. Lowland tundras (Kolas, Kanin, North Siberian a n d North Laurentian Lowland, North American arctic archip elago). 2. Highland tundras (Lapland, Finnmark, Desert Ural, eastern Siberian mountains, Chukchee Peninsula, Labrador Uplands, northern Kamchatka). 3.Alpine m e a d o w s (above the timber line in the mountains). 4.Cold high mountain steppes (Pamir, South a n d East Tibet, Tien Shan, P u n a of the Andes). 5. Cold high mountain deserts (western a n d northern Tibet). 6. Subpolar m e a d o w Islands (south-western Greenland, Iceland, Faeroe Islands, North-east N e w foundland, Aleutian Islands, Tierra del Fuego, Falkland Islands). 7. Subpolar forested plains (northern Sweden, northern Finland, northern Russian lowland, the taiga of western Siberia, Canadian coniferous belt). 8. Subpolar oceanic mountainous forest regions (northern Scandinavian mountains, North American Sea Alps, Newfoundland mountain area, A n d e s of Southern Chile and Tierra del Fuego, South K a m chatka, Sakhalin, Kuril Islands). 9. Subpolar continental mountainous forest regions (forested Ural, middle and eastern Siberian m o u n tains, Canadian Coast Range). This shows the term subpolar to be used in a very wide sense, as the continental forest regions of northern Eurasia including the western Siberian and Canadian taiga, the alpine m e a d o w s above the timber line in the mountains, the cold high mountain deserts of the Pamir, southern and eastern Tibet, and even the P u n a of the A n d e s are classiûed as subpolar, although being situated in very low latitudes. T o d a y this view is n o longer accepted, neither by geobotanists nor by most climatologists although this equalization of landscapes, which s h o w similarities only in thermal averages, in the related arcto-alpine flora, a n d in convergently similar growth forms (creeping a n d cushion growth), has been used for decades by other authors as well. T h e researches of Troll (1941, 1959) on m a n y tropical and ectropical mountains of the

12

Earth have s h o w n that mountain climates, despite certain similarities of rough averages with those of higher latitudes, are first a n d foremost the mountainous variations of neighbouring lowland climates. T h a t holds trile especially for the m a r c h of radiation a n d its consequence, the m a r c h of temperature. T h e relation between daily a n d yearly m a r c h of temperature is in both regions, i.e., the tropical high mountains and the polar lowlands, basically different. In the European area w e have in addition the historical factor that the arctic floristic element has receded after the post-glacial increase in temperature from the up till then subarctic-periglacial middle European lowland partly into the Alpine height zones, partly into those areas of northern Europe adjacent to the pole. This floristic relationship, forced as it w a s by the immigrational history of the plants, has contributed to the error of equalizing the accompanying climates. Besides, this has been favoured by the fact that, from the Alps to the Barents Sea, the arctoalpine element of the flora is found towards the north in successively lower mountain regions, until it is last m e t with near sea level along the coast of the Barents Sea. W i t h this last point in view w e approach a problem which produces difficulties in delimiting the Subarctic not only in Fennoscandia but everywhere. It holds true for all regions where meridionally arranged mountain ranges of middle to higher latitudes cause the alpine height zone to pass into the subarctic lowland region. That is not only the case in the Scandes but also in the Urals, in s o m e north-east Siberian mountain ranges, on K a m c h a t k a a n d in the North American R o c k y Mountains. In all these regions coldadapted plants m o v e d either to a greater altitude or to the north w h e n the climate b e c a m e milder after the disappearance of ice. T h e time elapsed since then is too short a n d the difference really existing between high alpine a n d subarctic climate is not of such vital importance for these plant associations to cause adaptation by differentiation within the plant life. Besides it is generally k n o w n that there are s o m e circumpolar plant areas which have not taken part in this retreat into greater altitudes, but which have followed the receding ice towards the north. T h e wellk n o w n Atlas of the distribution of vascular plants in N. W. Europe by Hulten (1950) shows instructive examples. Despite the floristic relationship, and s o m e ecological similarities, it is nevertheless important to keep in mind that there are differences between the arctic a n d alpine elements of the flora d u e to the migrational history. In animal geography such differences are perhaps even m o r e striking if w e think of the circumpolar occurrence of the reindeer, the lemming, and other species which d o not exist in the middle European alpine area a n d the transplantation of which has not

Problems of definition and geographical differentiation of the Subarctic

been possible. In the post-glacial time they followed the receding ice to the north exclusively. Let us take a look into the differentiation of the

the “Subalpine Birch W o o d ” as further independent zones. It is clear that he regards the extension of his subarctic proper as very narrow and excludes the

Earth according to landscape belts which Passarge published in 1923. For along time his system played an important part at least within middle European geography. Within the polar areas Passarge distinguishes the Kültewüsten (cold deserts) and the Kültesteppen (cold steppes). The latter only are of interest to us. He divides t h e m into the Tundralünder (tundra areas) and the Subpolare Wiesenlünder (subpolar m e a d o w areas). When dealing with the tundra he mentions its different aspects : Kümmertundra (poor tundra), Torfhügeltundra (peat-hill tundra), Flechtenrundhöcker (lichen covered roches moutonnées), and Waldtundra (forest tundra), but he does not use them for a systematic sub-division. The t e r m subpolar does not appear in this last group, but only with regard to the subpolar m e a d o w areas and outside the polar areas in the sub-division of the so-called “middle belt”. Here are distinguished a m o n g others the “subpolar inland coniferous areas’’, i.e., the taiga, as a separate type within the middle belt, notwithstanding its extension very far south in Canada and Siberia. The “forest tundra” is mentioned as the main living area of the reindeer and is s h o w n on the outline m a p as a narrow strip parallel to the polar border. All these areas, which are first treated as natural landscapes, s h o w a specific form of utilization by m a n also dealt with by Passarge. In plant-geography proper, the term subarctic or subpolar zone is found relatively early. However, it covers not so m u c h ecological zones but mostly areas based o n floristic elements, e.g., Engler’s area of subarctic flora that he places between his tundra zone-which he, by the way, n a m e s “arctic”-and his deciduous forests of the middle latitude (Engler and Drude, 1896-1928). In designating the Boreal Coniferous Belt or the taiga as subpolar, he has been followed by m a n y geobotanists and climatologists as far as they constructed their climate systems according to climatic effects o n vegetation. Hettner (1935) joined this group. Lundegårdh (1957) also identified the southern limit of the polar zone with the northern limit of the forest zone and classiíied the taiga as subpolar coniferous zone without further sub-division. A m o n g plant geographers w h o use the term subarctic, its geographical delimitation is variable. Let us take a few examples only. Walter (1954, p. 151) identifies the area of the subarctic flora with the forest tundra and regards it as a sub-division of the arctic geo-element. Sjörs (1965, p. 50), on the other hand, ascribes a plant-geographically independent character to the subarctic outside the Arctic proper, but his subarctic covers only the northern taiga, to which he adds towards the pole the “Continental W o o d l a n d Tundra”, the “Alpine North Ural”, a n d

Birch W o o d as well as the W o o d l a n d tundra a n d even the real tundra. We can see the huge discrepancy which exists, as regards the conception of the subpolar area, between Engler and Sjörs. In his earlier w o r k (1956) Sjörs criticizes the equalization of “high boreal” and “subarctic”. In accordance with the animal geographer E k m a n he preferred to n a m e the northern taiga regions “high boreal” and equalize the Subarctic only with Grigoriev’s (1956) forest tundra and the “hemiarktis” of Rousseau (1952). But, as w e have seen, Sjörs has altered his definition of subarctic in his new book of 1965. After numerous earlier investigations concerning the question of vegetational zones in Labrador, Rousseau (1964) published an important classifying contribution which differentiated the problem, at least for East Canada (Labrador), to a higher degree. In a biogeographical description, which partly follows up the researches of Hustich (1939) in Labrador, he distinguishes, between his temperate and arctic zones, the Subarctic and, adjacent to it to the north, the hemiarctic zones as transitional zones, both belonging neither to the arctic nor to the temperate,i.e., boreal, zones. The temperate zone is extended to that line where profitable mixed coniferous forests of Picea glauca, Picea mariana, Abies balsamea, Populus tremuloides, Betula papyrifera, partly also of Thuja occidentalis cease to form dense stands. This is the timber line of forest economy. In the subarctic zone coniferous forest of the taiga type is predominant o n dry and wet sites, very often interrupted, however, by bogs a n d generally open and sparse compared to the boreal zone. It is the “parc subarctique”. Real tundra is not found in this area, but w e find scattered permafrost cores already. The tundra is only partly found in the hemiarctic zone where it is associated with sparse forest stands and tufts of Picea mariana and Larix laricina, on h u m i d sites with S p h a g n u m mosses and o n drier sites with Cladonia lichens. This zone is physiognomically and ecologically the equivalent to the Eurasian forest tundra. L o w tree growth is concentrated to the water edge, to s o m e tufts in h u m i d hollows or to sheltered valley stretches. On the exposed treeless areas the flora of the tundra or the north Scandinavian m o u n tain heath, as the case m a y be, is dominant, which are intimately related to the alpine flora. In the arctic zone proper, in conclusion, as far as it can be a habitat for plants at all, w e find humidity- or dryness-adapted tundra, characterized by small Betula glandulosa trees, dwarf bushes ( E m p e t r u m hermaphroditum), Cladonia, Carex, and S p h a g n u m species. For our problem it is of importance that the tundra proper thus is regarded by Rousseau as part of the Arctic, and not as belonging to the Subarctic or hemiarctic.

13

J. Blüthgen

On the other hand it is of principal importance that Rousseau regards the northern transitional belt of the taiga as subarctic. This discriminating description of the plant-geographical transition belts between the arctic vegetation of northern Labrador and the boreal main region is also accepted by Knapp (1965) in his recently published book on the vegetation of northern and middle America. H e already calls subarctic the dissolving open border area of the taiga, which is interrupted by bogs and habitats of arctic elements of flora. This is the “Open Coniferous Forest” of Ritchie (1960)and the “Open BorealWoodland” of Hare (1950), in which w e again find indistinct names and where boreal and subarctic are used as synonyms. Finally w e have, in connexion with the mountain birch forest of northern Europe, the term “subalpine zone” which,since Wahlenberg’swork, Flora lapponica (1812), has been an integral part of plant geography in the north. Hustich (1960,p. 55) rightly protested against the continued use of this term, at least as far as the birch forests of Lapland are concerned, in his contribution to the volume, A Geography of Norden, which was prepared for the International Geographical Congress,1960,at Stockholm. In accordance with Grigoriev, to w h o m I shall return in a moment, his opinion is that the Subarctic ought to be a transitional zone of its o w n between the Arctic and the boreal coniferous zone. The question which Hustich has left out is just which parts of the hitherto Arctic and which parts of the hitherto boreal zone are supposed to form this zone. It looks as if in recent plant-geographical publications the view which has gained more and more ground is to regard the Subarctic as a basically independent belt. This is reflected in the representation of the sub-arctic zone by Schmithüsen (1961), which is widely used in Germany. H e shows the Subarctic to begin with the “northern tree and wood limit and the wooded tundra”. This is followed by further sub-divisionsof the Subarctic, viz., the “tundra belt” and the “belt of subarctic meadows” (Aleutians,Iceland), existing in those parts influenced by the ocean. They are also called “subpolar meadows” though the absence of birch trees in most of these oceanic places is not due to natural causes but to h u m a n influence. As an explanation it has to be added that the “northern wood and tree limit”is thought of not as a line but as a transitionalbelt. Ifw e compare this system with that of Rousseau mentioned above w e see that Schmithüsen,in opposition to Rousseau, regards the tundra proper as part of the Subarctic and not yet of the Arctic. W e shall return to this remarkable point later after having discussed the suggestions of Grigoriev. It is as difficult to define the Subarctic according to climatic criteria as it is according to plant-geographical-ecological criteria. W e shall first examine

14

h o w far a genetic point of view-which differentiates the climates according to the general circulation of air on the earth-is able to supply a basis for the term subarctic. A m o n g the older representatives of this school Hettner (1930) must also be named here. His genetic differentiation of climates gives no quantitative specihations of climatic measurements,i.e., no threshold values nor values of continuancy.Only when limiting the Subarctic (p. 96) he remarks that less than four months show a temperature of more than loo C. According to this statement a great part of the taiga ought to be assigned to this belt. In another of his works, however, (Hettner, 1935, p. 139) he identifies the subarctic zone as the outer belt of the Arctic proper and indicates a July temperature of 60 C to 100 C. A t about the same time Philippson (1933,p. 308) equalized the border between arctic and subarctic with the July isotherm of 50 C. If one examines these different statements for the special case of Fennoscandia, the differentiation made by Hettner is not at all satisfactory, because here he has three meridional belts of climate: the oceanic climate of the North Atlantic to the Scandes and the Varanger Peninsula, the polar climate within the Scandes from southern Norway to the Kola Peninsula, and the cold inland climate from the Bothnian area over the greater part of Finland to northern and eastern Russia. H e attempts no sub-division of his polar climate. Such contradicting statements can be of no help for our problem. A m o n g the younger climatogeographers we shall single out Alissow (1954).His system is based on the distribution of the belts within the general circulation, and on the extension of air masses during the single seasons. H e distinguishes between the arctic and the temperate zones a special sub-arctic zone limited by the position of the arctic frontal zone, i.e., that region where the west-east tracks of the cyclones of the ectropical west drift are nearest to the pole. The arctic frontal zone tends to be situated more to the north in summer than in winter. Where this occurs the result is a transitional zone with arctic air masses in winter and those of the temperate zone in summer. T w o special cases have to p e distinguished: (a) a continental zone with large temperature amplitude between summer and winter (North-east Yakutia), and (b) an oceanic zone with amplitudes of the highest monthly averages reaching 200 C (South Greenland and Alaska). A look into the corresponding m a p in Alissow’s book shows, on the other hand, that the “Subarctic” defined in this w a y is in part substantially different from the “Subarctic” based on plantgeographical and ecological investigations. According to Allisow, Iceland, as well as the whole area from northern Scandinavia to the estuary of the Yenisey is not a part of the Subarctic because in this region, according to Alissow, no seasonal shifting of the arctic frontal zone takes place.

Problems of definition and geographical differentiation of the Subarctic

A “Subarctic” climatically defined in this way, even though genetic, cannot be considered as satisfactory although it makes use of a complex climate constituent, the air masses. For, even if one might be inclined to concede that the subarctic character of northern Lapland is not very marked, this is not at all the case with the tundras of north-easternEurope. The arctic frontal zone or the winter invasion of arctic air alone cannot be deemed satisfactory as a climatic motivation. Besides, northern Eurasia is invaded by arctic air during summer with northern winds and during winter mainly by continental air with south to west winds (boreal zone of Flohn, 1950). A m o n g the numerous effective climate systems, which are based on the effects of climate on soil and vegetation,there is also no unanimity as to the separation of a Subarctic. First w e shall deal with Köppen’s classificationwhich is still widely used. His first classification (Köppen, 1900) was based exclusively on heat and humidity claims of plant life (he used the plant groups of D e Candolle). The term “subarctic” or “subpolar climate” does not appear at all. A m o n g the differentiated areas that of the birch climate of the plant group of microtherms (D)is of importance for northern Europe. During about four months only the temperature is above 100 C, reaching an upper limit of 190 C, while that of the coldest month lies somewhere between 30 C and -520 C, the annual amplitude of the monthly averages must at least be 100 C. Beyond the July isotherm of 100 C begins the realm (E)of the hekistotherms (E)or cold climates with the warmest monthly average between O0 C and 100 C. This is the polar-fox or arctic-tundra climate with a continental,large,annual amplitude of monthly averages between 200 C and 600 C,with a cold, long, and dry winter and a short but stable summer. In the next classification by Köppen (1918) the criteria for the belts under consideration here have been changed as well as their names. T h e coldest month of both areas (Dand E) is n o w below -20 C, the warmest of the snow forest climate (D)is above 100 C, the snow-rich tundra climate (E)is between O0 C and 100 C. Besides there is an explicit differentiation between ET (tundra climate) and EH (climate of altitudes above 3,000 m), which Köppen unfortunately abandoned again later. In his manual (1923) and later, in the wall m a p of the climates of the earth edited by Köppen and Geiger (first published in 1928, latest revision by Geiger in 1961) the D-limitof the snow forest climates against the temperate C-climates has been lowered from -20 C to -30 C of the coldest month; the border against the E-climates, which is of importance for Lapland, has stayed, however, as it was (warmest month 100 C = tree limit).In Lapland we find therefore the birch climate (Dfc) near to the tundra climate (ET).W h a t is important is that the areas in northern Europe appear to be rather arbitrarily limited and show no conformity with biological

border lines in this region. A subarctic climate of its o w n is never mentioned. This Köppen classification&hasbeen modified-several times, and that which Trewartha (1954) undertook became widely known in the last decade.As the coldest subtype of his “humid microthermal climates” (D) Trewnrtha united the types Dcf, Ddf, and D c w to a “subarctic climate”. It forms a large belt which extends into the mountains of Central Asia and which comprises the greater part of the taiga. Stretching from the latitude of Oslo-Stockholm-Helsinkiright to the Barents Sea in northern Europe,it is interrupted only by the “tundra climate” (ET)of the Scandes. As with Köppen this is assigned to the polar climates (E).In this w a y another untenable definition of the Subarctic has been given, for neither is the climate of Helsinki subarctic, nor is the climate of southern Norway arctic, quite apart from the disputable identification of the tundra climate with the arctic climate. At least the Subarctic is not regarded as belonging to the Arctic, but its extension to the border of the boreal forests against the steppes in rather low latitudes need not be discussed. In a similar w a y Blair (1954)defined his subpolar climate, which he regards as a main type of its own, but which he equalizes with the whole taiga as well. In this last respect it really was a progress when von Wissmann (1966) did not extend his “subpolar climate” into the forest zone but equalized it with the climate of the tundra. With this however, the subpolar climate is limited to a rather small fringe along the coasts of the polar seas. As the 100 C isotherm of July is taken by him as the limiting value, the birch forest and the forest tundra, as well as the oceanic “meadows” of Iceland remain outside the subpolar zone of von Wissmann. In the m a p of climates which was published at the same time and in the same book by Creutzburg and Habbe (1966) the term “subpolar climate” is used in a separate way, limited by the isochiones (lines of the same length of snow cover) of 150 and 240 days respectively which means, in terms of temperature, between the July isotherms of 70 C and 110 C in oceanic regions. Taking into consideration the wetter and drier variants the subpolar climate of northern Europe extends towards the equator to the south Norwegian mountains and still includes the Bothnian Gulf and Lake Ladoga. The southernmost point of the subpolar climate on the whole of the Earth is in this presentation the northern point of Hokkaido and the mountain area between Lake Baikal and the sources of the Amur. W h a t was said above about Trewartha’s subarctic climate applies to the subpolar region of Creutzburg and Habbe as well: though it forms a belt of its own, outside the Arctic, it reaches m u c h too far into middle latitudes. T o conclude this climatogeographical comparison w e shall examine the m a p of the seasonal climates of

‘15

J. Bliithgen

the Earth by Troll and Paffen (1965),which is mainly based on the ecological needs of vegetation and which is the most differentiated of all climate classifications. Within Zone I (polar and subpolar zones) it shows the “subarctic tundra climate” and the “subpolar, high oceanic climate”. The first is found, as the n a m e implies, only on the northern hemisphere and there it comprises mainly the tundras north of the polar wood and tree limit.The warmest month of this zone averages 60 C to 100 C,the coldest stays below -80 C. In the Hudson B a y area, as was to be expected, it advances farthest south including the north-western shore of James Bay. In Eurasia it extends,in a margin parallel to the coast, from the neck of Kamchatka to northern Russia and from there to the west slowly narrowing to the north coast of Kola, Varanger Peninsula, and Mageröy, and thereby assigns the greater part of Lapland to the continental boreal climate of the following “cold temperateboreal zone”. T h e oceanic variety, which w e m a y conveniently call “subpolar high oceanic climate” has cool summers (warmest month 50 C to 120 C), only moderately cold winters (coldest month 20 C to -80 C), a relatively small amplitude, and lower temperatures not frequently below 100 C. It is represented in the subantarctic islands, in the southern half of Iceland and in the Aleutians. Vegetational areas are taken as the starting-point for this differentiation of climate for which thermic threshold values, etc., are then found. T h e main problem, i.e., the extension of the Subarctic,is again brought back to the plant-geographical-ecological question of which formation is still “subarctic” and which is already “cold temperate boreal”. T h e area of the Scandinavian mountain birch forest is accordingly, in northern Europe, placed mainly within the oceanic and continental boreal climate, in Iceland within the subpolar high oceanic climate, and in northern Iceland and south-western Greenland within the arctic tundra climate. This statement must not be taken,however, as the proof of a wrong climatic differentiation but is in accordance with the fact, stressed by the present writer in his geographical investigation into the Scandinavian mountain birch forest (Blüthgen, 1960) as a landscape formation, that the birch forest comprises an extensive climatic spectrum and, as a vegetational formation, is therefore not appropriate for a climatological-ecological definition and delimitation of the Subarctic. Only incidentally and for the sake of completeness should it be mentioned that on the ocean a marine subarctic zone can also be differentiated and its delimitation is even m u c h less problematical than the terrestrial one. T h e unanimous opinion of all oceanographers is that those ocean areas are subarctic,where “subpolar convergences”, i.e., mixing zones between cold arctic and warmer water, occur and which show in some cases an oscillating movement in their annual

16

march. At the same time these are the areas where polar drift ice seasonally appears. These are the “polar fronts” of the seas. F r o m year to year these areas show as large and irregular oscillations of situation as their atmosphericalcounterparts. In view of this it is understandable that there is some uncertainty as regards their delimitation in certain areas-for instance in Baffin Bay, as shown by a comparison of the limits of Schott (1942) and Dietrich (1964)-but the criteria as such are fortunately not disputed. T h e subarctic ocean areas are relevant for the problem of delimiting the Subarctic on the continents for yet another reason. In all those cases where the Subarctic on the continents extends very far south of the polar circle, with tundra, forest tundra, birchwood or “subpolar meadows” in its lowland variety, it is neighbouring subpolar ocean areas which are responsiblefor it :Iceland,southern Greenland, Labrador, the northern part of Newfoundland, Kamchatka. T h e sub-arctic ocean areas are therefore a great help to delimit the terrestrial Subarctic as well, where this extends south of the polar circle. By far the most important,ecologically far-reaching and thoroughly substantiated presentation of the Subarctic has been given by the Russian physiogeographer Grigoriev (1956). This well-known author carried out his first field work on this topic in the area of the Bolshezemelskaya Tundra in north-eastern Russia. This dates back to 1904. T h e book containing not only his o w n but also numerous other detailed researches,mainly Russian, and appeared for the first time in 1946. In the second edition, also prepared by the author himself, special attention is given to radiation measurements and calculations published in the meantime by Budyko (1955) and to the ecological field work of Tikhomirov (1960). W e should take a closer look into this fundamental work which is as far as I k n o w the first comprehensive treatment of the term “subarctic” in literature form. I was able to use parts of a translation that has been started by the Verlag H.Haack, at Gotha, whose help I wish to acknowledge here. It is to be hoped that the full translation w ill soon be published, as this work is not widely known. It offers an ideal starting-pointfor a discussion of the ecological findings related to the Subarctic in general. T h e term subarctic as used by Grigoriev originates mainly from plant-geographical-ecologicalfacts and that means from climato-geographical, pedological and hydrological facts too. His book deals with the nature of the Subarctic; however, its importance for h u m a n settlement, economy, and transport is hardly touched upon. The Subarctic covers roughly the areas of the “subarctic and arctic tundras” of the geobotanists. It is of special importance that “subarctic” refers to an independent geographical zone extending between the arctic and the temperate zones, including the boreal zones. The decisive conditions

Problems of definition and geographical differentiationof the Subarctic

for this are: (a) low, but in summer still positive radiation balance, predominantly cold air masses in summer also; (b) cyclonic activity with frontal precipitation; (e) discrepancy between low radiation effect and high humidity surplus in air and soil during summer; (d) low summer temperatures with monthly averages below 100 C to 120 C and very low temperatures of the thawing soil; (e) excessive humidity of the soil in summer. Grigoriev divides his subarctic belt into two zones, the Russian designations of which, priarkticesky and priborealny, might be translated into English as “pararctic” and “paraboreal”. T h e paraboreal zone in its turn is divided into a northern subzone (of moss and lichen tundra) and a southern subzone (of bush and forest tundra). The pararctic zone is equal to the “arctic tundra” of m a n y plant geographers, as the paraboreal is to the “subarctic tundra”. Further on I shall use this division of the Subarctic in a “pararctic” and a “paraboreal” subzone which was also introduced and proposed by Grigoriev, but with some deviation from Grigoriev as regards the paraboreal subzone. For this zonal differentiation based on plant-geographical facts Grigoriev found climatological averages and extremes. The radiation balance which is positive only in the three or four summer months and only near the surface with temperatures above freezing-point has the effect that the frost, which has penetrated the soil more or less deeply during the other eight or nine winter months-there are no transitional months in the sense of spring and autumn in the middle latitudes-is not altogether annihilated. Permafrost exists but regionally differs as the type of soil, drainage, vegetation cover and exposition cause locally highly variable temperature balances. However, it must be said, here that the Subarctic is not identical with the area of the permafrost (Fig.1). In continental regions the permafrost is known to advance far into middle latitudes beyond the Subarctic;but it is altogether absent in some high oceanic regions of the Subarctic. In areas with permafrost the result is that the depth of thawing varies intensely during summer when water concentration is high and evaporation relatively low, because the air is-due to the low temperatures-mostly near saturation point anyway and has therefore practically no power of evaporation. This abundance of cold melting water in the thawing soil, especially in flat areas, is one of the main characteristics of the Subarctic and the decisive phenomenon of the tundra in its various aspects. American scientists, however, have identified the southern boundary of the discontinuous permafrost with the southern limit of the Subarctic itself (see Brown, 1969), but this is a doubtful definition because permafrost depends not only on the arctic radiation balance but also on the degree of continentality.

“Continentality” is a complex term which cannot be derived from arctic conditions alone. In addition to Grigoriev’s list the so-called subpolar meadows should be included in the paraboreal Subarctic. These are mainly free of permafrost and receive their high soil humidity during summer also from abundant precipitations at low air temperatures which forbid high evaporation. They belong potentially to the forest tundra in the form of low birch wood, their present treelessness being the result of man-made deforestation during past centuries. The cold thawing soil prevents the plants from absorbing greater amounts of water or nourishment, with the effect that dry periods or sporadic w a r m days-which even in the Subarctic m a y for a short time cause extremes up to 300 C (cf. Lembke, 1947) with the help of the summer midnight sun and appropriate weather conditions-may cause withering damages. Therefore the exposed plants, especially evergreens,are normally protected against such strain by the xerophytic structure of their organs, by cushion growth, and by being able to adjust the openings of their stomata, though this latter statement has not been verified by other writers. The root net is very often so superficial,that it is restricted to the not very thick layer of raw h u m u s on the mineral soil and is subjected to its extreme variations of humidity. A deeper penetration of the roots into the mineral soil is m u c h too risky for the plant because the fluctuations of temperature around freezing-point which are frequently met with in the Subarctic, even in summer, and the extreme variations of temperature cause breaking damages at the border line between raw humus and mineral soil. Accordingly only a very thin layer of air and soil, on or near the surface, offers enough heat to some subarctic plants, i.e., the “microthermals” of D e Candolle. The characteristic water concentration of the subarctic soil is caused above all by four factors 1. Thawing water in the soil above the permafrost layer. In case of missing permafrost,i.e., in oceanic climates,supersaturation of the soil by high and frequent precipitation compensates lacking melt-water to a certain degree during middle or late summer. 2.Melting water of the winter snow accumulated during eight or nine months outside oceanic regions. 3. L o w evaporation of altogether 10-12per cent only of the annual precipitation, lowest in oceanic and somewhat higher in continental parts of the Subarctic. 4.M a x i m u m precipitation in late summer outside the oceanic regions of the Subarctic, compensating evaporation losses during this period. It is true that global radiation during the summer is high due to the long polar days; in some parts it is even higher than in more southern latitudes. However,the low daily arc of the sun,the high percentage of diffuse light, the effective emission approaching

17 2

FIG.1. Distribution of sea-ice and permafrost (partly after Handbook of Geophysiology, 1960).

Land-ice within arctic and subarctic regions Continuous permafrost Discontinuous permafrost

14C

Sporadic permafrost

I\\y

Subarctic drift-ice High arctic pack-ice

120

100'

80'

O L " - "

500

1000

1500

2000krn L

J. Bliithgen

50 per cent (a consequence of the counter-radiation being reduced by l o w content of absolute water vapour and carbon dioxide), the screening against direct sun radiation during the s u m m e r by fog (mainly in sea a n d coast areas), the consumption of melting heat which continues far into the s u m m e r , a n d the high albedo as long as ice a n d s n o w are covering soil and water surfaces, all contribute to obtain only a small degree of w a r m i n g of the ,air. However, the climatic difference between the layer of air near the ground (or even within vegetation cushions) and the normal height of 2 m within the Stevenson screen (which is normal in climatic measurements) is not smaller than in l o w latitudes. On the contrary, the vertical lapse rate above the ground is often extremely high. In north-eastern Land, that m e a n s even within the high Arctic, D e g e took temperature measurements of 250 C to 280 C within vegetation cushions when the surrounding air at normal height showed only 40 C to 50 It is a specific characteristic of the Subarctic that due to its latitudinal situation the s u m m e r insolation surplus is still large enough to cause absence of s n o w after having subtracted the required melting and evaporation heat. T h e soils surface plays a n important role in the transformation of short-wave radiation energy into heat radiation, which is not so m u c h the case in the Arctic proper or at least not in a significant measure. On the other hand, the heat gain is so small that in this zone the heat s u m which is necessary for tree growth is either not obtained or, if it is, it only allows for a rather scarce a n d slow production of w o o d tissue. This is, as mentioned before, due to several factors. T h e small heating effect is mainly due to water temperatures which remain low in the polar seas and, because of melting ice a n d water turbulence rise only immaterially above freezing-point so that the air over the seas remains cold by conduction and exchange, a n d obstinate s u m m e r fogs are formed. T h e fact that air pressure over boreal continents is in s u m m e r generally s o m e w h a t lower than over the polar seas leads to the frequent inflow of cold, foggy, arctic air into the continental subarctic regions thus seriously and frequently lowering the air temperature. T h e subarctic flora is adapted to these continual temperature setbacks, as s h o w n by Tikhomirov in several studies about plant life in northern U.S.S.R.: it can d o with only low degrees of temperature in the surrounding air, its vegetation period already starts at a little above freezing-point a n d s o m e biological activities within the cells begin even at a time w h e n the air temperature is still s o m e w h a t below freezingpoint. W e k n o w besides, that not only within the cushions but also in cavities beneath the crusted s n o w the temperature m a y reach positive degrees. T h e adaptation of vegetation to a short w a r m period is s h o w n by a certain acceleration of growth due to long

c.

20

daylight and a corresponding reduction-but not abolition-of the daily time of rest and by prolonging biological phases over several summers. Forming of buds, development of leaves, flowering, seed maturation, seeding, a n d germinating are often spread over several years. This leads to the fact that plants of the Subarctic reach a n especially old age. T h e annual growth-rings of hibernating plants are therefore extremely narrow. K i h l m a n (1890) counted 544 growthrings o n a small juniper tree of 83 m m traverse in the Kola forest tundra. T h e formation of seed in the flowering plants is mostly effected by self-pollination helped by the ever-blowing wind as pollinating insects are often lacking. T h e observation of increased vegetative propagation of numerous species of the subarctic flora gives the s a m e result. In the forest tundra this p h e n o m e n o n is also found a m o n g ligneous plants such as birch a n d spruce. M a n y a multi-stemmed isolated spruce tuft can b e traced to the rooting of weighted-down branches of a n o longer existing central mother tree. W i t h the birch it is the power of developing n e w sprouts at the base of the trunk, which leads to polycormia after the trunk h a d either died or been felled (Fig.2). As to the animals’ adaptation to their subarctic environment a n d their w a y of survival w e shall mention the detailed investigations of F o r m o z o v which will soon be published in English (translation by the Boreal Institute, University of Alberta, E d m o n t o n , Canada). In this connexion w e m a y mention only the following facts. Animals that are very characteristic of the terrestrial Subarctic are the reindeer, the polar fox, the tundra wolf, the l e m m i n g a n d other rodents, a great variety of insects (especially gnats), numerous rapacious birds a n d several species of geese, ducks a n d swans, which populate the tundra in s u m m e r after having returned from their winter shelters. Those animals which stay in the Subarctic during winter m u s t be prepared to overcome the long, stormy winter with a densely packed s n o w cover. S o m e species can d o this either by storing fat reserves and reducing their activity during winter or by hibernating under the s n o w cover as the lemmings and other rodents do. S o m e retire to the taiga where weather conditions are m o r e favourable a n d s n o w is not so tightly packed. Along subarctic coasts the birds of prey are often concentrated o n suitable bird cliffs from where they start for their catch flights over the sea, in very m u c h the s a m e w a y as fishermen d o from their crowded villages. W h a t has been said about the plants’ struggle for life in the Subarctic also holds true, although in another manner, for the subarctic fauna. F o r m o z o v (1969)wrote: “ L e m o n d e animal subarctique est très original, pittoresque; ses représentants possèdent d’excellentes capacités d’adaptation a u x dures conditions d’existence”’ The southern limit of the Subarctic is to most authors identical to the forest limit which they think

1

Problems of definition and geographical differentiation of the subarctic

FIG. 2. Subarctic birch wood in northernmost Finland, near Karigasniemi, showing mountain birch (Betula tortuosa) with typical polycormia; in the foreground shrubs of dwarf birch (Betula nana) (Blüthgen, 1960).

of as showing the existence of m o r e or less open stands. T h e considerable disintegration of the taiga forest at its subarctic border reflects the variations of habitats around the absolute limit of existence valid for the whole Subarctic. B u t this delimitation, which already assigns the subregion of the forest tundra as paraboreal to the Subarctic, is at the root genetically unsatisfactory, though physiognomically striking. It is m u c h m o r e important to choose the limit of seed ripening of the forest trees as the southern limit, which is also called rational or reproductive, or generative forest limit. T h e distribution of ripe seeds by the wind over long distances is therefore the deciding additional factor which determines the actual forest limit. In this connexion the high effectiveness of the chionochore transport of last year’s seed, i.e., over a crusted, spring snow-cover, m u s t b e mentioned. A t the extreme periphery of ita ever happening, seed ripening occurs only at intervals of m a n y years. T h e distribution of ripe seeds into the Subarctic also, occurs only at intervals of m a n y years and from isolated favoured mother trees. If the limit of sufficient reproduction or seed ripening-let us say every fifth to tenth year-is taken as the basis for the southern delimitation of the Subarctic, a forest belt of trees still growing without hindrance but which are no longer capable of annual reproduction, belongs to the paraboreal sub-zone of the sub-Arctic. This is the southern belt of this subzone which, besides, is physiognomically interrupted and broken up by bogs a n d areas which are unfavourable to growth. In the northern part, the forest tundra, including the northern parts of the Scandinavian mountain birch forests, is prevalent. This limit of reproduction should coincide with the timber line, that is, the border of economical forest exploitation.

As w e have seen, the existence of permafrost cannot be identified with the Subarctic because this phenom e n o n , in its southern-most occurrence reaches well into the steppes of Transbaikalia. Permafrost is accordingly only one of m a n y factors. H o w e v e r ihere are subarctic areas free of forests which d o not s h o w the development of continuous permafrost. This occurs in the oceanic regions of the Subarctic-as already stated-where winter temperatures are not l o w enough but s n o w cover offers satisfactory protection so that frost cannot penetrate to any depth worth mentioning. In these oceanic regions of the Subarctic the too low s u m m e r temperature is the forestpreventing factor. This applies mainly to Lapland, but perhaps also to a certain degree to Iceland a n d the Aleutians a n d this special problem is still far from being solved. T h e question whether Lapland already belongs to the Subarctic is not easily answered. Here w e encounter the plant-geographical peculiarity of the mountain birch forest, extending as a peripheral belt, at the forest limit from the high mountains and viddas of southern N o r w a y to the Barents Sea. It consists of the birch species Betula tortuosa (see Fig. 2), which in its habitus is different from the other birches, but which is regarded by s o m e botanists only as a subspecies of Betula pubeseens. There are hybrids, in fact, but hardly ever at the periphery of its occurrence. It is easiest to judge the difference of habitus if one happens to c o m e across t w o “pure-bred” specimens near to each other o n the s a m e spot. Its wide-spreading growth and the missing tendency of having branches hanging d o w n is a sure sign of the difference between the mountain birch and the other species. It is able to stand wet, cool s u m m e r s and therefore spreads m o r e easily in this climate than pine or spruce. During the 21

J. Bliithgen

FIG.3. Young pine trees (Pinus silvestris) above the birch region on the top of Kaunispää (540 m), Raututunturit (northern Finland) (Blüthgen, 1960).

climatic amelioration of the last decades, especially

in the 1930s, a striking advance of the coniferous trees has been observed, even overtaking the birch zone. This amelioration shows itself at all seasons and not only in the spring, as s h o w n b y the temperature curves for Karesuando for different time periods (see Blüthgen, 1966, p. 575). Perhaps this long-range thermal variability might be regarded as typical of the S u b arctic. The result was that pine seedlings appeared spontaneously in a wide area, not only within the birch region but even beyond in the regio alpina or pararctic subzone, a fact on which Hustich has also c o m m e n t e d several times. One of the reasons for this p h e n o m e n o n w a s that better germinating conditions were m e t with outside the birch zone than within the almost luxurious, herbaceous, ground vegetation of the birch woods. It is remarkable and material for the critical estimation of these findings that nowhere at that time could older witnesses of such a far advance, neither living nor dead, be found. A visit to such places, where the pine had appeared and taken root in the 1930s, when repeated after fifteen years, showed this clear picture to be muddled up somewhat. It is true that, for instance on Kaunispää in Finnish Lapland (540 m above sea-level) in 1960, numerous pine trees at least 1-2 m high were found (Fig. 3), where in 1939 only young plants had grown under winter s n o w cover.Theselittle trees had obviously endured the process of growing u p from under the protecting winter s n o w cover. The s u m m i t of Kaunispää (in the Raututunturit Mountains) is wind-exposed and does not provide the protection of a thick layer of snow. The especially critical late-winter period with icy arctic north-eastern winds from the polar sea, s n o w being blown over a s n o w crust, low absolute humidity, and already effective sun radiation, has

22

done no d a m a g e to these young pines. However, the young pine and spruce trees, which were found in 1936 on the isolated s u m m i t of Dundret (823 m), near Gällivare in the alpine region above tree limit, were in 1952 partly withered or at least d a m a g e d at the height of the winter s n o w cover. But this isolated summit is n o longer situated in the subarctic ; besides, the withering damages might have been a negative effect of the warming of the last decades (Blüthgen, 1952). The birch (Betula tortuosa), o n a visit in 1952 in the fell areas south of Lake Torneträsk, showed a under large n u m b e r of hand-high seedlings-still s n o w protection during winter-obviously flown there, into open stands nearly man-high (near Yassijaure) and which filled the gaps in the old stands that evidently h a d been thinned by m a n a long time ago. The definition and differentiation of the Subarctic which Grigoriev prepared for North-east Russia cannot entirely be applied to northern European, i.e., Fennoscandian, conditions despite the relative vicinity of these areas. A b o v e all the Scandinavian mountain birch forest in its uniformity against neighbouring formations is a disturbing factor. It is geographically an extremely characteristic landscape p h e n o m e n o n of Scandinavia from the south-westernviddas of southern N o r w a y to roughly the area around and east of M u r m a n s k on the Kola Peninsula. Therefore, as a geographer, one might not be inclined to divide it for the sake of giving a definition of the Subarctic. Physiognomically, it is so clearly a distinct vegetational region of its o w n , in vertical as well as in horizontal extension, that it is a very important geographical characteristic of Fennoscandia which has no counterpart anywhere in the world. E v e n on Kamchatka, which of all the regions of the world might be taken

Problems of definition and geographical differentiation of the Subarctic

into consideration, things have s o m e w h a t different aspects in so far as a broad birch region with Betula ermanii does indeed exist there but not as the uppermost forest belt, for the tree a n d forest limit itself o n K a m c h a t k a is formed by a narrow area of dwarf pines (Pinuspumila) a n d others which are not found in Scandinavia. A closer view of the regio betulina of northern Europe, which w a s studied thoroughly for the first time in 1913 by Fries shows, however, regional differences which allow a differentiation and partition of this area with regard to a delimitation of the S u b arctic. In the above-mentioned contribution to the Stockholm International Geographical Congress in 1960, the author divided the birch forest into several geographical facies. T h e term “facies”, originally derived from geology, has been used in this connexion in a n e w sense for the investigation into geographical landscapes, different also from that peculiar sense m a d e widely k n o w n by the plant sociology of BraunBlanquet. In the above-mentioned contribution t w o large areas, the southern and the northern, were named. T h e northern which begins at the Jämtland mountain pass and the sub-division of which is alone interesting to us, shows seven facies belts, viz., the polar-maritime margin facies, the northern Atlantic fjord facies, the northern subcontinental valley and plateau facies, the northern continental margin facies, the subarctic valley a n d plateau facies, the subarctic margin facies, and the Barents Sea facies. Only the first and the last three mentioned are to be regarded as and combined to the subarctic confacies of the birch forest. A s subarctic characteristics c o m m o n to all these there are s o m e climatically affected traits such as ; the occurrence of cold, late-winter, polar-sea winds over a s n o w cover remaining well into M a y , large daily temperature oscillations immediately above

the s n o w cover due to the rapidly increasing length of day, and increased evaporation power of arctic air poor in water vapour. A s a result of these conditions, only imperfectly reflected in the values recorded by the scattered climatic stations of this area, vegetation, in order to survive, greatly needs the protection of the snow. Therefore shearing damages begin to appear at the height of the early spring s n o w cover (table birches (Fig. 4) a n d analogous forms with other bushes) ; but a superficial journey through northern Lapland (in 1960, along the road from Ivalo via Karigasniemi-Karasjok to the Porsanger Fjord) showed against all expectations surprisingly f e w shearing damages within the regio betulina. T h a t m a y , however, be caused by the road having been built as m u c h as possible across protected areas. A visit in 1966 has s h o w n that such p h e n o m e n a are only scarcely found in the regio betulina of Utsjoki. Nevertheless H ä m e t Ahti (1963)in her detailed plant-sociological analysis of the mountain birch forest of northern Lapland mentioned t h e m as one of the characteristics of her “oceanic subalpine birch forests”, (for instance o n the Varanger Pensinsula and at Utsjoki), while they are not mentioned for the submaritime nor for continental-subalpine subzones. N e a r to the polar sea the exposure to the sun (“sydberg-vegetation”), which at the s a m e time m e a n s protection against the cold polar sea winds, plays a major part in the distribution of higher vegetation, this being a striking feature of the Subarctic. Within the small polar-maritime facies in northern N o r w a y insufficient s u m m e r w a r m t h is the deciding factor, the winters being abnormally mild but rather dark a n d stormy. Besides, the occurrence of palses, i.e., peat hillocks with a n ice core (Figs.5 to 7), must be mentioned here. T h e y are the first precursors of real tundra only stretching farther east, uninterruptedly, over continuous

FIG. 4. Table birches (Betula tortuosa), some with tops, north of Karesuando (Lapland) (Bliithgen, 1936).

23

J. Blüthgen

permafrost and standing in evidence of the S u b arctic. This p h e n o m e n o n also is lacking in the other facies of the regio betulina including the polar-maritime facies. Palses very often have a weathered, dried-up s u m m i t where in a n otherwise boggy country often s o m e mountain birches have taken root. This could be observed by the present writer in 1936 o n the “bush cold steppes” which are mainly formed by Betula nana a n d several Salix species, between Karesuando and Kautokeino beyond the Finnish-Norwegian border, over a wide area so that the tree limit there w a s extremely scattered.

To the natural characteristics of the subarctic part of the regio betulina, m a n - m a d e factors m u s t b e added if w e w a n t to see the Subarctic with the whole scope of geography in mind. This region is pastured by reindeer ; these vagrant animals bite the birches a n d cause trampling damages o n dry locations (damages which often f o r m the starting-points for deflation effects) the subarctic m e a d o w s are used for keeping cows, goats, and sheep in scattered permanent settlements. Although the settlement density at the border of h u m a n settlement as a whole is extremely low (about 2-3lhuman beings o n 10 km2)the influence of h u m a n FIG.5. A group of small palses, i.e., peat hillocks with an ice core, near North Cape on Mageröy (Blüthgen,1960).

FIG.6. A rather big pals near Karlebotn (Varangerfjord, northern Norway) (Blüthgen, 1966).

24

Problems of definition and geographical differentiation of the Subarctic

economy, in the Subarctic, not only in northern Europe, is strongly marked. Despite all the technical improvements in m o d e r n h o m e s the d e m a n d for w o o d to build fisheries, enclosures a n d for heating is heavy because of the very slow gain and very far-between regeneration periods. Today’s picture of the bordering forests in the paraboreal subzone a n d the course of the tree and w o o d limit m u s t therefore be regarded as being influenced by m a n far m o r e than might appear at first sight of these apparently virgin and uninfluenced bordering stands. M a n y of the pine-free birch bush forests are likely to o w e their present appearance to the hewing of scattered pine tufts and of birch mother trees used for heating and making enclosures during the past centuries. T h e power to form sprout from the roots of Betula tortuosa has led, to the formation of multi-trunked trees similar to bushes (polycormia) which over large areas, for instance in inner F i n n m a r k and in Finnish Lapland, determines the appearance of the birch forests. This does not deny that there are natural factors as well which m a y lead to polycormia. T h e increase of settlements during the last decades, though slow, together with over-exploitation of the border forest during and reconstruction w o r k after the heavy damages of the Second World w a r have left w o u n d s which, at best, will be closed after m a n y decades, probably even centuries, by a natural regeneration of the forests. Perhaps continued damages and a final receding of the w o o d and tree limit in the paraboreal subzone must be reckoned with especially along the Barents Sea coast which is m o r e densely populated byfishing settlements. On the other h a n d s o m e afforestation (Fig.8, see also Mikola, 1969) with Scotch pine has taken place in northernmost Finnish Lapland near Utsjoki showing that at least s o m e recovering of devastated mixed birch a n d pine forest is observed at certain places under favourable local climatic conditions. B u t the annual average yield of wood, only in small favourable sites, exceeds 1 cm3/hectare, so that these stands are of n o perceptible economic value in comparison to m o r e southerly stands. In the settlements there is s o m e possibility for cultivating vegetables in greenhouses because of long daylight during the subarctic s u m m e r . B u t this is only of local importance though it helps to improve man’s diet. Finally I should like to set up the following theses which are a s u m m a r y of the results obtained and which m a y be regarded as important for the definition a n d differentiation of the subarctic. 1. T h e Subarctic forms a belt of its o w n between the arctic a n d the middle latitudes. It comprises a marine and a terrestrial part. B o t h m u s t b e defined separately. 2. T h e marine Subarctic is confined to the water areas o n both sides of polar convergences between

-

5-

+

o al

R

-3 0 ~ :m

-

>i

o

U C o) N

2

u-

-8 0 ~ :m

al U .L

-oal

-

U

100 cm

FIG.7. Section through upper part of apal near Karlebotn (Varangerfjord, northern Norway). The uppermost part of the section-some 30 cm-consists of peat, beneath follows frozen post-glacial clay mixed with clear ice near the lowermost part (approx. 1 m) (Bliithgen, 1966). polar a n d temperate sea water with seasonally shifting drift ice. 3. T h e terrestrial Subarctic lies between the arctic discontinuous patch tundra a n d the economic forest limit of the boreal coniferous forest belt (taiga). It thus comprises the plant-geographical areas of the continuous herbaceous tundra at the border of the Arctic, the boggy forest tundra, the northernmost facies of the Scandinavian mountain birch forest d o w n to the rational forest border along the northern periphery of the taiga where not m o r e than every fifth to tenth year is a year of seed ripening a n d where, therefore, there are larger breaks between t w o generations. T h e rational forest border, as it might b e called, is at the s a m e time nearly the limit of economic forest exploitation. 4. In agreement with Grigoriev the terrestrial Subarctic can b e subdivided into a pararctic (pa) and a paraboreal (pb) subzone.

25

J. Blüthgen

FIG. 8. Afforestation of Scotch pine in the mixed birch-pine forest south of Utsjoki near Petsikko, well-drained soil, but northern exposure. The group of young trees have suffered from frost damage in spring during one of the latter years (Blüthgen, 1966).

5. T h e pararctic subzone (pa) comprises the herbaceous tundra in its drier or m o r e h u m i d varieties. It is climatically characterized by average temperatures of the warmest m o n t h between 40 C and 80 C; the average temperature of the coldest m o n t h stays beneath -80 C. 6. T h e paraboreal sub-zone (pb) has a n oceanic and a continental variety. Within the continental area it can be divided into a northern (pbn) and a southern (pbs) belt. 7. T h e oceanic variety of the paraboreal subzone comprises the subpolar m e a d o w s with birch w o o d s in Alaska, south-west Greenland, and Iceland, the Atlantic part of the Scandinavian mountain birch forest north of about 680 N; warmest m o n t h 100 C to 120 C, coldest 20 C to O0 C, low amplitudes. 8. T h e northern belt of the continental variety of the paraboreal sub-zone (pbn) includes in northern Eurasia and North America the forest tundra and the Lapland part of the Scandinavian birch forest. T h e warmest m o n t h here shows 80 C to 100 C, the coldest stays below -80 C, the amplitudes are large, however. 9. T h e southern belt of the continental variety of the paraboreal subzone (pbs) is formed by the northern border forests of the taiga with open, often boggy stands beyond the rational (or reproductive) forest limit where, o n a n average seed ripening is possible only every fifth to tenth year. W a r m e s t m o n t h shows 100 C to 120 C, coldest likewise below -80 C, amplitudes are large here as well. 10. T h e continental Subarctic is characterized climatically by high unperiodic temperature oscillations. N o m o n t h is therefore quite free of frost but in the continental region the m a x i m a of the three s u m m e r months can approach 300 C.

26

11. T h e oceanic Subarctic has in fact lower oscillations but lower s u m m e r averages and therefore total heat is lower in summer. 12. T h e total heat gained by a positive s u m m e r radiation balance of about four months duration is sufficient to produce, after the melting of the s n o w a continuous vegetation cover which forms the habitat of a subarctic fauna adapted to these conditions (reindeer, polar fox, lemming, mosquitoes). 13. Absolute air humidity is very low, the relative humidity mostly high. S u m m e r is therefore foggy, especially near the Arctic Ocean. 14. T h e quantity of precipitation is mostly small a n d is mainly caused by advection activities following cyclonic fronts a n d occlusions rather than by convection, though this m a y occur in s o m e cases attached to labile weather type. Only in the oceanic regions, and there mostly in front of mountain ranges is precipitation relatively high. 15. Protection against wind and s n o w plays a vital part for the vegetation, as the s n o w cpver is mostly very uneven or thin and wind intensity-especially in late winter-is relatively high. 16. Permafrost is developed continuously everywhere in the pararctic subzone, a n d in the paraboreal, only in the continental parts. In the oceanic parts it occurs only in the peripheral form of interrupted peat hillocks with ice cores (palses) or is even lacking altogether where in the coldest m o n t h the temperatures is O0 C or immaterially below freezing-point a n d temperature oscillations are only short-lived and d o not lead to extreme frost periods. 17. T h e open solifluction, polygon soils, stone rings and areal formation of frost debris, typical of the Arctic, occur only sporadically in the Subarctic

Problems of definition and geographical differentiation of the Subarctic

FIG. 9. Solifluidal terraces under close vegetation cover on Mageröy (noirthern Norway) (Blüthgen, 1960).

because of the mostly continuous vegetation cover. Hidden flows of earth, however, under vegetation cover o n slopes (grass pads, fig. 9), and the occasional breaking up of these pads frequently occur. 18. T h e soil is cold in s u m m e f and superhumid; w a r m t h is sufficient only in a very thin surface layer of s o m e centimetres ; plants have therefore superficial roots and are adapted against too high evaporation by the xerophytic structure of their organs or by cushion growth or by both. Large areas in flat regions are rich in bogs of different kinds. 19. In the regional differentiation of the vegetation of the Subarctic according to associations, differences of local exposition and the differentiation of the microclimate near to the ground play the decisive part. 20. T h e shortness of the subarctic s u m m e r together with almost n o transitional seasons require that the sub-arctic vegetation prolongs its reproduction phases over several years, and that vegetative generation is widely found. However, growth is accelerated somew h a t during s u m m e r light conditions. 21. T h e Subarctic is the m a i n exploitation area of reindeer e c o n o m y in so far as the animals find the necessary nourishment, to build up stores of fat, o n the subarctic s u m m e r pastures. In the winter they feed on lichens in the protected border forests towards the taiga only in order to survive until the reopening of the s u m m e r pastures. 22. As the marine subarctic areas are rich in plankton a n d fish, due to the convergence a n d mixing of cold water rich in oxygen with w a r m e r water from the

south, the subarctic coasts along or near to these oceanic regions are characterized by densely inhabited fishing settlements in otherwise almost uninhabited surroundings. 23. Because of the slow and low increase of vegetation¶ man’s influence is extremely noticeable in the Subarctic even though it is sparsely populated. Changes in the subarctic vegetation cover are mainly d u e to the following factors: pines are receding and occur within the birch region; a birch forest is forming d u e to the m o r e bushy appearance of the stands because trees sprout from the roots ; overgrazing by too m a n y herds of reindeer; the coastal settlements’ d e m a n d for w o o d for heating purposes and building enclosures; also, locally, the appearances of natural m e a d o w s is changed as a result of the intensive haymaking in s u m m e r to meet the needs of the increasing c o w staple. . Summing up this tentative definition leads to a n extension of terrestrial a n d marine subarctic areas which m a y be seen in Figure 10.

ACKNOWLEDGEMENTS I

wish to express m y sincere thanks for technical assistance and discussion to my collaborators, R. Lind e r m a n n a n d D. Thannheiser, a n d to mention here m y late friend Hans-Günther Sternberg, fellow of m a n y discussions o n a n d of journeys through the Scandinavian Subarctic.

27

160'

\

FIG.10. M a p of the subarctic and its sub-division (compiled by J. Bliithgen).

Pararctic

Terrestrial Subarctic

Northern

14c

Paraborea I Sou thern , ,

Rational forest limit Marine Subarctic (seasonal shifting sea-ice)

r-.

Mountainous vegetation within the Subarctic

m,

Paratemperate (polar radiation régime in temperate oceanic regions with positive temperature anomaly)

VmJ 4 :

aracontinental (polar radiation . regime in boreal regions)

120'

1000

/

1 O00

e00

60°

LOO

O ,

500 '

,

B

.

,

1000

1500

2000 krn 1

J. Blütbgen

Résumé Problemes de déjnition et de différenciationgéographique du Subarctique, spécialement en Europe septentrionale (J. Bliithgen)

.

L a région subarctique est une zone de paysages située entre l’Arctique et la forêt boréale de conifères; c’est la zone phytogéographique de la toundra herbacée continue qui s’étend de la limite de l’Arctique jusqu’à la région forestière limitrophe du nord de la taïga, où plus d’une année sur d e u x permet la maturation des graines et où il n’y a, par conséquent, pas d’interruption plus grande entre d e u x cycles végétatifs. L a région subarctique comprend diverses sous-zones : continentale et océanique, d’une part, et para-arctique et paraboréale, d’autre part. L a sous-zone subarctique continentale se caractérise climatiquement par de fortes oscillations n o n périodiques de température. A u c u n mois n’y est donc sans gel; mais les m a x i m u m s des trois mois d’été peuvent s’approcher de 300. D a n s la sous-zone subarctique océanique, les oscillations de température sont moins fortes, mais par contre les moyennes estivales sont plus faibles, si bien que les s o m m e s thermiques y sont moindres. L a s o m m e thermique fournie par le bilan radiatif positif d’un été d’environ quatre mois est suffisante pour donner après la fonte de la neige une couverture végétale continue qui constitue l’habitat d’une faune subarctique adaptée à ces conditions (renne, lemming, moustiques). L’humidité absolue de l’atmosphère est très faible; l’humidité relative est le plus souvent élevée. L’été

est donc brumeux. Les précipitations sont généralem e n t faibles et résultent des m o u v e m e n t s d’advection consécutifs a u x fronts cycloniques et a u x occlusions. C e n’est que dans la région océanique, n o t a m m e n t sur le versant des chaînes montagneuses, que les précipitations sont relativement fortes. L e pergélisol est continu dans toute la sous-zone para-arctique et, dans la sous-zone paraboréale, seulement dans les parties continentales. D a n s les parties océaniques, il est discontinu. L a solifluction caractérisée, les sols polygonaux, les cercles de pierres et la formation aérolaire de débris produits par le froid n e s’observent qu’occasionnellement dans la région subarctique. L e sol est froid l’été; les végétaux hygrophiles ont donc des racines superficielles et l’adaptation les protège contre une évaporation trop forte. D a n s la différenciation régionale de la végétation subarctique selon les associations, l’exposition locale et le microclimat (près d u sol) jouent u n rôle décisif. Par suite de la brièveté de l’été subarctique et de l’absence presque complète de saisons de transition, la végétation subarctique doit étendre son cycle de reproduction sur plusieurs années ; en outre, la reproduction végétative est très répandue. P a r m i les principales ressources naturelles renouvelables de la région subarctique, o n peut citer le renne, ainsi que les poissons des zones océaniques riches en plancton. D u fait de la lenteur et de la faiblesse de l’accroissement végétatif dans la région subarctique, l’influence de l’homme y est extrêmement marquée.

Uiscusssion J. MALAURIE. Après le remarquable exposé du professeur Bliithgen, il est souhaité que le congrès aille, sur le plan épistémologique, plus avant, c’est-à-direrecherche la structure logique -indispensable à toute doctrine scientifique -de ce terme “ subarctique”, terme prêtant à des analogies spécieuses et à quelque ambiguïté. Sur le plan géomorphologique, d‘autre part, des définitions quelque peu différentes pourraient être apportées aux limites présentées, surtout phytogéographiques. J’y reviendrai plus loin dans ma communication; mais nombreux sont les faciès subarctiques dans les plateaux du nord-ouest du Groenland, haut arctique. D’autre part, comment, génétiquement, sur le plan géographique, définir une forme subarctique, alors m ê m e que, dans les roches résistantes, les formes sont le plus souvent polygéniques. Les formes spécfiquement, originellement “arctiques” n’ont été observées que dans les roches “meubles” de la terre d’hglefield (nord-ouest du Groenland). Le terme “toundras”, d’après une toute récente publication

30

de Donald A. Dagon (Polar notes, no 6,juin 1966), ayant été redéfini également “structurellement”, il est souhaité que le congrès saisisse en vérité l’occasion de ce rassemblement d‘experts pour constituer rapidement une commission “interdisciplinaire” visant à tenter de mieux définir le t e r m e “subarctique”; dans m o n esprit, voire m a formation de géomorphologue, ce terme a seulement valeur “topologique”. Ce serait avec plaisir que je participerais à ces travaux. A u moment m ê m e où la recherche polaire se développe si rapidement,il serait vraiment regrettable que se développent entre spécialistes des malentendus, fruits d’écoles, d’approches multiples, dans l’utilisation de ce terme. J e rappellerai seulement ce bien fâcheux vocable “périglaciaire”, source de si vives controverses, et toujours, dans son acception “boréale”, bien vivant.

J. B L ~ T H G E N .The problem of defining the subarctic is so complex that the proposal to discuss it between members of an interdisciplinaly commission is an excellent idea.

Problems of definition and geographical differentiation of the Subarctic

E. EINARSSON. O n page 16 Dr. Blüthgen gives a definition of a “subarctic tundra climate” and “subpolar, high oceanic climate”. According to that definition North Iceland has a “subpolar, high oceanic climate” not a “subarctic tundra climate” as stated in the paper. All the Icelandic lowlands have a “subpolar, high oceanic climate”, the mountain areas, however, especially in the central part of the country have a “subarctic tundra climate”.

T h e main report dealing with the variation J. BL~THGEN. of opening of stomata during periods of dryness (or warmth) relied upon is Stocker’s, Darmstadt, w h o has studied the vegetation of Swedish Lapland near Abisko. This is in agreement with xerophylism of m a n y subarctic and arctic plants which in this way are adapted to variations in humidity.

E. HULTEN. In your m a p of the Subarctic you had marked J. BL~THGEN. That is a correction which miist be followed up; in literature the classification of Iceland as subarctic 01 otherwise is rather contradictory. In the first part of m y paper I cited some of these contradictory statements. T. AHTI. I would like to point out that, from the point oi view of comparative circumpolar ecology, tree species m a y be poor indicators of the Arctic and the subarctic in some areas when compared to lesser vegetation, particularly byophytes and fungi, including lichens, the distribution of which has been m u c h less affected and interrupted b y the post-glacial vicissitudes. Perhaps, with these criteria, the Subarctic m a y be distinguished even in Iceland, Greenland and the Aleutian Islands. Of course, it depends on which criteria are given preference. Another more objective criterion for comparison of different areas is, of course, climatic measurements.

J. BL~THGEN. Thank YGU for adding these biological factors to define the Subarctic. A geographical definition of “Subarctic” must of course rely on as m a n y statements from related sciences as possible.

south-western Alaska and the Aleutian Islands with a special dark green colour. I carried out field work in that area last summer. T h e flat ground is an arctic tundra with the same plant communities as on the Arctic Slope of Alaska and with numerous lakes. There is no reason to regard this area as a separate division of the Subarctic, it is an arctic district. Concerning the Aleutian Islands the question is more complicated as they are very mountainous, but they are all completely treeless.

J. BL~THGEN. The dark green colour in south-western Alaska and on the Aleutian Islands represents oceanic “subpolar meadows” after the detailed maps in the Physicogeographical World Atlas (c 1964) from Moscow. S o m e earlier authors also used the term “subpolar meadows” with respect to subarctic regions of high oceanic climate. Thank you for your comment based on pour field observations. Perhaps the term “subpolar meadows” must thus be abondoned in subarctic regions, because even Iceland, hitherto often classified as a land of “subpolar meadows” has been deprived of most of its birch wood in lower districts by man.

R. SARVAS.W h e n considering the definition of the subF. E . ECKARDT. J’ai suivi avec grand intérêt votre exposé, en particulier pour ce qui concerne le comportement physiologique des plantes pendant les périodes de dégel et de sécheresse estivale. Vous avez mentionné à u n certain moment que les plantes ferment les stomates en vue de réduire les pertes hydriques (page 7 du document miméographié). Pourriez-vous m’indiquer les travaux sur lesquels ont été basées ces observations ? Je pose la question parce que j’ai eu l‘occasion personnellement de mesurer la transpiration de trois espèces végétales, à savoir Salix glauca, Vaccinium uliginosum var. microcarpa et Betula nana, au Groenland, pendant l’été. Ces mesures ont été effectuées dans les régions particulièrement sèches de Söndre Strömfiord et de Thulé (précipitations annuelles de l’ordre de 60-70 mm). Au cours de ces études je n’ai jamais p u constater la moindre augmentation dans la résistance diffusive des stomates, la courbe journalière de transpiration ayant pratiquement la m ê m e allure que celle de l’évaporation potentielle mesurée au moyen d’un disque de papier buvard mouillé.

arctic region, there is reason to keep in mind for what purpose the definition is to be used. W h e n it is mainly used to arrange data already available and to make large general surveys, syntheses, there is undoubtedly reason to use a definition of great coverage, even as large as to be able to serve several branches of research, such as, for instance, meteorology, phytogeography, geology, forestry, etc. When, however, n e w information is required, the most important thing is that the definition serves the unravelling of the actual problem in the best way possible. It can often be useful to work out one definition of the subarctic region to be used for the solving of one single problem. Perhaps, however, a feature c o m m o n to all these definitions could be that the sub-arctic region is formed b y an area, where, from the point of view of the problem or object in question, an arctic influence is more or less to be noticed. O n the basis of this, I suppose that there will always be several definitions, some of which serve primarly the synthesis and others the analysis.

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720 p. (Lehrbuch d. Allg. Geogr., edited by E. Obst, Vol. II.) BROWN, R. J. E. 1969.Permafrost as an ecological factor in the Subarctic. Ecology of the subarctic regions. Proceedings of the Helsinki symposium / Écologie des régions subarctiques. Actes du colloque d’Helsinki. Paris, Unesco. (Ecology and conservation / Ecologie et conservation, I.) BUDYKO, M. I. 1955. Teplovoy balans zemnoy poverknosti. Leningrad Atlas. CREUTZBURG, N. ;HABBE, K.A. 1966.Klimatypen der Erde, M a p 1: 50,000,000.In: J. Blüthgen, Allgemeine Klimageogfaphie,2nd ed. DIETRICH, G. ; KALLEK. Allgemeine Meereskunde. Berlin. 492 p. (See also G.Dietrich, 1964.Ozeanographie. Braunschweig, 94 p.) DOLGIN, I. M. 1969. Sub-arctic meteorology. Ecology of the subarctic regions. Proceedings of the Helsinki symposium Ecologie des régions subarctiques. Actes du colloque d’Helsinki. Paris, Unesco. (Ecology and conservation / Écologie et conservation, I.) EKMAN, S. 1922.Djurvärldens utbredningshisïoriap i Skandinaviska Halvön. Stockholm, 614 p.) . 1944. Djur i de svenska fjällen. Stockholm, 428 p. (STFshandböcker o m det svenska fjället, vol. 3.) ENGLER, A.; DRUDEO. 1896-1928.Die Vegetation der Eide, vol. I-XV.Leipzig. FLOHN, H. 1950. Neue Anschauungen über die Allgemeine Zirkulation der Atmosphäre und ihre klimatische Bedeutung. Erdkunde, vol. 4,p. 141-162. --. 1951.Grundzüge der atmosphärischen Zirkulation und Klimagürtel. Wiss. Abh. Dt. Geogr.-Tag Frankfurt,p. 105-

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118. FORMOZOV,N. A. 1969.Écologie des plus importantes espèces de la faune subarctique./ Ecology of the subarctic regions. Proceedings of the Helsinki symposium / Écologie des régions subarctiques. Actes du colloque d’Helsinki. Paris, Unesco. (Ecology and conservation / Écologie et conservation I.) FRIES, Th. C. E. 1913.Botanische Untersuchungen im nöidlichsten Schweden. Ein Beitrag zur Kenntnis der alpinen und subalpinen Vegetation in Torne Lappmark. Uppsala. 361 p. GRIGORIEV,A. A. 1956.Subarktika. 2nd ed. Moscow. 223 p. HÄMETT-AHTI, L. 1963.Zonation of the mountain birch forests

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in northernmost Fennoscandia. Helsinki. 127 p. (Ann. Bot. Soc. Zool. Bot. Fenn. Vanamo, vol. 34,no. 4.) HARE, F. K. 1950.Climate and zonal divisions of the boreal forest formation in eastern Canada. Geogr. Rev., vol. 40, p. 615-635. HASSINGER,H . 1933.Die Geographie des Menschen (Anthropogeographie). In: F. Klute (ed.), Handb. d. Geogr. Wiss. vol. Allg. Geographie II. Potsdam. p. 167-542. HETTNER, A. 1930. Die Klimate der Erde. Leipzig, Berlin. 115 p. (Geogr. Schriften, vol. 5.) . 1935. Die Pflanzenwelt. Vergleichende Länderkunde, vol. IV, part 5,p. 1-153.Berlin, Leipzig. HULTÉN, E. 1950.Atlas över växternas utbiedning i Norden1 Atlas of the distribution of vascular plants in N W . Europe. Stockholm. 512 p. . 1962. The circumpolar plants. I. Vascular cryptogams, conifers, monocotyledons. Stockholm. 275 p. (Kgl. Av. Vet.-Ak. Handl., Ser. IV vol. 8,no. 5.) HUBTICH, 1. 1939. Notes on the coniferous forest and tree limit in the east of Newfoundland-Labrador. Acta geogr., vol. VII, no. 1, p. 1-77.. . 1950. Notes on the forests on the east coast of Hudson Bay and James Bay. Acta geogr.,vol. XI, no. 1,p. 1-83. . 1958. On the recent expansion of the Scotch pine in northern Europe. Fennia, vol. 82,no. 3,p. 1-25. HUSTICH, I. 1960. Plant geographical regions. In: A. S ö m m e (ed.), A geography of Norden. Oslo. p. 54-62. . 1966.O n the forest-tundra and the northern tree limit. Ann. Uniu. Turku, vol. A, II, 36,41 p. (Reports from the Kevo Sub-arctic Research Station, vol. I.) KALELA, O. 1961.Seasonal change:of habitat in the Norwegian lemming, L e m m u s lemmus (L.).Helsinki, 72 p. (Ann. Acad. Scient. Fennicae, Ser. A, IV, vol. 55.) . 1963.Beiträge zur Biologie des Waldlemmings, Myopus schisticolor (Lillj.) Helsinki, 96 p. (Arch. Soc. Zool. Bot. Fenn. Vanamo, Suppl. 18.) KALLIO, P. 1964. The Kevo Subarctic Research Station of the University of Turku. Ann. Uniu. Turku, vol. A, II, 32,p. 9-40.(Reports from the Kevo Subarctic Research Station, vol. I.) KIHLMAN, A. O. 1890. Pflanzenbiologische Studien aus Russisch Lappland. Helsinki. 256 p. (Acta Soc. Fauna Flora Fenn., vol. VI, 3.) KIMBLE, G. H . T.; DOOD, D. (eds.). 1955. Geography of the Northlands. New York. 534 p. (Amer. Geogr. Soc., Special publ. no. 32.) KNAPP, R. 1965.Die Vegetation von Nord- und Mittelamerika und der Hawaii-Inseln.Stuttgart.373 p. KOPPEN, W.1900.Versuch einer Klassifikation der Klimate vorzugsweise nach ihren Beziehungen zur Pflanzenwelt. Geogr. Zeitschr., vol. 6,p. 593-611; 657-679. . 1918. Klassifikation der Klimate nach Temperatur, vol. 64, Niederschlag und Jahreslauf. Peterm. Geogr. Mitt., p. 193-203;243-248. . 1923,1931.Die Klimate der Erde. Grundriss der Klimakunde. Berlin, Leipzig. 369 p.; 2nd edition under the title: Grundriss der Klimakunde. Berlin, Leipzig, 1931, 388 p. ; GEIGER, R . 1928,1961. Klima der Erde -Climate of the earth. (Wall-map 1: 16,000,000.1st ed., Gotha, 1928; 3rd., Darmstadt, 1961.)

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L EMBHE, H . 1947. Die mittleren absoluten Maximaltemperaturen in Europa und den Mittelmeerländern. Erkunde, VOL 1, p. 184-189.) LUNDEGARDH, H . 1957. Klima und Boden in ihrer Wirkung auf das Pflanzenleben. Jena, 584 p. MIKOLA, P. 1969. Forests and forestry in subarctic regions. Ecology of the sub-arctic regions. Proceedings of the Helsinki symposium / Écologie des régions subarctiques. Actes du colloque d’Helsinki.Paris, Unesco (Ecology and conservation / Ecoiogie et conservation, I.) PASSARGE, S. 1921. Vergleichende Landschaftskunde. II. Kältewiisten und Kältesteppen. Berlin. 163 p. . 1923. Die Landschaftsgiirtel der Erde. Breslau. 144 p. PHILIPPSON, A. 1931, 1933. Grundziige der Allgemeinen Geographie. Vol. I, 2nd ed., Leipzig, 1933, 379 p.; vol. II, 2nd ed., Leipzig, 1931, 551 p. RITCHIE,J. C. 1960. The vegetation of northern Manitoba. Arctic, vol. 13, p. 211-229. ROUSSEAU, J. 1952. Les zones biologiques de la péninsule Québec-Labrador et l’hémoarctique. Canad. J. Bot., vol. 30, p. 436-474. . 1964. Coupe biogéographique et ethnobiologique de la péninsule Québec-Labrador. Vol. 2, p. 29-94. Paris. Ecole Pratique des Hautes Etudes à la Sorbonne, VIe section, Québec-Labrador et l’hémoarctique. Canad. Bot., vol. 30, p. 436-474. . 1964. Coupe biogéographique et éthnobiologique de la péninsule Québec-Labrador. Vol. 2, p. 29-94. École Pratique des Hautes Etudes à la Sorbonne, VIe section, Bibliothèque arctique et antarctique. SCHMITH~SEN,J. 1961. Allgemeine Vegetationsgeographie. Berlin. 262 p. (Lehrbuch d. Allg. Geogr., ed. by E.Obst, vol. IV.) SCHOTT, G. 1942. Geographie des Atlantischen Ozeans. 3rd ed. Hamburg. 438 p.

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_- . 1965. Forest regions. In: The plant cover of Sweden. p. 48-63.Acta phytogeogr. suecica,vol. 50. TIKHOMIROV, B. A. 1960. Plantgeographical investigations of the tundra vegetation in the Soviet Union. Canad. J. Bût., vol. 38, p. 815-832. . 1967. Environment and the mode of plant adaptation to it in the Far North of U S S R . Oulon University, Finland Aquilo, Söyrinki’s Jubilee volume. TREWARTHA, G. T. 1954. A n introduction to climate. 3rd ed. London. 402 p. TROLL, C. 1941. Studien zur vergleichenden Geographie der Hochgebirge der Erde. Ber. 23. Hauptvers. Ges. Freunde u. Förderer Rhein. Fr.-Wi1h.-Uniu.Bonn, p. 49-96. . 1959. Die tropischen Gebirge. Ihre dreidimensionale klimatische und pflanzengeographische Zonierung. Bonn. 93 p. (Bonner Geogr. Abh. vol. 25.) .1965. Jahreszeitenklimate der Erde. D e r jahreszeitliche Ablauf des Naturgeschehens in den verschiedentn Klimagürteln der Erde/Seasonal climates of the earth. The seasonal course of natural phenomena in the different climatic zones of the earth. With m a p 1: 45 Mill. by C. Troll and K . H.Paffen: Jahreseeitenklimate der Erde / Seasonal climates of the earth. In: Weltkarten zur Klimakunde / World maps of climatology.2nd ed., p. 7-28.Berlin, Göttingen, Heidelberg: the coloured m a p also in J. Blüthgen, 1966, Allgemeine Klimageographie. WAHLENBERG, G. 1812. Flora lapponica. Berlin. 550 p. WALTER, H . 1954. Einführung in die Phytologie. III: Grundlagen der Pflanzenverbreitung. Einführung in die Pflanzengeographie. 2nd. part Arealkunde (Floristisch-historische Geobotanik). Stuttgart. 245 p. W I S S M A N N ,H . von. 1966. Die Klimate der Erde. M a p 1: 50 Mill. In: J. Blüthgen, 1966. Allgemeine Klimageographie.

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Forest limits as the most important biogeographical boundarvJ in the North B. A. Tikhomirov

The transitional,boundary belts or limits are inherent in every geographical phenomenon ; but the biogeographical limits have their o w n specific features. They are characterized, as a rule, by the complexity of the boundary line, the gradual transition1 from one biological complex to the others, the degradation of its typical features and gradual development of others. Here, besides the changes in the indices of the abiotic medium (climate, relief, soil, humidity, etc.) the complicated mechanism of interrelations between organisms and their relations with the medium interferes with the biogeocenological process which lies behind the population inconstancy of plant c o m m u nities. In this intricate complex-the complexity of which is not open to doubt-the important role belongs to the peculiarities of organisms and in the first place their capability for reconstruction and for the adaptive reactions, connected with the changeability and with the relative stability of the medium. The process of the adaptation of organisms to the changing and severe medium at their areas’ limits depends first on the hereditary basis of the organisms, the amplitude of intraspecific variability of the hybridogenous processes and also on the degree of influence of the external factors. Proceeding from these general presumptions let us examine the forest limits as the most important biogeographical limit in the North. Without going into details of the history of the development of this problem, it is worth mentioning that the problems of the forest7slimits,its characteristics, and dynamics, the interrelations between the forest and the tundra and the reasons for the absence of trees from the tundra called the attention of northern Russians and U.S.S.R. explorers more than a century ago. Scientists such as Maidel (1894), Kihlm a n (1890), Schrenk (1855), Middendorf (1867), Tanfil’ev (1911), Pohle (1903, 1917), Grigor’ev (19241,

’

Kaminsky (1924), Gorodkov (1929),Tsinzerling (1932), Tolmachev (1931), Sochava (1940), Leskov (1940), Govorukhin (1947,1956, 1963), Tyulina (1936, 1937), Medvedev (1943, 19521, Leont’ev (1948), Andreyev (1956),Tikhomirov (1953,1956,1962),Tyrtikov (1954), Norin (1961, 1962), Vasskovsky (1958), Kr’uchkov (1963),Yurtsev (1962, 1966), and others have made their contributions to this problem.2 It should be mentioned that several scientists in other countries also touched on these questions (Griezebakh, 1874; Hein, 1932; Nordenskjold, 1882 ; Roder, 1895; Wigge, 1927, and others), but special attention has been drawn during the last two decades to Hare (1950), Hustich (1939, 1950, 1953), Sjors (1963), Rousseau (1952), Sigafoos (1958), Hopkins (1959), Johansen (19631, R o w e (1959), Savile (1963), and others. A comprehensive analysis of the natural conditions influencing the northern forest limits is the main feature of such studies in the U.C.S.R. Lately the necessity of such complex analysis of factors is recognized also by a number of forest-limit investigators in other countries (Hustich,1953; Savile, 1963, and others). The maps of the northern limits of trees have already been made (Hustich, 1953; Tikhomirov, 1962; Vasskovsky, 1958, and others) and there is no need to discuss this problem, for the new data add nothing to the codguration of their areas. For the analysis of botanic-geographical relations in the Subarctic not only is it important to ascertain the northern limits of trees, but also, mainly, the characteristics of the nearly circumpolar transitional 1. This doee not except the sharp limite when Nome biological complexes pa6s into others in connexion with sharp changes in relief, humidity and other external fsctors. 2. Recently, the interest in these problems in the U.S.S.R.w a s especially increased in connexion with the problem of afforestationof the southern parte of the tundra and the preservation of the northern forest limits.

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B. A. Tikhomirov

belt between the northern taiga and the tundra. This belt c a m e into Russian literature after the second part of the nineteenth century under the n a m e of lesotundru (“forest-tundra” in English “Wald-tundra” in German).l T h e forest-tundra m a y be a good example of a transitional biogeographic boundary, limit or belt of the Earth. I would like to mention s o m e general features of forest-tundra, as a world-wide biogeographical phenomenon. First its circumpolar distribution is noteworthy. T h e forest-tundra represents a zonal natural p h e n o m e n o n caused by the zonal climatic factors. As is generally k n o w n , the m a i n factor responsible for the zonal p h e n o m e n a o n the Earth is the uneven flow of solar heat energy to the different parts of the Earth’s surface. This factor resulting in zonality is inevitable. All other factors influencing the character of zonality merely intensify or distort its display o n the Earth. In particular, the botanic-geographical correlation of the northern Eurasian a n d northern American continents, as well as of the islands bordering o n them, is greatly influenced by the Arctic Ocean ice and the process of its melting. It is enough to mention that the ice area in the Arctic Ocean reaches 8.8 million km2 in winter with only 800,000 km2 less in s u m m e r (Zubov, 1945). T h e heat expended o n thawing of the ice, a n d the cold and humid winds blowing o n to the continent from the north, create unfavourable thermal conditions o n the land. O n e m a y recall the fact that the forest border runs parallel to the Arctic O c e a n shores :on the protruding part of the T a i m y r Peninsula are found the northernmost forest outposts (72040‘N.). On the contrary, the invasion of cold arctic water a n d ice into the H u d s o n Bay, as well as the long time during which the ice actually remains in the bay, bring the northern forest limit as low as 500 N. T h u s the difference between these t w o geographical limits o n the Earth, i.e., the northern forest limit and the southern tundra-limits, amounts to m o r e than 200 of latitude. In other parts of the world the northern forest limit, going generally parallel to the ocean shore-line,oscillates from 720 30’N. (lower reaches of the L e n a river) to 580 55‘ N. (the shore of the Okhotsk Sea). So the ice regions of the Arctic Ocean, the regimes of sea currents governing the water temperature, the processes of surface water evaporation and, finally, the air currents having their origin in the polar basin, form the complex of factors which play a very important role in fixing the limits of the northern forests. 1,ong ago one considered the forest limits to be roughly coincident with the July isoterm of 100 C as well as with the “isoline of K a m i n s k y ” representing the southern limits of areas with a relative humidity in day-time, in s u m m e r , of > 70 per cent. But in connexion with the m o r e detailed study of forest limits, of their configuration a n d also with the careful

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study of climate regime characteristics in the north, considerable diversity between these lines can be found despite their general coincidence. Still m o r e careful studies a n d confrontations are necessary a n d these are being carried out partly by Hopkins for Alaska. T h e northern forest limit takes m a n y forms a n d it is likely that it follows the biocenological complex not as yet considered which corresponds best to the nature of the different species, forms and populations of trees. Again, the general factors restricting the development of forests in the north being deterioration of the temperature regime a n d shortening of the w a r m season, there is quite a complex of factors which determine the local microclimatic and ecological conditions which either favour the formation of forest communities or restrict their development. A m o n g the factors restricting the vitality of trees and limiting their northern boundary the following m u s t be mentioned : meso- a n d microclimate, permafrost and the initial process of soil formation, biocenotic factors (the influence of different autotrophic and heterotrophic plants and animals), biology and ecology of trees (biornorphs, fruiting process, the vitality of seeds, the survival of seedlings, etc.). Finally w e must mention the influence of m a n a n d domestic animals, this latter proving to b e a decisive factor in s o m e districts. Examining the structure of forest-tundra c o m m u nities in the old a n d the n e w world as well, one m u s t not forget that the m a i n feature which distinguishes t h e m from the northern taiga is the disturbance of cenotic entity or the loss of the role of edscators by trees. O n e must bear in mind that the loss of determinating role by the tree cover leads to s o m e “phytocenotic unsaturation” of habitats which leads, together with the solifluction a n d spot-forming processes (although weakened in the forest-tundra), to the introduction of boreal and arctic elements and to the formation of “mixed” forest-tundra flora. Despite the climatic deterioration in the foresttundra as compared with the taiga, it also possesses s o m e factors favourable to plant life. T h e absence of a dense tree canopy in forest-tundra enables the development of relatively high productive lichen communities which form the m a i n basis of the reindeer industry. It is k n o w n that the predominant part of lesotundru territory (85-90per cent) in the U.S.S.R.is covered with reindeer pastures. There are s o m e data showing that the fruit productivity by the berryshrubs is s o m e w h a t higher in the forest-tundra as compared with the taiga. 1. T h e concept of lesotundro as well as the views of Russian and Soviet scientists on its boundaries have been expresaed b y B. N. Norin (1961) in his paper. “Whet is the ‘lesotundra’?”.Therefore w e will not dwell upon these problems here. Many Soviet scientists are n o w inclined to distinguish forest-tundra as a separate “forest-tundra zone”, which includes the belt of northern parkland forests from the south and the belt of shruh-tundra from the north.

Forest limits as the most important biogeographical boundary in the North

Also the n e w data of Rodin and Basilevitch (Basilevich and Rodin, 1964; Rodin and Basilevich, 1965) reveal the considerable reserves of organic matter in the litter of forest-tundra communities. It is a good source of nitrogen. H o w e v e r the forest-tundra belt differs sufficiently from the treeless tundra in its life condition complex. W i n d s of great velocity (often the storms m o v e at 35 m/s) prevail in the tundra while in forest-tundra they are abated by separately standing trees. T h e m e a n annual wind velocity in the forest-tundra is 6 m/s, increasing in the tundra to 8 m/s. In the tundra the poor s n o w cover is thickened by the strong winds and reaches a compactness which restricts the use of under-snow fodder by reindeer. In the forest-tundra the s n o w cover, although thicker, is friable, making fodder m o r e accessible. T h e air temperature is higher in the forest-tundra. W h e r e s u m m e r thawing of the ground layer is thicker, the microbiological processes are m o r e active and result in the formation of comparatively m o r e fertile soil. T h e latter brings about a m o r e vigorous vegetation. Owing to the above-mentioned differences between the natural conditions of tundra a n d foresttundra the life conditions for plants in t h e m differ considerably. Also the conditions for animals are rather unfavourable in winter whereas the forest-tundra in winter is the life area of numerous animals. It must not b e forgotten that open-ground agriculis connected to a certain extent ture in the U.S.S.R. with the northern forest and parkland boundary. So it is of importance to emphasize that the forest limits and the forest-tundra belt itself represent a very significant biogeographical boundary a n d is also of paramount importance for the people’s economy. It is k n o w n that the life a n d e c o n o m y of m o r e than twenty aboriginal peoples are closely connected with the northern taiga parklands, the forest-tundra a n d its outpost. O n e of the lesotundra characteristics is the peculiarity of w o o d y plant biomorphs, this being circumpolar also. In the north the trees lose their usual form with a n orthotropically growing trunk, it being replaced there by the different modifications of this biomorph (such as trees with plagiotropically or semi-plagiotropically oriented stems, trees with curved tops, flag-shaped forms, bow-trunked ones, khodylni, “trees in skirts”, semi-prostrate or prostrate trees, table-shaped a n d trellis-shaped forms, literally growing into the moss cover (Larix dahurica,for instance). T h e c o m m u n i t y of biomorphs all over the circumpolar area of forest-tundraindicates the approximately similar natural influences o n the different tree species and nearly equal response of organisms to these influences in all parts of it. Considering the forest-tundra as a world-wide botanic-geographical p h e n o m e n o n w e must note the

various cenomorphological structures of its c o m m u nities in the Old and the N e w World, which are rather alike w h e n compared with each other. T h e parklands (redkoles’ja),forest islets, well-spaced trees with their various morphological forms, all are extremely alike in the forest-tundras of both the Old and the N e w World. There is n o doubt that a careful and detailed analysis of the structure and composition of plant communities would result in the revelation of m a n y features both of similarity and of difference. T h e latter depends first and foremost o n the fact that the forest limit is formed by different tree species in different parts of the world. In the Atlantic Arctic the meadow-forests of Betula tortuosa are widely distributed; o n the sand soils without permafrosts Pinus silvestris forms the forest limit. In the north of the European part of the U.S.S.R., side by side with birch, the following c o m munities grow in the forest-tundra: Picea abies (western section), Picea o bovata and Larix sukaczevii (eastern section), a n d in western Siberia, Larix sibirica which is replaced by Larix dahurica east of the Jenissey. T h e last species forms the northern forest limit throughout all eastern Siberia. H o w e v e r in Translenian Siberia the pattern of the northern forest is interspersed with Pinus pumila in the mountain habitats and with Chosenia macrolepis and Populus suaveolens in the valleys. These trees of angaroberingian origin give distinction to the forest communities of the north-eastern U.S.S.R.In the north of the n e w world w e meet with that specific group of trees which forms the northern forest limits. Picea glauca m o v e s northward along the well drained habitats and, as w a s recently shown, does not lose its normal shape up to the northern limits. Picea mariana is distributed over the wet habitats, the bogs; in the north it has a shrubshape. T h e northern limits of w o o d y vegetation are also reached by Larix laricina. It has a very wide ecological range, inhabiting s w a m p s a n d sand dunes as well, where it forms the lichen-larix communities greatly resembling the North Siberian larix forests (bory) composed of Larix sibirica. Proceeding from the analysis of the above-mentioned data, the necessity arises for dividing the forest-tundra belt of the Earth into sectors or segments according to the trees which form the forest limit of the areas. T h e forest limit as well as the width of the forest-tundra belt did not remain stable during the Quaternary period, the Post-glacial in particular. T h e dynamics of the northern biogeographical limits has been discussed repeatedly (Griggs, 1934 ; Tyulina, 1936, 1937 ; Tikhomirov, 1953 ; Andreyev, 1954, 1956 ; Hopkins, 1959, and others) and there is n o need to dwell o n this question. Let us point out however, that all the data concerning several decades of forest advance into the tundra must be carefully studied

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B. A. Tikhomirov

a n d used to elaborate the theory of the forest-tundra biogeocenoses transformation under the climatic amelioration. T h e necessity of forest plantations in the forest-tundra a n d in the southern tundra has b e c o m e imminent. T h e theoretical possibility of overcoming the absence of trees in the tundra is being translated into reality by the creation of tundra shelter belts. I would like to end the present report with a brief enumeration of the m a i n tasks confronting those investigating the problems of forest-tundra a n d forest a n d tundra interrelations: 1. T h e determination of “forest-tundra’’ (lesotundra) and “parkland” (redkoles )je) conceptions and the geographical boundaries of these types of vegetation. T h e detailed geobotanical characteristics of the different parts of the forest-tundra. 2. T h e biological peculiarities of the m a i n northern trees at their northern limits and defining exactly their t a x o n o m y and distribution limits. 3. T h e characteristics of the structural-biocenotical connexions in different plant communities of forest-tundra and forest boundary (insular treegroves, groups of shrubs, mosses, lichens, herbaceous plants). In particular the bioecological, phytocenological a n d climatological characteristics of forest-margins o n the northernmost outposts of forest with the a i m of revealing their role in the conquest of tundra by forest. 4. T h e role of animals in the life of forest-tundra,in the dynamics of the northern limits of forests and the study of this role (organization of complex biogeocenological investigations). 5. T h e elucidation of the ecologic-physiological, biological and cenological reasons for the absence

of trees from the tundra with extensive experiments at the northern forest limits. 6. T h e elucidation of man’s role in the dynamics of the northern limits of trees and forest-communities. 7. T h e elucidation of the history of the forest-tundra vegetation on the basis of palaeobotanical data. 8. T h e study of forest-tundra peculiarities in connexion with the origin of hypoarctic elements and forest limits’ m o v e m e n t in post-glacial times. 9. T h e plant resources of forest-tundra and the w a y s of making rational use of them. 10. T h e problem of forest preservation at the extreme limit. T h e precise fixation of separate forest islands in the tundra with a view to their preservation and observation. T h e organization of strictly reasoned out biological “bench-marks”, and of a n u m b e r of reservations a n d forbidden territories at the forest limits. 11. T h e problem of reafforestation, raising the biological productivity a n d increasing trees, growth rate o n the forest-limit line as well as the artificial advancement of forest-tundra limits to the north (creation of shelter belts). 12. Botanic-geographical subdivision of the foresttundra territory. 13. T h e elaboration of measures o n the rational use of the forest-tundranatural resources. T h e outlined range of problems is so extensive that it can be achieved only by the combined efforts of m a n y scientists. This calls for the organization of stations for long-term biogeocenological investigations. Most desirable is the organization of a network of stations at the northern forest limits in order to put the study of all the above-mentioned problems o n a strictly experimental basis.

Résumé Importance des limites forestières en tant que frontière biogéographique dans le Nord (B.A. Tikhomirov)

Les limites forestières constituent la frontière biogéographique la plus importante dans le Nord. L’étude de ce problème nécessite un e x a m e n approfondi des caractéristiques de la zone de transition presque circumpolaire entre la taïga septentrionale et la toundra. D e n o m b r e u x spécialistes soviétiques considèrent cette zone (la toundra forestière) c o m m e u n e zone de toundra forestière distincte, qui comprend la zone

38

de la forêt-parc en venant du sud et la zone de la toundra à arbrisseaux en venant du nord. Les facteurs climatiques jouent le rôle le plus important dans le développement de la toundra forestière. Mais il faut tenir compte de la structure et de la composition des c o m m u n a u t é s végétales. L a zone de la toundra forestière doit être divisée e n secteurs selon les arbres qui constituent la limite forestière des territoires. L’étude de ce problème pourra progresser dans l’avenir si l’on entreprend dans des stations des recherches biogéocénologiques de longue haleine.

Forest limits as the most important biogeographical boundary in the North

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Subarctic meteorology 1. M. Dolgin

F r o m the standpoint of making the most efficient use of available natural resources in agricultural development, cattle-breeding and fishery in the subarctic regions,the study of the meteorological régime of this region is of special importance in so far as it affects the activity of animal and plant life as well as the economic activity of man. The Subarctic is a region with a unique nature, the climate of which forms mainly under the influence of the air of the arctic and of temperate latitudes. During recent years and especially in connexion with the realization of a wide complex of research associated with the IGY and IQSY programmes, new data have appeared which w ill be helpful in extending our knowledge of the meteorological régime of the region under consideration. Unfortunately, the microclimate of this region remains nearly unknown. It should be hoped that in realizing the recommendations of the symposium on the ecology of the Subarctic ill be filled up. the existing gap w While preparing this paper w e have come across some difficulties connected with some uncertainty as regards the subarctic boundaries. S o m e definitions of this region m a y be found in references, but they considerably differ from each other. It is true that it must be taken into account that to m a k e such a division into regions is a complicated problem because it can be done only in relation to all the complex of natural conditions which remain to be studied fully. W e have taken the boundaries of the Subarctic as suggested by the academician Grigor’yev (1956) and think that these are the most appropriate (Fig.1). In view of the great longitudinal extension of the Eurasian Subarctic, the underlying surface and circulation conditions and related weather conditions widely differ. Therefore, the meteorological régime is considered in three individual areas: the western area, which includes the territory as far as Taimyr Penin-

sula, the central area covering the territory from Taimyr Peninsula to Kolyma and the eastern area including Chukchi Peninsula and north-easternSiberia.

PECULIARITIES OF THE ATMOSPHERE CIRCULATION The Subarctic is the zone of the most frequent encounters between the arctic air and the air masses of temperate latitudes. That is the reason for the occurrence of the arctic front with different positions in summer and in winter. Using the synoptic data obtained for the last years the front average winter and summer position has been specified in the Arctic and Antarctic Research Institute. In Eurasia its Atlantic European branch approximately coincides with the position determined earlier by Peterson (1961) and Khromov (1948). T h e Asian branch considerably differs. Its summer and winter positions are given in Figure 2. As far as the difference in thermal properties of the continental air of Siberia and of the arctic air is not great in the winter, then the Asian branch of the front in January can be hardly traced. At the arctic front cyclonic activity of varying intensity develops. It is with the Atlantic European sector that the occurrence and active development of cyclones is associated, and within the Asian sector the regeneration of the polar frontal cyclones in the subarctic region (Chukanin,1965) occurs more frequently. In the western area the more frequent recurrence, from four to five per month, of cyclones is typical of the cold period of the year. Their prevailing direction is towards the western area. Over the central and eastern areas their number decreases to two to three per month. In summer over the western area there are three to four per month, but the intensity and velocity of their movements is considerably less than in winter.

41

I. M. Dolgin

Arctic deserts ond siaciers

0

D A r c t i ct u n d r a s Typical ( m o s s and

lichen)

~ ~ n h ~ ' h i l l o c ktundras

Foot-hills' foresttundras. sparsely w o o d e d

stole O 200 400 600 800 km

FIG.1. Subarctic boundaries.

FIG.2. Average position of frontal zones.

42

Subarctic meteorology

In the central and eastern areas of the Subarctic the number of cyclones somewhat increases (four to five per month). They penetrate into the eastern area primarily from the northern part of the Pacific Ocean and into the central area from the south-west,from the central areas of Yakutiya. In the eastern area the anticyclonic circulation predominates over the whole territory in winter, with as m a n y as three anticyclones with low movement and considerable stability. As a consequence of the high recurrence frequency of cyclonic activity in the Subarctic there occur frequent intrusions of cold air masses into the rear of cyclones (in the region of the Subarctic), sharp changes of temperature and winds, frequent occurrence of lower clouds and precipitation (Ragozin and Chukanin,

1961). Peculiarities of circulation processes over the Subarctic are determined by macrosynoptic processes over the Northern Hemisphere. With the change of the type of a macro process the circulation patterns should change considerably over both areas. Apart from average conditions, some aspects of the atmosphere régime are discussed according to the circulation types. For this purpose w e have used theclassification suggested by the late Professor Vangengeim (1961, see also Girs, 1960a). Taking into account the largest features of the atmosphere circulation, Vangengeim established three forms or types

eastern of circulation over Eurasia: the western (W), meridional (C). Each of the three types is characterized by special conditions of the thermal pressure field,by the distribution and value of temperature contrasts, by the distribution of the surface and high altitude pressure fields, etc. During the W type of circulation waves of small amplitude, moving quickly from west to east, are observed at heights. The shifts of cyclones from the Atlantic Ocean to the east are observed at the surface. During the C and E types of circulation the west to east transfer ceases, because of the development of the high-amplitude stationary waves in the troposphere,the geographical position of which with the E and C types of circulation is nearly reversible. There, where with the C type ill be a stationthere is a ridge,with the E type there w ary trough (Fig.3). D u e to this the regions of positive and negative pressure and temperature anomalies during the W type have a zonal distribution and with the E and C types a meridional one. Studies made by Girs (1960b) have shown the existence of the similar circulation types in the Pacific American sector of the Northern Hemisphere and their relationship with the processes over Eurasia. The relation of circulation conditions over the Pacific Ocean to the considered main circulation forms over Eurasia is of primary importance for the eastern Subarctic.

(E)and

- --- -

FIG. 3. Position of ridges and troughs: -a (W), (E), (Cl. (After Gir~.)

-.

43

I. M . Dolgin

T H E RADIATION CONDITIONS O F T H E SUBARCTIC

TABLE1. Total radiation in the Subarctic at northern (N) and southern (S) boundaries of each area (kcai/ cm2/mo)

Nearly the whole of the Subarctic, except for its easternmost regions, is situated to the north of the Arctic Circle. In the south of the western area of the Subarctic the length of the polar d a y period is about a month, with the sun's m a x i m u m altitude at 400-450 at n o o n in June. In the north, in the central part of the T a i m y r Peninsula, the length of the polar day period increases up to 102 days (late April to midAugust). There the sun's altitude is not higher than 38030'. T h e length of the polar night period is about three months (early N o v e m b e r to early February). A s total radiation (Q)is determined by the length of the d a y time, then in January and December it is near O. In the period of the change of the d a y and night the distribution of Q is mainly of latitudinal character. During the polar d a y from M a y to August, Q is different at the s a m e latitude, due to the irregular distribution of cloudiness. As seen from Figure 4, Q increases to the east with m a x i m u m between h = 150~-170~ E, where cloudiness is usually small. T h e annual variation of Q for all the regions is given in Table 1, and in Figure 5 for the eastern area. T h e increase of Q to the north in M a y and June is due to the increase of diffuse radiation caused by the persistence of s n o w cover. T h e northern part of the western area receives about 70 kcal/cm'/yr, the southern one about 75 kcal/cmZ/yr a n d the eastern one 75 to 80 kcal/cm2/yr (Fig.5). Because of the high frequency

Area

January February March April May June July August September October November December

TOTAL

o.1 0.8 4.7 10.0 13.5 13.4 11.9 7.4 3.6 1.3 0.3 0.0

67.0 78.4

0.0 0.3 3.4 9.7 15.5 15.2 12.6 7.6 2.8 0.7 0.0 0.0

0.0 0.7 4.5 10.4 14.8 14.8 13.0 7.9 3.6 1.2 0.1 0.0

--

67.8 71.0

0.1 1.3 5.6 11.0 14.6 14.9 12.0 8.4 4.1 1.8 0.4 0.0

0.7 2.2 7.1 11.5 14.3 14.5 11.7 8.8 5.0 2.9 1.0 0.3

- -

74.2 80.0

of cloudiness and its relatively small vertical thickness a n d due to a long persistence of s n o w cover diffuse radiation amounts to over. 50 per cent of total radiation. In spite of the northern position of the subarctic region the income of total radiation for spring and s u m m e r is rather high. In M a y a n d J u n e it exceeds the monthly values at m o r e southern latitudes.

FIG.4. Total radiation (Kcal/cm2/mo),July.

44

0.1 1.2 5.4 11.4 14.1 14.6 15.5 9.7 3.7 1.8 0.8 0.1

Subarctic meteorology

.I -1 . \ ' 3"'.-.-. ././ ---:y\ -2. ./-./---

Western area of the Subarctic Eastern area of the Subarctic Leningrad Vladivostok

radiation is about O, then in s u m m e r it amounts to 9-10kcal/cm2/mo (Table 3, Fig. 7).

May

June

13.8 14.5 11.6 13.2

14.0 14.7 13.3 11.6

F o r the subarctic ecology the absorbed radiation, determined by the reflective power (albedo) of the underlyingsurface is of primary importance. During the persistence of s n o w cover (7-8months) the albedo of tundra is 85-75 per cent. In June a n d September the value of albedo from year to year can sharply change depending u p o n the dates of the disappearance and appearance of persistent s n o w cover. During the snowless period the albedo of tundra is rather stable: in July and August over the whole of the Subarctic it varies in the range of 9-23 per cent depending o n the character of the underlying surface (Table 2,

Fig. 6). On the

average, for extensive territories, the most important for estimating albedo will be the area of lakes, the degree of tundra wetness and s n o w precipitation.

A n n u a l values of absorbed radiation increase from west to east at the northern boundary of the area from 34 to 38 kcal/cm2/yr, a n d at the southern boundary from 37 to 46 kcal/cm2/yr. Thus, the Subarctic utilizes little of the incoming heat a n d that is one of the m a i n reasons for the severity of the climate of this region. T h e loss of heat by the underlying surface as a result of radiation is, o n the average, about 32 per cent of total radiation for the year. F o r the considered areas of the Subarctic as a result of various combinations of the a m o u n t of cloudiness a n d inversions the annual value of effective radiation differs rather slightly according to regions, e.g., in the west of the area higher frequency of cloudiness a n d lower frequency of inversions than over the central a n d eastern areas are observed. In the north effective radiation ranges from 23 kcal/cmz/yr in the west to 24 kcal/cm2/yr in the east. A t the southern boundary in the east it amounts to 26 kcal/cm2/yr.

45

I. M. Dolgin

FIG. 6. Total radiation (kcal/cmz/year).

FIG.7. Absorbed radiation (kcal/cm2/rno), July. Within the annual variation due to the recurrence of cloudiness, minimum effective radiation is observed in the s u m m e r months. T h e listed components enable us to calculate the radiation balance for the region under study. T h e annual radiation balance for the whole of the S u b arctic is positive a n d amounts at the northern boundaries to 10 kcal/cm2/yr in the west and 14 kcal/cm2/yr

46

in the east. At the southern boundaries from the central to the eastern areas it increases from 12 to 20 kcal/cmz/yr. Table 4 gives the annual variation of the radiation balance (see also Fig. 8). It follows from the table that a positive balance over the whole territory is observed from M a y to September and only in the south-east from April. T h e m a x i m u m balance values occur in July and are 8-9 kcal/cmZ/yr.

Subarctic meteorology

FIG.8. Radiation balance (kcal/cm2/year). TABLE4. Radiation balance of the Subarctic at northern (N) and southern (S) boundaries of each area (kcal/cm2/mo) Area

January February March April May June July August September October November December

-2.0 -1.6 -1.3 -0.1 1.5 6.1 1.7 4.4 1.2 -1.7 -2.2 -2.2 -,

TOTAL

10.4

-2.4 -2.1 -1.7 -0.2 1.2 6.3 8.4 4.5 0.1 -1.9 -2.3 -2.5

7.4

-2.5 -2.1 -2.0 0.0

1.7 8.0 9.3 4.8 0.6 -1.6 -1.7 -2.4 _ j .

12.1

-2.5 -1.8 -1.3 -0.1 2.6 1.5 8.5 5.4 1.4 -1.2 -1.8 -2.2

14.5

-2.5 -1.7 -0.4 1.3 3.9 8.8 1.7 5.4 2.1 -0.5 -1.5 -2.5 ~

20.1

T h e given results o n the radiation régime of the Subarctic are obtained from research data of the Arctic and Antarctic Research Institute (Chernigovskiy and Marshunova, 1965) a n d the M a i n G e o physical Observatory (Barashkova et al., 1961) in Leningrad. T h e albedo characteristics include materials obtained b y the Flying Meteorological Observatory in the Arctic (Kopter, 1961). Radiation balance, as w e k n o w , determines to a considerable extent the heat budget of the given area. T h e latter is also determined by the turbulent flux a n d evaporation value. T h e annual variation of the

components of the heat balance is s h o w n for the northern and southern boundaries of the western area in Figure 9.As seen from this figure, during the period w h e n the radiation balance is negative the turbulent flow is directed to the underlying surface. On the average for the whole of the Subarctic this is observed from October to March. M a x i m u m values of turbulent heat flow occur during J u n e a n d July ( w h e n radiation balance is the most) a n d amount, as is s h o w n by M. I. B u d y k o (1956),to 1.5-2.5 kcal/cm2/mo,with a slight height change. Only a slight increase of annual values of turbulent heat flow to the south is found: from 3 kcal/cm*/yr in the north, to 5 kcal/cm2/yrin the south. T h e evaporation heat loss is O during the period of negative radiation balance (from October to April). A m a x i m u m value of the evaporation heat loss occurs in July, 3.5 kcal/cm2/moin the north of the area a n d 5.5 kcal/cmz/mo of the southern boundary. These values change with longitude slightly. A n n u a l values of the evaporation heat loss in the north of the area a m o u n t to 8-9 kcal/cmZ/yr a n d in the south to 1315 kcal/cm2/yr. Girs considered the change of radiation conditions of the Arctic and Subarctic in relation to the change of the m a i n forms of the atmosphere circulation. Here is a brief outline of his results. W i t h the W type of circulation as stated above, a weakening of interlatitudinal exchange occurs, the activization of cyclonic activity at temperate latitudes is characteristic. W i t h the W type during the w a r m period of the year, a lowered background of pressure is observed mainly over the western a n d eastern part of the Subarctic.

47

L.M. Dolgin

9.0

FIG.9. Annual variation of heat budget components.

b

8.0 -

7.06.0. 5.0-

4.03.02.0-

1.00-1.0-

2.0'

'

'

,-2.'o.

J F M A M J J A S O N D

-

-. -. -. Radiation b a l a n c e -Evaporation ..-..-----_ Turbulent heat e x c h a n g e

" '

I

'

""

I

(a) Northern b o u n d a r y of the Subarctic (b) S o u t h e r n b o u n d a r y of the Subarctic

This leads to the stability of cloudiness here and, as a consequence, to the decrease of total radiation. T h e central area of the Subarctic is characterized by a positive anomaly of pressure a n d anticyclogenesis contributing to the advection of a greater a m o u n t of direct radiation and, consequently, to the increase of total radiation. W i t h the E a n d C types of circulation the meridional distribution of the areas of pressure a n d temperature anomalies are characteristic. T h e development of a stationary anticyclone over the European continent blocks the west-east m o v e m e n t of cyclones, which is typical of the W - t y p e processes. This leads to the advection of w a r m air into high latitudes. Thus, for example, with the E-type process in the west and east of the Subarctic a n anti-cyclonic régime and negative air temperature anomaly prevail. In these areas with the E type total radiation is considerably greater than with the W type due to the increase of the a m o u n t of direct radiation. During the transformation of the circulation type W - t E , east of Taimyr, total radiation decreases by m o r e than 4 kcal/cm2/mo, and over Chukchi Peninsula increases by 2.7 kcal/cm2/mo. In small areas under the influence of local factors microclimatic features m a y be observed which differ from the climate of the whole region. A s has been shown, depending u p o n the nature of soil a n d plant cover within the territory of the s a m e region, different values of albedo are obtained. Elements of radiation balance in the s a m e region with different relief m a y change even more. Let us give s o m e characteristics of total radiation for slopes which depend, first of all, u p o n their steepness. T h e greatest difference exists between their northern and southern sides and this is especially true of the region under consideration. W i t h the persistence of a well-defined diurnal variation absolute values of

48

'

J F M A M J J A S O N D

total radiation vary only depending o n the situation and steepness of a slope. T h e y change depending o n the angle of incidence of solar rays o n the slope. Table 5 gives diurnal totals of solar radiation for northern and southern slopes with different inclination. For southern slopes these values increase and for northern ones they decrease with steepness (Zakharova, 1959).

TABLE5. Diurnal totals of solar radiation for northern and southern slopes ('p

= 700) in kcal/cma Percentages

Inclination

+ 230

Northern slopes 400 300 200 1O0 Horizontal surface Southern slopes

460 544 599 636 663 681 703 714 706

1O0 2O0 3O0 400

00

+ 230

00

O

8 79 157

52 80 90 96 100

O 5 50 100

225 293 346 400

103 106 108 107

143 187 220 255

O

O

According to changes in totals of heat obtained the differences in exposure of slopes m a y greatly overlap in the geographic latitude. If one compares the diurnal totals of solar radiation at the horizontal surface at a latitude of 420 with the diurnal totals of Q at southern slopes at a latitudes of 700, then with the gun's declination being + 230 and + 130,steep southern slopes, in spite of a latitudinal difference of 280, almost fully componsate for this difference (Table 6).

Subarctic meteorology

TABLE6. Diurnal totals of solar radiation at southern slopes

= 700 as a

percentage of the totals at the horizontal surface at rp = 42O at rp

Declination of B u n

.

+23O +13O

O0

-130 -230

Indination of southern slopes

100

200

300

400

92 76 50 16

95 86 64 26

O

O

96 92 76 40 O

95 96 88 47 O

In June with the sun’s altitude of 400-460at noon the slopes facing the sun and having an inclination of 450-500receive from the sun 4-5 times more heat than that received by the horizontalsurface, additional heat received by southern slopes provides for a short period of vegetation of agricultural plants. Western and eastern slopes receive as m u c h heat as the horizontal surface.

SOME METEOROLOGICAL FEATURES OF THE SUBARCTIC WIND

REGIME

In winter a considerable negative radiation balance contributes to a severe cooling of the earth surface and lower atmosphere, but intense cyclonic activity often sharply breaks the severity of the winter régime directly influencing the meteorological conditions of the western and eastern areas of the Subarctic. As a result mean pressure fields over them have low values and high pressure gradients. The western area is covered by the southern part of the Icelandic Trough directed to the north-eastinto the arctic seas and the eastern area is covered by one of the troughs of the Aleutian L o w directed to the Chukchi Sea. The cyclonic activity, which is especially, intense in the west, determines a great variety ofmain meteorological elements. The m a x i m u m variability of mean monthly pressure, in winter particularly, is observed in the northern part of western Siberia and is equal to k6-8mb.A large extension of the Asian High has a direct influence upon climatic peculiarities of the central area of the Subarctic. This position of pressure fields determines essential differences in the wind régime of the Subarctic (Prik,1964~). In winter over the western area of the Subarctic, south-westerly and southarly winds of considerable velocities are observed. Over the northern coast of the Kola Peninsula and over the Y a m a l and Gydanskiy peninsulas average velocities are 7-9m/s.Winds with a velocity of 6-7 m/s are mostly observed (20-25per cent) and for 5-10days in a month there are storms.

Over the central area and the western part of the eastern area and due to prevalence of the anticyclonic weather with low pressure gradients, south westerly winds also predominate, veering into westerly winds but with low velocities (1-3 m/s),and calm periods often occur. Storms are rare in winter, on the average, as m a n y as 3-5times in 10 years. Only in the easternmost areas over Chukchi Peninsula, and more to the south does an air flow directed from the north-east with high wind velocities (6-8m/s) prevail. T h e number of storms increases. On the average 5-8 days with storms are numbered in a month. Orographic conditions of the country have a signscant influence on the direction and velocity of wind. A distortion of the direction of the air flow, greater or, on the contrary, lesser velocities often occur. In the valleys of the rivers Ob’, Yenisey, Khatanga, Kolyma, etc., or in narrow bays-for instance in Ob’ Inlet and Khatanga Bay- the direction of the prevailing air flow is distorted and the flow runs in the direction of the river valleys and bays. In summer, as a result of the development of the cyclonic recurrence, which is especially intense over the north of eastern Siberia, the mean pressure field is characterized by an extensive but shallow depression over Siberia and increased pressure at higher latitudes, which determines the prevalence of winds with, primarily, the northern components of north-easterly ones. Only in the extreme east of the Subarctic do they transfer into south-easterlyand southerly winds. Thus, winds opposite to winter ones (i.e. of the type of the summer monsoon) predominate there. Slight pressure gradients in summer determine a lesser recurrence of prevailing directions than in winter. Only under the influence of orographic conditions, as happens in winter, is the direction of local winds more stable, especially if this wind coincides with the wind associated with the pressure field. In the river valleys, as in other seasons, winds prevail along the valleys, but in summer their direction is opposite to that of winter. For example,if in the valley of Yenisey the southern wind prevails in winter, then the northern wind prevails in summer. Wind velocities in the western and eastern areas of the Subarctic decrease considerably,and the number of days with storms over the month is reduced (1 or 2). In north-eastern Siberia, due to the cyclogenesis in summer, wind velocities on the contrary increase and reach a m a x i m u m in the annual variation, but still they do not exceed, on the average, 4.5-5.5m/s, and days with storms run to 1-2in a month. Only under the influence of orographic conditions m a y wind velocities considerably increase in some places. The relation of wind régime to ecology is of primary importance. With a weakening of the wind, the cooling of a plant tissue decreases and,if the wind is intended the cooling increases. With increased wind velocity, evaporation on the slopes increases and these are in a

49 4

I. M. Dolgin

worse condition of wetting as compared to the flat country. Therefore it is necessary to take into account the wind distortions due to the relief of the country. It is k n o w n that with winds blowing along a valley one can observe their intensification over the bottom of the valley and with winds directed across the valley s o m e decrease invelocity is possible. W i n d s are stronger at the tops ofhills, and weaker behind a n obstacle. T h e m e c h a nical influence of the relief u p o n wind depends o n the atmosphere stability. U n d e r stable conditions over elevations the increase of wind velocities is m o r e than that found under unstable ones. Therefore, at the top the wind velocity conditions under stable air m a y be twice as high as that at the foot of a slope. U n d e r unstable stratification wind velocity at the top m a y be approximately 1 m/shigher than that at the foot. Air flow in the dissected country has also a thermal influence contributing to the occurrence of local circulation. D u e to the non-homogeneous cooling over a slope and the adjacent atmosphere layers, slope winds occur, resulting in the accumulation of cold air at the foot of the slope and a temperature difference of about 100 C m a y appear between the top and foot. No special studies have been carried out o n the influence of exposure and topographic forms u p o n meteorological conditions in the Subarctic. However, s o m e quantitative characteristics obtained for t e m perate latitudes by the M a i n Geophysical Observatory of the U.S.S.R. m a y be applied to the subarctic regions. These are the coefficients of wind velocity variations in relation to topographic forms in a hilly country as compared to a flat country obtained Ky Gol’tsberg (1961) (Table 7) from extensive experimental data and special literature.

TEMPERATURE

REGIME

T h e Subarctic is characterized by rigorous long winters a n d short cool summers. T h e air temperature of the coldest m o n t h s is nearly the same. According to m e a n multi-annual data the January m i n i m u m is slightly pronounced. S u c h a temperature variation is accounted for b y heat advection in mid-winter in s o m e years; as a result, the m e a n temperature of one of the winter months appears to be higher than that of the adjacent months (a w a r m core) (Dolgin, 1964). Thus, for example, in Salekhard in 1960 the temperature in February appeared to be w a r m e r than that in January and M a r c h by Il0 C. In K y u s y u r in 1933 January w a s w a r m e r than December by 120 C a n d w a r m e r than February by 40 C. A s Rubinshstein (1962)has s h o w n this p h e n o m e n a is observed in the whole of the Subarctic. In its western area the frequency of the w a r m cores amounts to 35-45 per cent, in the central area it decreases to 10 per cent and in the extreme east it increases u p to 50-60per cent. T h e diurnal temperature variation in winter is negligible, its amplitude is 0.20-0.30 C. It is irregular a n d sometimes the temperature reverses w h e n maxim u m falls o n night hours and m i n i m u m o n d a y hours (Rubinshtein, 1958). T h e temperature field in winter in the Subarctic is non-homogeneous (Fig.10). T h e western area is the warmest one affected by Atlantic cyclones and by one of the branches of the Gulf Stream. Thus, at the northern coast of Kola Peninsula the m e a n January temperature amounts to -60 C, -80 C, southward it drops to -120 C, -140 C. Eastward the air temperature also decreases reaching -240 C, -260 C in the west Siberian part of the Subarctic. In the central

TABLE7. Coe5cients of wind velocity variations in a hilly country in relation to topographic forms (for wind velocities from 2 to 7-8 m/s)as compared to an exposed flat country Coefficients with winds blowing towards the axis of a ridge or a valley Topographic forma

in parallels

perpendicularly

at an angle of 450

Exposed flat country Tops of exposed elevations (Ah > 50 m , slope > 100). The upper one-third of windward slopes of the same elevations Tops of small gentle elevations (Ah < 50 m , slope i 100). The upper one-third of the same elevations Middle parts of windward slopes (exposed) Windward slopes of small elevations facing valleys Leeward slopes of elevations.(Ah > 50 m , slope > 100)

1.0

1.0

1.0

1.3-1.4

1.4-1.5

1.4-1.5

Leeward slopes of elevations (Ah < 50 m, slope < 100) Bottoms of valleys, hollows, ravines exposed to winds if wind blows up the valley Bottom of valleys, hollows, parallel to wind if wind blows from below up the valley Bottom of small closed depressions

50

1.0-1.1 1.0-1.1

1.1-1.2 1.1-1.2 1.0-1.1 1.0-1.1 0.9-1.9 0.9-1.0 F r o m 0.9-1.0 in the upper part to 0.6 in the lower part of the slope 0.6-0.7 0.6-0.7

__

1.o-1.2

0.4-0.5

0.6-0.7

-

0.7-0.8

__

Subarctic meteorology

FIG. 10. Mean air temperature,January. area under the influence of anticyclonic circulation temperature drops to -360 C, -400 C. In the easternmost part affected by Pacific cyclones the mean.temperature quickly increases reaching -270 C, -280 C in the far east tundra a n d -200 C or -220 C near the Bering Strait (Girs, 19606; Shcherbakova, 1961). Frequent changes of pressure systems, especially in the western and eastern areas of the Subarctic, produce large periodic temperature variations. Interdiurnal variability in the west is, on the average, 50-60 C, its m a x i m u m values reach 200-250 C. Extreme temperature values in winter a m o u n t to -270 C, -330 C and +50 C, -70 C at the coast of Kola Peninsula; between the lower course of the Ob' and Yenisey rivers they a m o u n t to -450 C, -500 C and -20 C, -30 C, and at the coast of the Bering Sea -350 C, -450 C a n d +30 C, $50 C. T h e largest amplitudes in the winter observed in the central area range from -500 C, -600 C to +20 C, -40 C. T h e given minimum temperature m a y considerably change depending o n the nature of relief.

Mishchenko (1962) obtained corrections to the average from absolute annual m i n i m a of the air tempefor the Subarctic, where three areas rature (Tmin) with different corrections are selected; they are given in Table 8. In s u m m e r a continuous flux of solar radiation contributes to the quick w a r m i n g of the tundra surface. T h e surface layer of the ground in July in the south of the subarctic gets w a r m e d up to 140-160C, and near the coasts of seas a n d on T a i m y r Peninsula UP to 70-8"C. T h e active surface temperatures QN are good evidence of a m o r e complete estimation of daytime heat resources. A t the M a i n Geophyeical Observatory, QN are calculated for the day o n the basis of the use of the heat budget m e t h o d not only for a flat country, but also for the northern and southern slopes. It is k n o w n that vegetation behaves differently on slopes with different exposure. T h e differences in the duration of plant development phases m a y b e from 5 to 18 days o n the northern a n d southern slopes,

TABLE8. Tminchanges under the influences of relief as compared to a flat country (in 0C)I Arei characteristics

Levelled areas with poor relief (Ah = 20-50 m) Hilly relief (Ah = 50-150 m) Low and middle mountainous relief (Ah = 150-300m) 1.

Broad valley

TOP

-2 -3, -4,

-4 -5

1.5 +2, 3

Narrow vaiieyhollow

+39

$3

+49

+5,

+4 +5 +6

Top-hollow .

5-6 7-9 9-11

(-) and (+)designate Tmi, increase and Tmindecrease respectively, in comparison with an exponed flat country.

51

I. M . Dolgin

respectively. Therefore, accomplished calculations enable us to m a k e a m o r e correct approach to the economic estimation of the differences in thermal régime which appear o n slopes with different exposures. Calculation data obtained for Khibin, Verkhoyansk and Turukhansk are given as a n example in Table 9 (see Mishchenko, 1965). T h e transfer to the prevailing positive air temperatures takes place from early M a y at Kola Peninsula to late June in the north of T a i m y r Peninsula. T h e warmest m o n t h everywhere is July (Fig. 11) being w a r m e r than June by 60-70 C a n d w a r m e r than August by 20-40 C. In the north this difference decreases. T h e field temperature in s u m m e r throughout the whole of the Subarctic is m o r e homogeneous than in winter. T h e highest temperature of 130-140 C is characteristic of the southern part of the western S u b arctic and its easternmost part. A sharp temperature fall of 40-60 C in July occurs near the shores of cold seas, the horizontal temperature gradient here is considerable and, in places, amounts to 6-100/100km.

TABLE9. Differences in thermal régime calculated of three stations (these corrections m a y also be considered tentative values for the Subarctic) QN variations at daytime in comparison with the horiaontal surface Southern slope

Station

Month

100

ZOO

100

200

Khibiny

May June July Aug. Sept.

-1.5 -0.8 -0.8 -1.4 -1.4

-2.6 -1.6 -1.5 -2.6 -2.6

2.2 1.0 1.4 2.4 2.2

1.1 0.6 0.9 1.1 1.2

Verkhoyansk

May June July Aug. Sept.

-1.1 -1.1 -1.1 -1.8 -2.3

-2.2 -1.7 -2.2 -3.6 -3.1

1.8 1.5 2.1 3.2 2.5

1.0 0.7 0.7 1.4 1.4

Turukhansk

May June July Aug. Sept.

-1.4 -1.1 -1.1 -1.6 -2.0

-1.9 -1.7 -2.1 -3.3 -3.1

1.6 1.5 1.8 3.2 2.2

0.7 0.8 0.7 1.7 1.2

A s a n example, m e a n multi-annual air temperatures for the stations situated at different distances from the sea over the western area are given below: January

52

TABLE10. Changes of At depending on location in comparison with an exposed flat country (in OC)' Corrections to Location

M e a n multi-annual

Tops and upper parts of slopes Bottom of brood valleys (more than 1 k m across) Closed valleys or hollows Banks of lakes and large rivers 1.

(-) and (+)are the with a tlat country.

A, (MayAugust)

-10

-1.50

+1 -2 1.5 -2.5 +1 -2

With clear skies

-20

-30

-2 -3

-4 -5 -4

+2

At decrease and increase respectively. in comparison

T h e change of At has a n essential influence on the plant growth (Mishchenko, 1965). These corrections are given for temperate latitudes. For the Subarctic these will be s o m e w h a t less because the diurnal temperature amplitudes are less there. T h e diminution of circulation intensity in s u m m e r leads to a decrease of interdiurnal temperature change, its m e a n value being only 10-30C a n d m a x i m u m value

100-150 C.

Northern slope

Lower Pesha, Vzglav'ye Lower Pesha, village Murmansk Kola

T h e amplitude of the diurnal temperature variation a n d it is very sensible to microrelief (Table 10).

(At)is 40-50 C

-14.4 -14.8 -10.0 -11.3

July

11.6 12.5 12.9 12.9

Extreme temperature variations are notable in July w h e n the absolute m a x i m u m everywhere is 300-320 C, except for T a i m y r Peninsula. Absolute m a x i m u m will drop to between-lo C and 30 C, but in the southern part of the Subarctic negative temperatures are very seldom observed (Prik, 1964b). A stable frost-free period ( w h e n frosts are absent for at least a month) m a y not be distinguished in all areas. T h e last frost is observed in the southern areas of the western Subarctic, o n the average, at the end of the second ten days, and in the eastern Subarctic in the third ten days of June. A t T a i m y r Peninsula a n d near the coasts of eastern arctic seas light frosts of -lo C m a y occur even in July, ground frosts disappearing one or t w o weeks later. T h e first frost in the northern areas is observed in mid-August, in the southern areas in the northern part of Arkhangelskiy region in early September, and o n the northern coast of Kola Peninsula in late September. A s a result, a frost-free period (Fig.12) of about a m o n t h is observed near the arctic seas and at T a i m y r Peninsula, but it rapidly lengthens with greater distance from the sea. Its longest duration of 3 to 3.5 m o n t h s is observed in the north-west of the Arkhangelskiy region and o n the northern coast of Kola Peninsula. Local relief has an essential influence u p o n the duration of the frost-free period. In the area of Y u g o r a n d T a i m y r peninsulas (excluding the areas of highest

Subarctic meteorology

FIG.11. Mean air temperature, July.

FIG.12. Duration of frost-free period.

elevations) with elevations of about 300 m at the concave topographic forms, the frost-free period decreases by 20 days and, at the convex topographic forms, it increases by 20 days in comparison with its period in a flat country. In the northern part of W e s t Siberian Lowland, with a n average length of the

frost-free period of 60-90 days o n hills 100-150 m height, the frost-free period decreases o n the average by 15 days, and in the Yenisey valley under the influence of the w a r m waters transported from the south this period increases by 15 days. In the central area between the Anabar and Olenek

53

I. M. Dolgin

rivers, in the valleys of Pronchishchev Ridge, the frost-freeperiod is reduced by 20-25days, and on the tops and upper parts of slopes it increases by 20 days. On the knolls (of 150-300 m height) lying south of Tiksi Bay, the length of the frost-free period ranges from 45 days in valleys to 80 days on hills (Anon.,

1962). Depending on relief frost intensity also changes. If, as was mentioned above, minimum temperatures in summer in the southern areas of the Subarctic reached -lo C, -30 C in a flat country, then over a rough country these temperatures m a y essentially vary. On hill tops minimum temperaturewill be higher by 20 C and in valleys lower by 1.50-40C than in a flat country.These values depend on weather conditions. In individual years summer frosts as a result of advection of cold air masses from the north are possible throughout the whole of the Subarctic. In the northern areas the frost-free period is practically absent. On the ground the frost-freeperiod is shorter by 0.51.5 months than in the air. T h e earliest autumn transit of air temperature over O0 C occurs in the north of Taimyr Peninsula during the first ten days of September and the latest one is observed on the coast of Kola Peninsula during the second ten days of October. Thus, the period of prevailing positive diurnal temperature lasts for 5060 days in the north of Taimyr Peninsula and increases to 160 days at Kola Peninsula. The total of positive temperatures for this period in the north of the subArctic is 100~-200~ C,in the south of the western area it rises up to 800~-1,000~ C, and westward from the

Urals up to 1,2000 C (Fig.13). The totals of temperatures for the period with a steady temperature of over $50 C,even in the south of the western and far C; in eastern Subarctic, do not exceed 800~-1,000~ the northern part of the western and eastern areas C. of the Subarctic these drop to 100~-200~ O n e of the most characteristicfeatures of the thermal régime of the Subarctic is the existence of temperature inversions, both surface and upper throughout most of the year. The inversions, to a considerable extent, determine the nature of the Earth’s surface radiation,cloudiness and precipitation. It is k n o w that the upper boundary of the surface inversion coincides with the lower boundary of the lower clouds, that steady fogs are associated with the inversion, etc. The most frequent recurrence of the surface inversions throughout the whole of the Subarctic falls in February and March. Over the western area days with inversions amount to 40-60per cent of the period, over the central and eastern areas to 60-90 per cent. By July the recurrence of the surface inversions diminished to 10-20per cent. The thickness of the inversion k m ,in the central layer over the western area is 0.6-0.8 and eastern areas it is 0.8-1.1 km; in summer, it is 0.4-0.6 k m everywhere. The intensity of inversions in winter is 30-60 and 70-130 respectively, and in summer it is 20-40 throughout the Subarctic. As a result of such a stratification of the atmosphere the difference of mean monthly air temperatures (according to multiannual data) of the stations Yukskor (altitude 902 m) and Appatite Mountain (altitude

FIG.13. Totals of air temperature for the period of stable temperature above O0 C.

54

Subarctic meteorology

360 m) in January is only -0.80 C and in July, when the inversion frequency is negligible it is -3.70 C (Anon, 1965). The temperature differences of the Appatite Mountain station and Khibiny station (altitude 134 m) in January amount to $1.30 C, and in July -1.00 C (Anon., 1965). In the central and eastern areas, in winter at a height of 1 k m , temperature m a y be higher than at the surface by 9-100 C. In the snow melting period and in summer, inversions begin from the height of 200-300m. Such inversions are rather frequent but of lesser intensity and thickness. Surface inversions of long duration have an unhealthy influence on the organism of m a n and animals because reduced air mixing results in an accumulation of aerosols and CO in the lowest layer of the atmosphere. WETTING

REGIME

Precipitation

The most intense cyclonic activity in the western and eastern areas of the Subarctic is associated with a greater amount of precipitation occurring in those areas. At Kola Peninsula and in the southern part of the western area, as well as in the extreme east, over 350-400 m m of precipitation occurs in the course of a year (Fig.14). Under the influence of relief, the amount of precipitation m a y rise in s o m e places up to 500-600mm. The least amount of precipitation, i.e. 150-200 mm, falls on the central area where in winter anticyclonic activity predominates. In the annual trend the least amount of precipitation, within almost all of the territory under consideration, occurs in February and March: in the west and east 15-20 mm, in the central area 7-10m m in a month (Prik, 1965). M a x i m u m precipitation occurs at the end of summer, in August and September (Fig. 15). The greatest amount of precipitation occurs at this time in the western area, in the south as much as 45-50 m m in a month, but in the north the amount decreases to 30 m m in a month. In the central area the amount of precipitation is less: 40 m m in the south and 25 m m at the northern boundary of the area. The increase of precipitation is observed in the eastern area, in the north it amounts to 30-35m m monthly, and in the Far East, as a result of advection of wet sea-air masses from the Pacific Ocean, the quantity of precipitation exceeds 50 mm. Precipitation in the whole of the Subarctic during summer months is frequent: from 13 to 15 days in a month. This is a period with mainly drizzling rain and occasional wet snow in the northern areas. The number of days with precipitation of no less than 2 m m per day does not exceed one-third of the total

number of days with precipitation but sometimes the daily amount m a y reach 25-40mm. The Subarctic is typical of an exclusively long period of persisting snow cover. In the extreme west it is about 200 days, in the eastern part of the western area as well as in the central and eastern areas this period increases to 230-250 days. The snow cover, settling for the entire winter, appears in the northern part of Taimyr Peninsula and in the north of eastern Siberia in late September, and in the W e s t Siberian tundra in the first ten days of October (Fig.16). Later still, in early November, the snow cover settles in the extreme western and eastern areas affected by w a r m air and water masses. The lapse of time from the appearance of the first unstable snow cover to its settling for the whole winter is from 10 to 12 days in the central area and from 20 to 30 days in the western and eastern areas. The earliest disappearance of the snow cover occurs at Kola Peninsula at the beginning of the second ten days of May, and in the north of Arkhangelskiy region in the third ten days of M a y (Fig. 17). In western Siberia the disappearance of the snow cover occurs from the first ten days of June in the south of the area to the third ten days of June in the North Taimyr Peninsula, and in eastern Siberia primarily in the first ten days of June. Only in the lower course of the rivers Indigirka, Kolyma and in the valley of the Anadyr does the snow cover melt in late May. The height of the snow cover before melting in the western area is 60-70cm, in the central area 30-40cm and in the east up to 50-60 cm. The snow cover is very irregular, especially in sites where strong winds prevail. Snow is blown away from exposed and particularly elevated sites but accumulates in sites of low relief where it remains throughout the summer season. Very low values of absolute humidity, as a result of low temperatures in winter, are especially characteristic of the Subarctic. The hoar-frost and rime formation due to radiation cooling over snow contribute to the decrease of humidity content. Only on the coast of Kola Peninsula does the mean monthly value of absolute humidity amount to 3.5 mb, while moving to the east it decreases to 0.3-0.5 m b in the central area, but in the extreme east it increases again to 1.5-2 mb. The surface temperature inversions produce a slight increase of absolute humidity with height in the lower atmosphere. In summer absolute humidity rises and in the southern area of the Subarctic it amounts to 11-12 mb and in the northern area 7-8mb. The relative humidity in winter is about 85 per cent in the west and 75 per cent in the central area; in the east it rises slightly. W h e n temperature is very low, the air is often oversaturated with water vapour, but there is neither condensation nor sublimation because of an exceptional purity of the air and the lack of condensation

55

I. M. Dolgin

FIG.14. Amount of precipitation (rnmlyear).

FIG.15. Monthly amount of precipitation (mm), August. nuclei. W h e n the condensation nuclei are inserted into the air, freezing fog and cloudiness appear. During this season of the year in the lower 1-kmlayer relative humidity varies little with height. In summer, in the southern area of the Subarctic, relative humidity is 75-78per cent, in the northern area it increases to

56

80-85 per cent. With height the relative humidity decreases. The diurnal variations of relative humidity in the northern area is very slight in summer, the diurnal amplitude is 4-6per cent. In the southern part of the western Subarctic it rises to 12-16 per cent, and in

Subarctic meteorology

FIG.16. Average dates of the formation of persistent snow cover.

FIG.17. Average dates of destruction of persistent snow cover.

the southern part of the central area it becomes still higher. Humidity as low as 30 per cent and less occurs very seldom and only during the advection of w a r m air from the south in some places where the w a r m air moves over elevations lying close to some areas of the

Subarctic (foehns), reducing relative humidity sometimes to 23-25 per cent. This is observed at Kola and Taimyr peninsulas, near the Lena Delta and in northeastern Siberia. At the foot of slopes and in valleys, due to temperature decrease at night-time,relative humidity essen-

57

I.M. Dolgin

tially increases resulting in more frequent formations of fog and dew. With the increase of wind velocities, heavy cloud cover and high humidity, the differences in humidity depending on reliefform smooth down. Owing to frequent non-intensiveprecipitation,high relative humidity and low air temperature, the evaporation process in the Subarctic proceeds slowly and the evaporation is slight. In the northern part of the central area less than 50 mm of moisture evaporates over the course of a year; to the west, east and south evaporation increases and in the southern part of the western Subarctic reaches its highest value of 150-200 mm. Thus, in the Subarctic, precipitation exceeds evaporation resulting in surplus wetting of grounds. The most intense evaporation is observed in July when 20-30 per cent of the annual total evaporates. It is necessary to take into account the macro- and microclimatological conditions given above for the distribution of agricultural plants within individual forms. According to studies made by Gol'tsberg, agriculture is possible in the Subarctic only in hot-houses. The long days of the polar summer favour plant growth in hot-houses with heating of different kinds, which should be arranged,if possible,in sites protected from northern winds. If the site is hilly, it is recommended that the hot-houses be installed in the middle of the southern slopes. As already mentioned, in some areas of the Subarctic the length of the frost-freeperiod in the air is from 60 to 90 days, and on the surface of the ground and vegetation cover from 30 to 60 days. Agriculture in these areas is possible primarily on slopes and in broad valleys with a well-drainedsoil and on the banks of large rivers and lakes where the frost-free period increases by 15-20 days and soil is not overwet. The bottom of broad deep valleys is very dangerous in respect of frost. It is recommended to use natural or to create artificial protections from northern winds. In the area of permafrost, when the moss cover is removed, the soil drained and ploughed, the ground receives more heat and the layer of soil melting during the summer gradually increases. For faster and better warming of the soil in the north a ridge-like surface of the fields is recommended. It should be indicated that for the solving of a number of problems related to the ecology of the Subarctic a more thorough study of this region is necessary, in a number of cases one can make only shortterm itinerary microclimatologic observations which will characterize, first of all, the distribution of minim u m temperatures and wind velocities (Anon., 1960; Gol'tsberg, 1961).

considerable changes. When studying them scientists, for several reasons, often limit themselves to studies of air-temperaturevariations which can sharply affect the development of plant and animal life. A detailed analysis of temperaturevariations is given by Rubinshtein (1956)and Polozova and Rubinshtein (1963).On the basis of sliding 10-year mean monthly temperatures the author has shown that regular m a x i m u m temperature variations are observed to the north of 400 N. and more distinctly pronounced during the cold period of the year. Thus, for instance, in Salekhard in January the air temperature for the period 1944-53 appeared to be higher by 90 C than that of 1885-94.In Anadyr the air temperature for the period 1945-54was higher by 60 C than that of 1931-40.In summer the variations of 10-year means are a little less but the amplitude still exceeds 30 C. The curves of sliding temperatures constructed by Rubinshtein show that the temperature changes have periods of over 10 and 35 years (Fig.18).The horizontal line in the graph shown mean multi-annual temperatures reduced to the period 1881-1960. The curves of Upernivik and Salekhard are examples of temperature variations for 35 years: at the latter station the temperature in January was 220 C for the period of 1891-1925, and -170 C for the period

1924-58. In the latitudinalzone of 600-700N.the synchronous variation of 10-year mean temperatures from Torgshavn to Salekhard and a nearly inverse temperature variation at the Chukchi Peninsula and Alaska are observed. The amplitude of variations in the western area of the Subarctic is miich greater than that in the central and eastern areas;this is due to the fact that the temperaturevariation is more distinctly pronounced in the areas of intense cyclonic activity. In our opinion a comparison between the temperatures for the periods

Climatic changes T h e climatic conditions of any region are subject to

58

FIG.18. Sliding 10-year mean monthly air temperatures.

Subarctic meteorology

1941-60 and 1921-40 (Rubinshtein, 1956) are of unquestionable interest (Table 11). TABLE11. Mean temperature differences in

OC

for the

periods 1941-60and 1921-40 Stations

Time

Dikson

Salekhard

Turukhsnsk

K?z:kuly

April May June July August September Year

2.7 0.8 0.3 o.1 -0.1

o.o 0.3

1.2 0.6 0.8 0.3 0.7 -0.2 -0.2

2.1 2.1 0.6 0.0 0.2 -0.2 0.1

2.2 1.6 1.3 0.9 -0.2 0.2 0.2

Table 11 gives temperature variations only from April to September. In winter an inverse relation is observed for this period, that is, cooling began. In s u m m e r warming u p continued and this affected even m e a n yearly values. As indicated by Rubinshtein the change of m e a n temperature by 0.50-10C already has practical significance. Uspenskiy has reported that o n the territory of Eurasia lying to the north of the forest tundra, due to climatic variations of the last 40-50 years n o less than forty species of birds and m a m m a l s have appeared or considerably increased in population. The extent by which these species m o v e d into the heart of the tundra is estimated by the author to be 0.5010 N. in comparison with the beginning of the century. In Yamal, where the degree of warming w a s highest, this m o v e m e n t amounts to 20 N. Moose which were practically non-existent to the north of the forest tundra in the 1920s have n o w become accustomed to the tundra, and inhabit it u p to the coast of the northern seas. At present it is established that the periods of temperature variations are not strict because of

changes in the nature of the atmosphere circulation associated with changes in solar activity (Dzerdzeevskiy, 1956; Girs, 19606). Vangengeim and Girs have s h o w n the existence of the epochs of the forms of circulation when an a n o m a lous development of the processes of one type (or two) and weakening of the processes of the other types h a d taken place for a long time. Thus, for instance from 1900 to 1928 there existed a n abnormal development of the processes of the W-circulation type producing over the area under consideration, except for the western and eastern peripheries, positive temperature anomalies with the highest values over western Siberia. F r o m 1929 to 1931 there existed the epoch of the E-circulationtype and a positive temperature anomaly covered the entire Subarctic at that time. The highest values of anomaly fell o n the western and easternareas and that w a s in agreement with the conditions of the given circulation type. This epoch of circulation then w a s replaced by the epoch of the C-circulation type (1940-48) when a positive temperature anomaly w a s observed only in the region adjacent to the K a r a Sea. During recent years (1949-64)an abnormal development w a s taken by the E and C types of circulation over Eurasia with an abnormal development of the .W-circulation type over the Pacific Ocean. Under the influence of the latter there was a rearrangement of the E and C types of circulation into the W type over Eurasia which started in the 1950s. This rearrangement reached the highest intensity by 1964 resulting in, at that time, a greater anomaly of temperature over the western and eastern areas of the Subarctic. Over the central area the temperature anomaly appeared to be negative. T h e probability of positive anomalies increased over the western area by 20 per cent and in the east by 23 per cent. At the present time rearrangement has not yet been completed. Taking into account this situation, a further warming u p should be expected in the next few years and, consequently, a m o v e m e n t farther north of a n u m b e r of animals from these regions should also be expected.

Résumé Météorologie subarctique (I. M. Dolgin) L’étude d u régime météorologique des régions subarctiques présente un intérêt particulier si l’on veut tirer tout le parti possible des ressources de ces régions pour le développement de l’agriculture, de l’élevage et- de la pêche. Selon l’académicien A. A. Grigoriev, la frontière méridionale de la région subarctique est située à la limite entre la toundra et la taïga.

D a n s une portion longitudinale considérable de la région subarctique, on constate de grandes différences en ce qui concerne les conditions de la circulation atmosphérique et le régime d u rayonnement. C’est pourquoi l’auteur examine le régime météorologique des régions occidentale, centrale et orientale. D’après l’analyse des composantes d u bilan de rayonnement, o n constate que, dans l’ensemble d u territoire considéré, ce bilan a une valeur annuelle positive qui varie selon la latitude de 10 à 14 kcal/cm2

59

I. M. Dolgin

par an. L’auteur examine les composantes du bilan thermique. Se fondant sur la classification de G. Y a . V a n g e n heim et A. A. Guirs, l’auteur indique les variations de rayonnement dues à l’alternance des principales formes de la circulation atmosphérique et démontre que, dans les régions occidentale et orientale, le rayonn e m e n t total est beaucoup plus grand avec les formes E et C de circulation qu’avec la forme W. L’auteur montre les variations du bilan de rayonnem e n t sous l’effet des facteurs locaux. Les variations des quantités globales de chaleur reçue en fonction de l’exposition des pentes peuvent être supérieures a u x différences dues à la latitude géographique. L’auteur donne des renseignements plus précis sur la position du front subarctique e n été et e n hiver, et sur les particularités de la circulation atmosphérique dans les régions subarctiques.

-

Le climat des régions subarctiques est sujet à des fluctuations considérables. L’auteur indique les caractéristiques des variations de température selon Rubinstein et leurs relations avec les formes de circulation d’après A. A. Guirs. En 1960-1965,un accroissement considérable de la température a été constaté dans les parties occidentale et centrale de la région subarctique, ce qui peut avoir pour effet d’attirer davantage d’oiseaux et de mammifères dans les régions septentrionales de la toundra. L e mésorelief et le microrelief ont une influence considérable sur la répartition des températures, d u vent, de l’humidité, des précipitations et de l’enneigement. L’auteur indique certaines caractéristiques microclimatiques de la région subarctique. En analysant le régime de la température et de l’humidité, l’auteur tient compte de la stratification des couches inférieures de l’atmosphère.

Discussion F. E. ECKARDT. Pourriez-vousindiquer le type d’instrument utilisé par vous pour la mesure du rayonnement? Pour quelle raison exprimez-vous le rayonnement en kcal/cma/mois au lieu d’adopter le système MKSA rationnalisé recommandé par l’organisation internationale de standardisation? I. M. DOLGIN. In measuring radiation the standard equipment was used which is in use at all actinometric stations in the U.S.S.R.The description of these instruments is widely known. The measurements were made in kcal/cma/mo since the MKSA system has not yet been accepted by the Hydrometeorological Service of the U.S.S.R.

J. MALAURIE.(1) I don’t believe that the distinction between Arctic and Subarctic is very valid from a geomorphological point of view. I a m afraid that a thorough analysis will determine a fragmentation in too m a n y aspects of this distinction for it to have any real meaning. In the high Arctic (Inglefield land) on the maritime border of a plateau, the

conditions are, if the sea ice is broken to 40 per cent, subarctic, according to climatologicaland geomorphic processes. (2) In Arctic, journal of the Arctic Institute of North America, it is stated, in a rather old issue, that the temperature measurements of the coastal stations of the northwest coast prove a decline of temperature since 1940. H o w does this compare to north-eastern Siberia, in Tchoukotkaoblast or Kamchatka? I. M.DOLGIN. (1) W e can speak of two ways of distinguishing the Arctic and the Subarctic. One is based on the general circulation, distribution of air masses and radiation, the second on the dependency of climate on local conditions. I agree with Professor Malaurie that w e are able to find such small areas, like the coastal belt, where the influence of sea water creates subarctic conditions in the arctic zone. (2) In eastern Siberia there has been a real amelioration (warming up) of climate in the last twenty years. In Alaska there has been a slight cooling according to m y map. The climatic changes in this period, as I said, are not the same in the whole of the Subarctic.

Bibliography / Bibliographie ANON. 1960. Atlas sel’skogo khozyaistva SSSR. Moscow, Glavnoye Upravleniye Geodezii i Kartografii Ministerstva Geologii i okhrany nedr SSSR. . 1962. Mikroklimatologiya kholmistogo relyefa i yego uliyaniye na sel’skokhozyaistvennyye kul’tury. Leningrad, Gidrometeoizdat. . 1965. Spravochnik PO klimatu SSSR. Vyp. I, chast’ II, Temperatura uozdukha i pochvy. Leningrad, Gidrometeoizdat. BARASHKOVA, Ye. P.;GAYEVSKIY, V. L.;D’YACHENKO, L.N.

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-_

60

1961. Radiatsionniy rezhim terriiorii SSSR. Leningrad, Gidrometeoizdat. BUDYKO, M . I. 1956. Teplovoy balans zemnoy pouerkhnosti. Gidrometeoizdat. CHERNIGOVSKIY, N . I.; MARSHUNOVA, M . S. 1965. Klimat Sovietskoy Arktiki (radiatsionniy rezhim). Leningrad, Gidrometeoizdat. CHUKANIN, K . I. 1965. Nekotoryye sinoptiko-klimaticheskiye kharakteristiki Arktiki. (Trudy AANII, tom 273.) DZERDZEEVSKIY, B. L. 1956. Problemy kolebaniy obshchey

Subarctic meteorology

tsirkulyatsiiatmosfery i klimata.D.I. Voyeikov i sovremennyye pro blemy klimatologii. Leningrad, Gidrometeoizdat. DOLGIN, I. M . 1964. Bezyadernyye zimy v Arktike. (Trudy AANII, t o m 266.) GIRS, A . A. 1960a. Tipovaya kharakteristika osnovnykh raznovidnostey form atmosfernoy tsirkulyatsii v teploye vremya goda. Sbornik Problemy Arktiki i Antarktiki, vyp. 2, izd. “Morskoy transport”. . 1960b. Osnovy dolgosrochnykh prognozov pogody. Leningrad, Gidrometeoizdat. GOL’TSBERG, I. A. 1961. Agroklirnaticheskaya kharakteristika zamorozkov v SSSR i metody bor’by s nimi. Leningrad, Gidrometeoizdat. GRIGOR’YEV, A. A . 1956. Subarktika. Moskva, Gosudarstvennoye izdatei’stvo geograíicheskoy literatury. KHROMOV, S. P. 1948. Osnovy sinopticheskoy meteorologii. Leningrad, Gidrometeoizdat. KOPTEV, A. P. 1961. Al’bedo oblakov,vody i snezhno-vodyanoi poverkhnosti. (Trudy AANII, t o m 239.) MISHCHENKO, 2. A. 1962. Sutochayy khod temperatury vozdukha i yego agroklimaticheskiye Snacheniya. Leningrad, Gidrometeoizdat. . 1965. O temperature deyatel’noy poverkhnosti v mikroklirnaticheskikh issledovaniyakh. (Trudy G G O , Vyp. 180.) ORLOVA,V. V. 1962. Zapadnaya Sibir’. Klimat SSSR,Vyp. 4, Gidrometeoizdat. PETERSON, S. 1961. Analiz i prognoz pogody. Perevod s angliyskogo. Moscow, Gidrometeoizdat. POLOZOVA, L. G. ; RUBINSHTEIN, Ye. S. 1963. Sovremennoye izmeneniye klimata. (Izvestiya AN SSSR. Seriya Geograficheskaya, No. 5.)

_-

__

PRIK, Z.M . 1964a. Sredneye polozheniye prizemnykh baricheskikh i termicheskikh poley v Arktike. (Trudy AANII, t o m 217.) . 1964b. Baricheskiye i termicheskiye usloviya v Arktike v period MGSS. (Trudy AANII, tom 266.) _- . 1965. Osadki v Arktike. (Trudy AANII, t o m 273.) RAGOZIN, A. I.; CHUKANIN, K . I. 1961. Napravleniye i skorosti peremeshcheniya tsiklonov i antitsiklonov v Arktike. (Trudy AANII, t o m 235.) RUBINSHTEIN, Ye. S. 1956. Ob izmenenii klimata SSSR za posledniye desyatiletiya. D. I. Veyeikov i sovremennyye problemy klimatologii. Leningrad, Gidrometeoizdat. . 1958. Obrashcheniye sutochnogo khoda ternperatury vo vremya polyarnoy nochi i nochnyye povysheniya temperatury zimoy v urnerennykh shirotakh. Moscow, Izvestiya AN SSSR, seriya Geograficheskaya, No. 3. . 1962. Teployadernyye i besyadernyye zimy. Moscow, Izvestiya AN SSSR, Seriya Geograficheskaya, No. 4. SHCHERBAKOVA, Ye. Ya. 1961. Vostochnaya Sibir’. Klirnat SSSR, Vyp. 5, Gidrometeoizdat. VANGENGEIM, G. Ya. 1961. Predskazaniye sezonnykh raspredeleniy meteorologicheskihk elernentov. Izvestiya AN SSSR. Seriya geograficheskaya, No. 3. ZAKHAROVA, A. F. 1959. Radiatsionnyy rezhim severnykh i yuzhnykh sklonov v zavisimosti ot geogra$cheskoy shiroty. (Uchenyye zapiski Leningradskogo Gosudarstvennogo Universiteta No 269, seriya geograíicheskava.)

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__

__

61

Some features of the microclimate within hilly regions in Finland S. Huovila

T h e weather in Finland varies greatly from day to day and from year to year. This is due to the battle between maritime air masses from the Atlantic Ocean and the continental air masses from Europe and Asia. The annual temperature range can therefore be quite large in s o m e years. As an example, the m i n i m u m temperature in Ivalo w a s -48.60 C o n 1 February 1966 and the m a x i m u m temperature 31.70 C on 20 June 1966. T h e annual variation of screen t e m perature can thus exceed 800 C in northern Finland and 700 C in southern Finland. The rate of incoming solar radiation is highly variable from season to season in different parts of Finland. In Table 1 w e see that practically no radiation is received from the sun at latitude 700 N.in December and January. At this time the earth surface loses heat continuously owing to long-wave terrestrial radiation. The effective heat loss reaches its m a x i m u m during cloudless weather. The coldest winter temperatures are thus observed during clear, calm days under the influence of cold continental air masses. Near to the ground we can often read temperatures that are m o r e than 100 C colder than the simultaneous reading in the thermometer screen. In June, northern Finland receives considerably m o r e solar radiation than southern Finland during cloudless days. If the w a r m continental air from eastern Europe enters northern Finland, we can expect very w a r m days at those latitudes. Table 1 also reveals large differences in the a m o u n t of solar radiation received by surfaces of different slopes and directions. In the springtime walls and slopes facing south receive m u c h m o r e solar radiation than horizontal surfaces and about ten times more than the north-facing walls and slopes. This unequal distribution of short-wave radiation results in the early melting of s n o w and awakening of life forms o n the southern slopes of hills and mountains during

sunny days. D u e to the midnight sun the distribution of solar radiation is m u c h more uniform in the middle of the s u m m e r , especially in northern Finland. Actually, northern slopes have been found to be safer than southern slopes from d a m a g e caused by radiation frost in northern Finland. T h e reason for this paradox is that the northern slopes also receive solar radiation during clear nights or in a situation that is favourable to radiation frost. With dense vegetation in the middle of the s u m m e r , too, the height and the density of the vegetation are more important from a microclimatological viewpoint than the slope and direction of the surface. It must be pointed out that this rule is only valid for s u m m e r days, not for nights. At night, the relative temperature of a given point in a hilly region is determined mostly by the relative height of this point compared with its surroundings a n d the thermal conductivity of the soil at this point. Since cold air is heavier than w a r m air, the coldest air is liable to flow iato deep pits and valleys and the warmest air is found at the hilltops. This kind of t e m perature distribution is most evident during calm, cloudless nights in both s u m m e r and winter. Figure 1 shows the temperature distribution measured at a height of 1.7 m above the ground along an old main road in central Finland during four clear and calm nights in August 1963. Temperature readings were taken at 91 different measuring points along the road during outward and return journeys m a d e in a car. T h e length of the route w a s 33.2 km. The correlation between relative temperature and relative height is quite obvious. This means that the temperature on a hilltop is generally w a r m e r than the temperature in the neighbouring valley at the s a m e height above the ground. T h e best correlation, however, is to be found between temperature curves recorded during different nights. The conclusion to be drawn is that every point within a certain small area has a fixed relative

63

S. Huovila

TABLE1. Diurnal amount of solar radiation (direct solar radiation plus sky radiation) on various surfaces during clear days, measured on the fifteenth day of each month. Unit: kcal/m2. (Based on data from Lunelund, 1940) Surface

Jan.

Feb.

Mer.

Apr.

390 400 2 060 55 1470 60 1710 95 425 1260 95

1160 1040 3 585 105 2 640 175 3 265 190 1230 2 550 260

2 500 1935 4 380 165 3 505 515 4 730 305 2 415 3 975 880

4 290 2 840 4 120 350 3 935 1220 5 690 740 3 905 5 220 2 140

5 720 3 435 3 540 930 3 835 1990 6 045 2 330 4 990 5 900 3 330

-

320 420 2 O00 55 1430 55 1595 90 420 1220 90

1480 1535 3 975 135 3 115 385 3 750 240 1685 3 050 530

3 440 2 935 4 420 440 4 150 1340 5 300 710 3 525 4 850 1800

5 360 3 935 4 220 1800 4 315 2 610 6 150 2 400 5 050 5 960 3 355

May

July

Aug.

Sept.

Oct.

6 350 3 590 3 i50 1400 3 595 2 360 6 045 3 385 5 405 6 015 3 945

5 930 3 385 3 185 1150 3 560 2 120 5 920 2 860 5 060 5 785 3 585

4 730 2 900 3 600 535 3 650 1470 5 590 1275 4 150 5 255 2 535

3 180 2 215 4 080 205 3 525 780 4 920 390 2 915 4 310 1345

1660 1330 3 820 135 2 875 27 5 3 755 245 1625 3 035 460

600 575 2 570 75 1840 80 2 170 130 655 1650 130

6 470 4 330 3 965 3 170 4 225 3 630 6 415 4 170 5 865 6 330 4 745

5 920 4 065 3 965 2 650 4 130 3 205 6 195 3 435 5 395 6 030 4 165

4 240 3 300 4 160 880 4 140 1795 5 555 1335 4 130 5 250 2 440

2 280 2 085 4 190 180 3 540 700 4 415 335 2 415 3 800 985

740 860 2 950 90 2 155 135 2 540 155 895 1960 215

25 50 430 10 340 10 325 15 45 270 20

June

Nov.

Dee.

Latitude 600 N.

Horizontal surface W.and E.wall

S. wall

N.wall S W . and SE.wall NW.and NE.wall S.slope 450 N.slope 450 W . and E. slope 450 SW.and SE. slope 450 N W . and NE. slope 450 Latitude 700 N.

Horizontal surface

W.and E.wall

s.wall

N.wall SW.and SE.wall N W . and NE.wall S. slope 450 N. slope 450 W.and E.slope 450 SW.and SE.slope 450 N W . and NE. slope 450

-

-

minimum temperature durine calm, clear nights, v provided that the vegetation and thermal conductivity of the soil do not change greatly and that all the measuring points lie within the same air mass. In other words :if point A is warmer than point B a clear, ill be warmer than B during every calm, calm night,A w clear night as long as A and B are situated at the same height above the ground and the conditions above are fulfilled. Figure 1 also tells us that serious mistakes can be made under certain conditions if ordinary methods are used for the reduction of meteorological data. An ordinary method of adjusting temperature observations is to subtract 0.650 C for an increase of 100 m in the altitude. This rule would lead to completely false results in regions where the hills are some tens of metres high, like those in Figure 1. For example, point No.35 was situated at a relative height of 40 m and point 36 at a relative height of 71 m. The temperature difference between those points was negligible o n clear days whereas point 35 was 7.10 C colder o n clear, calm nights, as a mean of the trips 2, 3 and 4. The daily mean temperature at point 35 is also several degrees colder than at point 36 but, point 36 would be colder if w e used the rule which is valid for big differences in the altitudes within high mountains. The effectof hills on the distribution of precipitation is not yet completely understood, but it is being

64

250 280 1615 40 1150 40 1265 70 280 940 70

-

-

-

-

-

studied both in Sweden and in Finland. As pointed out earlier, the distribution of solar radiation is unequal on different surfaces in spring and the rate of decrease of the snow cover is thus considerably higher on southern than on northern slopes. Cooling during clear nights is a reason for the ample formation of dew and fog in valleys but no data are available on the amount of d e w in Finland. The wind speed in Finland is generally very low during summer nights. Several studies have revealed that a wind speed of 0.5 m/s or less is very typical in central Finland on clear nights. This value refers to the screen height (2 m above the ground), while 1-2 m/s can be observed at the anemometer height during a night. This calmness of clear nights often results in damage by radiation frost. The experience of farmers from olden times agrees fully with the results shown in Figure 1 and, for this reason, farms in northern and north-eastern Finland are situated mostly on hilltops. T o s u m up w e can say that microclimatological conditions play an important part in Finland. A knowledge of these conditions is most important in hilly regions,especially in northern and north-eastern Finland. The influence of solar radiation, the distribution of temperature during clear nights and the properties of the snow cover are among the most important microclimatological factors.

S o m e features of the microclimate within hilly regions in Finland

"""

I""""'I""""'I""""'~""""'~""' 10

lo

20

30

50

40

60

'

'

I

70

'

'

"

'

1

~

~

'

l ' ' ' ' ' i I r i l '

80

90

IO

3

'C

Fig. 1. Temperature curves during four nights (1-4) and the mean curve of nights (2-4). Horizontal scale: measuring points. Bottom curve (h): relative altitude.

Résumé Quelques caractéristiques du microclimat dans les régions accidentées de Finlande (S.Huovila)

L'influence des accidents de terrain sur la distribution des températures pendant l'année est manifeste. Pendant le jour, la pente d u terrain joue un rôle déterminant dans l'intensité du rayonnement solaire et la température du sol. Pendant les nuits claires et calmes, d'autre part, la descente de masses d'air froid et lourd dans les vallées et les dépressions peuvent provoquer d'importantes différences entre les températures minimales. Supposons que des mesures soient effectuées en deux points d'un m ê m e village situés à des altitudes différentes au-dessus d u niveau de la mer, mais à une

certaine hauteur au-dessus du sol. I1 n'est pas du tout exceptionnel de trouver des différences de l'ordre de 10 O C entre les températures minimales de ces points pendant une nuit claire et calme. P a r m i les effets secondaires de ces phénomènes, signalons l'abondance de rosée et de brouillard que l'on observe en m ê m e temps dans les vallées. L'orographie et la pente du terrain influent égalem e n t sur les précipitations, ainsi que sur l'accumulation et la vitesse de diminution de la couche de neige. L a distribution des vents, en direction et en vitesse, dépend aussimdu relief, et les nuits sont souvent très calmes dans le centre de la Finlande.

Discussion F. E. ECKARDT. Pourriez-vousindiquer le type d'instrument utilisé pour la mesure du rayonnement?

S. HUOVILA. Table 1 is based on data of Lunelund (1940). H e carried out a long series of observations in the years 1922

to 1939 by using Gorcaynskipyrheliagraphs, Angström pyranometers, Bechstein photometers and several other instruments. At that time, Lunelund was one of the best experts in the study of short-waveradiation and he published m a n y papers on solar radiation and illumination.

65 5

S. Huovile

Bibliography / Bibliographie HUOVILA, S. 1963. Some features of the microclimate of a luxuriant turnip rape field on a clear day. 20 p. Geopfiysica, vol. 6, no. 3-4. . 1964. O n precautions against crop damage due to radiation frost within hilly regions. 22 p. Soe. Scient. Fenn. Comm. Pfiys.-Matfi.,vol. XXIX,no. 4. LUNELUND, H. 1940. Bestrahlung verschieden orientierter Flächen in Finnland durch Sonne und Himmel.27 p. Soc. Scient. Fenn. Comm. Pfiys.-Matfi., vol. X,no. 13.

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66

SEPPANEN,M. 1963. On the influence of the amount of snow, slope of terrain and position of trees on the rate of decrease of the snow in pine-dominated forest. Geopfiysica, vol. 8, no. 3, p. 213-224. VALMARI, A. 1966. O n night frost research in Finland. Acta Agralia Fennica, no. 107, p. 191-214.

Radiation measurements near the forest limit in northern Sweden Hans Odin and Kurth Perttu

OBJECTS O F T H E INVESTIGATION T h e climate at the forest limit, i.e., in the boundary regions between mountain and forest country, constitutes a limiting factor o n the expansion and regeneration of the forest. Radiation is one of the primary factors affecting the exchange of heat a n d moisture between the atmosphere and the surface of the ground with-its vegetation. T h e objects of the present investigation were : 1. T o determine the albedo of different types of terrain such as treeless mountain plateaux, clearings and forest, thereby obtaining data on the quantity of absorbed radiant energy. 2. T o compare the total radiation exchange of the ground at a single locality o n a cloudless s u m m e r day, both in a clearing and infjeld forest. 3. T o estimate the difference in available energy between clearing and fjeld forest with respect to energy other than radiation, e.g., in the form of evaporation and turbulent heat transfer. T w o approaches to the problem were adopted, namely measurements m a d e from aircraft, this m e t h o d permitting large areas to b e surveyed, and measurements at ground level. T h e measurements from the air gave clear readings, as did those m a d e o n level, treeless terrain, whereas the measurements m a d e in forest country were extremely difficult to interpret owing to the complex system of radiation.

MEASUREMENTS M A D E F R O M AIRCRAFT T H E O R Y A N D PRINCIPLES

Incident short-wave radiation and short-wave radiation reflected from the ground, i.e., energy in the w a v e -

length interval from 0.3 to 3 p m , were measured from a n aircraft. T h e energy w a s measured in gcal/cma/min or in ly/min. Figure 1 represents conditions o n a cloudless s u m m e r day. Diffuse sky radiation (D)comprises about 20 per cent of the total incident short-wave radiation (global radiation). T h e ratio between G, a n d G is called the albedo a n d is designated A. This expression thus indicates the proportion of incident short-wave radiation reflected from the surface of the earth. T h e radiation varies with the fligh alttitude (page 68). T h e albedo can however be regarded as constant with the height above the ground, since the increase in global radiation with height above the ground is balanced by the increase in radiation reflected from the atmospheric layer between the ground a n d the aircraft. This is supported by the results.

G

D

. I sin h

Short-wave radiation 0 . 3 - 3 ~

FIG.^. Components of short-waveradiationat asmoothsurface. I sin h = direct solar radiation (h = sun-altitude) D = diffuse sky radiation G = global radiation Gr = reflected global radiation.

67

H.Odin and K.Perttu

INSTRUMENTS A N D MEASURING TECHNIQUE

T h e instruments used consisted of t w o Moll-Gorczynski Solarimeters, one directed u p w a r d a n d the other d o w n w a r d . These measured radiationin the w a v e length interval from 0.3 to 3 p m . T h e Solarimeters were m o u n t e d at the wingtips in place of navigation lights o n a n aircraft of type Sk 16 provided by the Swedish Air Force. Cables running along the wings and into the cabin were connected to a millivoltmeter. Either Solarimeter could be connected to the voltmeter as desired by simple manipulation of a switch. T h e orientation of the Solarimeters w a s almost exactly horizontal w h e n the aircraft w a s in flight, In the following description, any deviations of the meters from the horizontal position have been ignored. Changes in the altitude of the aircraft with variations in air speed are similarly disregarded. T h e instruments w h e n in operation are influenced (Fig. 2) by radiation over the entire aperture angle of 1800. Radiation from the area near the horizon is however small compared to radiation from the area about the zenith, provided that the sun is not low in the sky. T h e ground area from which the radiation is received is therefore assumed in the following to have a magnitude of x(H/tg20)2 (Fig.2). Measurements from the air were m a d e over different types of ground, principally clearings, forests and treeless mountain plateaux. Owing to the reaction time of the meters (about 20 seconda from zero to full deflection), the course of the aircraft w a s laid so as to traverse similar ground for fairly long periods. In measurements m a d e at low altitude, repeated passes were m a d e over the s a m e terrain in order to obtain data for calculation of the m e a n albedo of the terrain.

Instrument

---

Horizontal plane

Ground //rt////////////////////////y/ /

TI.

["I2

tg

20

FIG. 2. Relation between the height of the instrument above ground surface from which the principal part of the measured radiation is received.

T h e flights covered a region extending from Östersund in the south to Gällivare in the north and from Enafors in western Jämtland in the west to Luleå

in the east. T h e y were m a d e at different altitudes above ground level, from 100 m to 1,500 m.T h e speed of the aircraft w a s 180 k m / h r at 100 m and 230 km/hr at other altitudes. MEASUREMENTS

T h e flights were m a d e o n 15, 16 and 19 July 1965 and are illustrated in Figures 3-8.In these, the time is laid off along the abscissa and the radiant energy in ly/min along the ordinate. Percentages for albedo are plotted at the top of each graph. T h e first measurement (Fig.3), which w a s a trial run, w a s m a d e over the Luleå area. T h e sky w a s cloudless while the measurements were being m a d e ,

O

20- Co 15 *

0 Moo.

-

10 5-

F

o.m. 0.10-

till

I

;,

1l;l III' 'III

I

111; IlII

I

0.50-

I

0.40-

I I

0.10

I

I

I I I

I I

o 20-

I

Ilil IIlI III :III 1111

I

0.60-

0.30

------------3

._._._._._._._._._.

100.

0.m

8

I I I I

I I I ' I I I I

;I;

I I I

I i I

I I

1 ; '

I

i¿i

pl, 111

; :I";i I l

A

o m

- --

FIG. 3. Flight near Luleå, 15 July 1965. . global radiation, i. e., incoming short-waveradiation measured global radiation O measured reflected radiation albedo B: bog; Co: concrete; F: forest;

Radiation measurements near the forest limit in northern Sweden

FIG.4. Flight Luleå-Gällivare, 16 July 1965. Code as for Figure 3. C: clearing; T:treeless mountain plateau.

16- Albedo i % 1514-

13-

1211-

10-

' F

0.900.80-

0.700.600.500.40.

0.300.200.10

0-

FIG. 5. Linalompolo, 21 July 1965. Global radiation ( ), reflected radiation (---) and albedo (top), at 1.6 m above ground.

.T.

lo

I

0.30

except o n t w o occasions w h e n small cumulus clouds h and 10.40affected the radiation input (10.05-10.07 10.41 h). T h e dot-dash line represents the radiation that would have prevailed in clear weather conditions. Flight altitude w a s 200 m except in the case of the first reading, which w a s taken over concrete prior to take-off. T h e second measurement (Fig 4) w a s m a d e between Luleå a n d Gällivare at a height of 500 m, and over Linalompolo, 25 k m north-west of Gällivare, at a height of 100 m. During the flight the global radiation rose from 0.80 ly/min (or gcal/cmz/min) at 08.15 h

to 0.87 ly/min a n hour later. Unfortunately, cumulus h a d begun to build up over Linalompolo, so that the global radiation is assumed to correspond to the dotdash line except at 09.06 h, w h e n both the aircraft and the ground were overshadowed by the s a m e cloud. On this occasion, however, the upward-facing meter did not have time to adjust to the true global radiation, and the albedo consequently c a m e out too low. Other measurements showed that the albedo increased in the shade (Fig.5), 12.06 h-12.35 h). T h e third flight w a s m a d e between Luleå and Enafors, with touchdowns at ûstersund o n both the

69

H.Odim and K. Perttu

Albedo i %

6. Flight Luleå-Ostersund, ' ' FIG. tude 500 m, 19 July 1965. global radiation

e

:

F e

L

O! 0945 0950 0455 Lat 65.3 Lon2

20.9

1600

1005

1090

10)s

65.0

64.7

20.2

19.1

t:

1020

1025

10'30

64.5 18.6

10'75

13'40

alti-

0

reflected radiation albedo B: bog; C: clearing; F: forest; L:lake.

M.E.T.

1Ó"5 64.2

17.3

FIG. 7. Flight Östersund-Enafors-ÖsterSund, 19 July 1965. F: forest; T:treeless mountain plateau.

M.E.T. 600 rn altitude

outward and return trips. Figure.6 shows the measurements m a d e between Luleå a n d Ostersund at a height of 500 m. In Figure 7, which is a record of the flight from Östersund to Enafors, it can be clearly seen h o w the global radiation varies with the height of the meter. A t a n altitude of 550 m the radiation w a s 0.96 ly/min, while twenty minutes later, at 100 m, it w a s 0.92 ly/ min, and fifteen minutes after that, at 600 m, it w a s 0.94 ly/min. T h e fact that the incident radiation

70

during this last part of the flight did not reach the s a m e figure as during the first part w a s due to the general fall-offin incoming radiation during the afternoon. As in Figures 3 and 4, the dot-dash lines in Figure 7 indicate the global radiation that would have prevailed in clear weather. T h e albedo over different types of terrain is computed from the corrected global radiation and from the reflected radiation over sunlit areas. T h e Hight from Östersund to Luleå w a s m a d e at a n

Radiation measurements near the forest limit in northern Sweden

FIG.8. Flight Ostersund-Luleå,19 July 1965.Global radiation ( radiation

-

), reflected .

(--) and albedo (top).

ecIia 16 14

12 10 Ob0

0.70 0.60

0.50 OM

o.sa 0.M

1625

16”

163,5

lbk5

16”

1705M.E.T.

1,500rn altitude

altitude of 1,500 m. T h e decline in incident radiation during the afternoon is clearly apparent from Figure 8. T h e small variations in the curve are due to cirrus clouds which partly obscured the sun from time to time. The incoming radiation showed a m u c h greater percentage drop than the reflected radiation, with the result that the albedo rose during the afternoon. The sharp rise in albedo, e.g., between 16.20 and 16.30 h, w a s caused by a fall in incoming radiation due to clouds which concealed the sun, while the reflected radiation remained constant or even rose slightly. T h e surface of the ground viewed from an altitude of 1,500 m presented a fairly uniform appearance over the whole route, so that no division w a s made. It consisted for the most part of forest, bogs, clearings and small lakes. With a 1400 aperture angle, reflection readings are obtained from a n area with a diameter of over 8 km. R E S U L T S A N D D I S C U S S I O N (see T a b l e

1)

The

albedo over coniferous forest varied from 10 to 13 per cent. Over Linalompolo, near Gällivare, the albedo w a s 10-11per cent, whereas over Enafors, four degrees further south, it w a s 13 per cent. The albedo figures for clearings were 14-16per cent. Bogs, moors and treeless mountain plateaux showed the s a m e albedo as clearings or s o m e w h a t higher. W a t e r surfaces (the Gulf of Bothnia and L a k e Ctorsjön) had a low albedo and showed great variations at different times; this is because the albedo over water is dependent o n both solar altitude and the smoothness of the surface.

MEASUREMENTS M A D E AT G R O U N D LEVEL Meteorological phenomena, including radiation, are continuously recorded at a micrometeorological station at Linalompolo. For the purpose of studying radiation conditions in forest as compared to clearings, measurements were m a d e with portable instruments as a supplement to the measurements m a d e from the air. The measurements described below were m a d e o n 18 July 1965 between 10.30 and 16.55 h. T H E O R Y A N D PRINCIPLES

The ground

measurements, like those m a d e from the air, comprised the short-wave interval (0.3-3 pm). Measurements were also m a d e of the radiation balance, i.e., the difference between incoming and outgoing radiation. This comprises both short-wave and longw a v e radiation (0.3-60pm). The components of the short-wave radiation o n level, treeless ground are identical with those s h o w n in Figure 1. Figure 9 also shows the long-wave components (wavelength interval 3-60pm). The long-wave radiation from the atmosphere (Ea) is of the order of %E,. o n a cloudless day. The radiation balance Eb is expressed by the formula (1 - A)G - Eeff,where (Liljequist, 1962): Eb (1 A)G = global radiation absorbed by ground G,/G albedo, and Eeff effective surface, A long-wave radiation from the ground. The effective long-wave radiation from the ground can for example be computed from Angetröm’s formula = cTo4f(eo), where f(eo) = (Liljequist, 1962): Eeff a + b + 10-ce0, To= temperature in OK at instrument

-

=

=

=

=

71

H.Odin and K.Perttu

TABLE1. Albedo, from measurements by aircraft over different types of surface Location rind altitude

Near Luleå 200 rn

Surface

Concrete Meadow Bog Coniferous forest Sea Coniferous forest and bog Clearings Treeless mountain plateau Treeless moor Lakes Forest with bare patches

221 13 14 12 3-5

Luleå-Gallirare 500 rn

Linalompolo 100 m

Luleå Ontersund 500 m

10-11

10-11

15 10-11

12 14-15 15-16

OsteruundEnafors-Ontersund 500-600 m

12-13 4-8a

Enefors 100 rn

13

14 14-16 16-18

17 6-7 14-16

1. Measured on the ground. 2. Lake Storsjön.

altitude, eo = vapour pressure in millibars at instrum e n t altitude, and a, !'

A

O #AR

ir-

WHITE SPRUCE/ BLACK SPRUCE 4

2

I

6 A?R

IO 12 14 16

8

1

MAY

1

JUNE

I

150 18 2 1 O c JUL

1

AUG

I

SEP

OC

I

oc1

I

NOY

1

DEC

I

JAN

1

FEE

OF

eo 20 60 10 40

O 20 -10

-20

-1-1

WILLOW WHITE SPRUCE/BLACK SPRUCE

O

-30

20

-40

40

-50

60

FIG.8.Average weekly temperaturesforthewillow and white spruce/blacksprucestandsfrom 1 October1964to 30 September1965.

230

Soil temperatures in river bottom stands in interior Alaska

FIG.9. Snow depth for the willow and white spruce/black spruce stands.

cm MAR 55..

1

APR

I

MAY

I

JUNE

I

JUL

1

AUG

1

SEP

1

OCT

I

NOV

1

DEC

I JAN I

I

I

FEB

0 WILLOW WHITE SPRUCE/BLACK SPRUCE

I

depths were at a m a x i m u m in late December and decreased throughout the rest of the winter due to packing and sublimation.

CONCLUSIONS

,

Differences in the soil temperature régime in the four river bottom stands can b e related to t w o factors: texture of parent material and thickness of the insulating organic layer. Older stands o n the flood-plain s h o w thick deposits of fine alluvial silt deposited during flooding. Frost penetration and thawing are slower in finer deposits than in coarser deposits because finer deposits hold m o r e water and thus m o r e latent heat of fusion is contained within the soil (Geiger, 1965). Permafrost is m o r e likely to occur closer to the surface in fine than in coarse soils. Changes in plant cover effect changes in soil temperatures. T h e insulating effect of the accumulated moss or organic layer is the most significant difference a m o n g stands. B r o w n and Johnston (1964)report that the thermal conductivity of dry peat is 0.0017cal/cm/oC/sec whereas that of saturated frozen peat has a conductivity of 0.0056 cal/cm/0C/sec. T h e thick organic layer a n d moss layer in the spruce stands in this study should have a thermal conductivity close to that of peat. During the w a r m periods in the s u m m e r the organic layer dries, resulting in l o w thermal conductivity, thus preventing heat penetration into the soil. In the autumn, the organic material becomes saturated by a u t u m n rains. W h e n frozen in winter it acts as a better thermal conductor than w h e n dry in s u m m e r . T h e thick organic layer thus allows m o r e heat transfer in winter from ground to atmosphere than in s u m m e r from atmosphere to ground. Soils with a thick organic layer are colder during s u m m e r than those with a thin or with no organic layer. An insulating moss layer helps

l

I

l

l

to maintain a permafrost layer in m a n y soils in the boreal region. T h e successional development of vegetation, especially the development of a thick moss mat, produces colder soils a n d eventually permafrost. T h e frozen soil prevents water percolation and the resulting wetter soils inhibit tree growth while favouring further moss development. Ultimately fast-growing timber stands along the rivers give w a y to slow-growing black spruce a n d bogs, the t w o most prevalent vegetation types o n permafrost soils.

SUMMARY 1. T h e soil temperature régimes in the four stages of river bottom succession are significantly different.

2. Soil froze earliest and deepest in early successional stages a n d later and less deep in later successional stages, T h e insulating effects of a m o s s layer and the presence of finer river alluvium probably account for slower freezing in the spruce stands. 3. M o r e s n o w accumulated in earlier successional stages, though freezing w a s faster and soil temperatures colder in these stands. 4. Large differencesin time of thawing occurred between the stands. In the earliest successional stage thawing w a s completed by the end of M a y , whereas in the oldest stand, thawing did not begin until the end of M a y and w a s never completed, a continuous frozen layer being present between 55 and 80 c m . 5. Fluctuations in soil temperatures are most rapid and greatest in the willow stage and are less rapid and of less magnitude in the later successional stages. 6.Soil temperatures during the growing season are warmest in the earlier stages of succession and colder in the later stages.

231

L. A. Viereck

Résumé L a température du sol dans les peuplements forestiers du fond des vallées à l’intérieur de l’Alaska (L. A. Viereck)

On trouvera dans cette étude des comparaisons entre la température d u sol à quatre stades différents et l’évolution du peuplement forestier dans la vallée de la Chena, près de Fairbanks, Alaska. On a enregistré la température du sol à des profondeurs de 5, 10,20, 50,100 et 150 c m dans un peuplement de saules ( S a h alaxensis Cov.), sur un banc d e gravier récemment mis à découvert, un peuplement de peupliers baumiers (populus balsamijera L.)de cinquante ans, un peuplem e n t d’épicéas (Picea glauca (Moench) Voss) vieux de cent vingt ans, et un peuplement mixte de deux variétés d’épicéas - Picea glauca et Picea mariana (Mill.) B. S. P. de deux cent vingt ans. On a constaté qu’au cours des premiers stades de l’évolution, le sol gèle plus vite et plus profondément et atteint des tempéra-

-

tures plus basses qu’aux stades suivants. L a plus grande différence de température d u sol entre les peuplements a été observée pendant le dégel et pendant la période de croissance des plantes. D a n s le peuplement de saules le dégel était terminé à la fin de mai, tandis que dans le peuplement mixte d’épicéas, il n’a pas c o m m e n c é avant la fin de m a i et n’a jamais été total, u n e couche gelée continue s’étant maintenue à une profondeur de 40 à 80 c m . Pendant la saison de croissance, les températures à 10 cm de profondeur ont atteint les m a x i m u m s suivants : saule, 22%; peuplier baumier, 14% ; Picea glauca, 9oC ; Picea mariana, 2%. L’action isolante d’une épaisse couche de mousse et de dépôt d’alluvions fluviales microgrenues explique sans doute le refroidissement plus lent et le dégel plus tardif dans les peuplements d’épicéas, par rapport a u x peuplements de saules et de peupliers baumiers.

Discussion J. MALAURIE. Avez-vous observé une stratification sur le plan de l’humidité de la surface du sol à la table du permafrost ? E n terre de Hall, il a été noté qu’il est une zone intermédiaire peu humide constituant du point de vue de la diffusion thermique c o m m e un “ coussin protecteur” (cf. Davies Greeland Symposium, Copenhague). D’autre part, et cela est un peu en dehors de votre c o m m u nication, avez-vous mesuré les temps et température lors de la surfusion de l’eau vive des rivières de Fairbanks (abord du Campus) ?

L. A. VIERECK.I have only one set of soil moisture units in place above a permafrost layer. The soil above the frozen layer remains wet during the summer because the water cannot penetrate through the frozen layer and because evaporation from the moss layer is low. I have attempted to observe if there is a migration of moisture to the freezing layer in the autumn but have not recorded any dehydration of the surrounding layers. Perhaps the “thermal cushion” that you mention occurs under very different circumstances from that which I have studied in interior Alaska. No, I have made no measurements of the temperature of the water in Alaskan rivers. I believe that Dr. Benson of the Geographical Institute of the University of Alaska has

232

recorded super cooling of river waters during the period of freezing.

C. O. TAMM.Nobody will question your statement that a thick m o s s layer is a better insulating agent when dry than when in a wet condition. However, I have a suspicion that speaking of thermal conductivity as the decisive factor m a y he an oversimplification. W-hile summer heating m a y be mainly a question of incident radiation and conductivity of the soil material, it seems at least possible that cooling by mass flow of cold air near the ground and into soil cavities m a y play some role, until the ground receives a thick snowcover. I should welcome a strict physical analysis of the heat transport in soils beneath different canopies (with their characteristic patterns of snow accumulation).

L. A. VIERECK. I agree with you that there is undoubtedly more involved in the effects of the moss and organic laver in the transfer of heat to 2nd from the soil than its thermal conductivity. The cooling effects of the evaporation of moisture from the moss surfaces as a result of transpiration is one of these. In years of late snow-fall,movement of cold air near the ground m a y be important but in interior Alaska, where snow usually remains on the ground from October to late April or M a y and where winds are very light,its effects m a y not be very great.

Soil temperatures in river bottom stands in interior Alaska

Bibliography BENNINGHOFF, W. S. 1952. Interaction of vegetation and soil frost phenomena. Arctic, vol. 5, p. 34-44. BROWN, R. J. E.;JOHNSTON, G. H . 1964. Permafrost and related engineering problems. Endeavour, vol. 23, p. 66-72. COLMAN,E. A.;HENDRIX, T. M. 1949. The fiberglas electrical soil-moistureinstrument. Soil Science, vol. 67, p. 425-438. DRURY, W. H. 1956. Bog flats and physiographic processes in the upper Kuskokwim region, Alaska. 130p. (Contr. to the Gray Herbarium, No. 178.) FRASER, J. W. 1961. A simple instrument shelter for use in

Bibliographie Forest Ecology studies. 10 p. (Canada Dept. of Forestry,

Tech. Note no. 113.) GEIGER, R. 1965. The climate near the ground. Cambridge, Mass., Harvard University Press. 611 p. PERCIN, F. DE. 1960. Microclimatology of a subarctic spruce forest and a clearing at Big Delta, Alaska. 162 p. (Quartermaster Res. and Eng. C o m m a n d Tech. Rpt. E. P. 130.) PÉwÉ, T. 1957. Permafrost and its effect on life in the North. Arctic Biology, p. 12-25.Oregon State College.

233

On the study of the ecology of subarctic vegetation I. Hustich

It is not easy to decide h o w to present such a broad and general subject as the ecology of subarctic vegetation. If I were a more modest m a n I should talk today only about some details, which I have studied during recent years; a more concrete observation, regardless of h o w small, always seems more useful than attempts to generalize things which perhaps are already vaguely defined. However, as a basis for discussion-and that is the main reason why w e are meeting here-I will try to present subjectively some features concerning the study of subarctic ecology. The first thing is to define the words “ecology” and “subarctic”. Regardless of the fact that so m u c h research has been done in ecology, it is still necessary to explain what it is: “Plant ecology” is a general term to cover the study of the plant/environment relationship, and in particular the importance of this relationship for the development and production of species and vegetation units with regard to habitat and regional distribution. I have, as you notice, slightly modiíied a well-known and generally accepted definition of the concept ecology by adding the word “production”, which is significant for modern ecological research. The word production is not here restricted to the applied science aspect; I have used it to give added importance to a significant quantitative tool, even if the word production in this respect should need some clarification itself. M u c h is thus crammed into this science. However, the ecological approach,regardless of “pure” or “applied”, w ill be more important in the future than at the present time. When, as seems to happen quickly just now, the relationship of m a n to his environment changes from being an interesting scientific question to an urgent need of knowledge for a mankind having to live on an overcrowded globe, ecology (or better

the ecological sciences) will certainly be more and more in the foreground. By this I do not want to advance a n e w “environmentalism” or a “determinism” of the rigid kind which is still to be found among some geographers. I have simply stressed the necessity to know the ecological mechanism not only between plant growth and an environment more or less untouched by man-as is still the case in large parts of the Subarctic-but also between plant growth and an environment which has been greatly modified or perhaps entirely changed by man. W e admit, if w e are honest, that phytogeographers have generally considered an environment, which has been greatly modified by man, as a “secondary” object of study compared with the natural or virgin environment. And what is the Subarctic? I must confess that it is rather interesting to take part in a symposium in which no one seems to k n o w exactly what the subject (i.e. Subarctic) really is and where everyone seems to have his o w n definition. The following is a definition which is very m u c h my o w n and which unfortunately is not commonly accepted: the Subarctic in a truly phytogeographic sense is the forest tundra, it is the narrow (or indeed very broad in some places of Siberia and Canada) “ecotone” beween the polar tree line and the boreal forest region proper. Lately,and particularly during the preparation of this symposium, I have noticed that m a n y scientists like to push the southern limit of the Subarctic more to the south,i.e., to the vaguely defined line where the closed or the continuous boreal forest begins; I refer to Professor Mikola’s paper on subarctic forests presented at this symposium. I also greatly appreciated Professor Blüthgen’s careful compilation of the relevant literature regarding this complicated question. I propose that w e push this need of clarification forward by bringing together (it could be done by, for instance, the Arctic

235

‘

I. Hustich

Instituteor Unesco) a few scientistsfrom differentparts of the Subarctic to work out a definition of the concept “subarctic”, a definition upon which later w e could all agree. As the definition in itself indicates the problems of ecology are in principle the same everywhere on the globe. But in each phytogeographical region, such as in the Subarctic,special factors operating in the environment come into focus.How can w e otherwise define these regions? (It seems that w e always need a classification and that our workis mostlylimitedto altering or even demolishing classifications made by others.) Regardless of h o w w e defineit the subarctic has-so it seems for me-been neglected compared with the quantity of biological research which has been done, for instance, in the Arctic. One reason, psychological, is that the Arctic is generally a more beautiful and interesting area than the Subarctic; also from the botanical point of view, particularly phytocenologically, it seems more clear-cut and, therefore, easier to investigate. Until recently,some parts of the Subarctic,northern Scandinavia, Finland and parts of the European U.S.S.R., have been more investigated than extensive parts of North America and Siberia, where w e can still find some of the largest biologically and geographically unknown “middle north” areas in the world. F r o m an ecological point of view, however, this regionally uneven localization of research is not of such a great importance.The subarcticbelt is in general very similar from east to west. A field biologist w h o has been working, let us say, in northern Europe and Canada, can observe almost at once this great similarity the two subarctic areas which are so far apart. This is not only true of the isolated mountains (cf. for instance, Hustich, 1962) or the shores, it is also true of the main forest types in the northernmost forests. It is thus by no means a mere chance that Cajander’s well-known forest-typesystem, based on the ground vegetation pattern as a key to the productivity of the forest, was easiest to apply in the subarctic parts of North America and Eurasia (cf. Kalela, 1961; Kujala, 1945; Hustich, 1949, etc.). T h e same is also true for other ecosystem theories which have been worked out in the northern regions. Ecological research in one part of the Subarctic can thus be applied quite easily to other parts of the same region, because of the circumpolar uniformity. It can also be done because m a n y species occur over almost the entire Subarctic.Other speciesofimportance in the vegetation are either vicarious, substitution or corresponding taxa: opinions vary considerably as regards the true taxonomical identities of m a n y of these taxa. Field botany should be more concerned with pointing out which species are the c o m m o n ones (and pay great attention to their ecology, because these are the species important in the vegetation and the landscape) and less interested in the often more or

236

less “philatelistical” job of listing the rare plants. However, according to the taxonomists, no single tree species c f the forest tundra (or of the Subarctic) seems to occur both in Eurasia and in North America. This is worth mentioning even if the reason for this might be accidental, due perhaps to the deep-felt respect the taxonomists seem to have for the Bering Strait. (Compare also the numerous ideas on biological and geological links between North America and Europe expressed during a symposium in Iceland in 1962, see Löve and Löve (1963).) F r o m an ecological point of view: which are the significant criteria of subarctic? This depends on h o w w e limit the Subarctic, of course. But pending a definition of the subarctic region which could be more commonly accepted, the following characteristic features must be mentioned: (u) the short growth season; (b) the great annual variations in growth, caused by the annual variations in temperature rather than precipitation; and (c) the duration of the snow cover. These featuresalso mark-but to a more pronounced degree-the arctic and the boreal region; nevertheless, w e can hardly study the ecology of the productivity of the Subarctic without going deep into the three above-mentioned factors. There seems to be no direct correlation between permafrost and other subarctic features. Also, I have not mentioned above the light climate. However, this factor varies, so m u c h within the subarctic region that it cannot be singled out as a typical subarctic feature. In the Subarctic we have “arctic”1ight conditions in northern Norway, at Mackenzie (Alaska), near Taimyr and in other parts of Siberia, where the subarctic region runs close to latitude 710 N. (i.e. up to the polar tree line). South of Hudson B a y and in southern Kamtchatka the Subarctic,on the contrary, reaches south to 500 N.with a light-climateof its own. Nevertheless, there are several interesting studies related to the response of growth and assimilation to the light-climatein differentlatitudes (cf Mooney and Billings, 1961) which are of importance for the understanding of subarctic ecology. A m u c h more typical ecological problem of the Subarctic is the snow cover and its significance for plant and animal life. It is remarkable h o w m u c h plant ecologists have neglected the study of the importance of the snow cover and winter conditions in general; both the zoologists and the foresters have done more in this field. (As a comment to the excellent paper on the snow cover by Mr. W. Pruitt, I should like to point out the difference in approach to this problem between plant and zoo-ecologists.A plant ecologist certainly needs a “time coefficient” as an addition to the snow index presented by Mr.Pruitt. W e must also realize that the varying height of the snow cover does not necessarily imply that the temperature on the ground itself, i.e. in and on the vegetation, varies in the same degree.) The ecological importance of ihe

O n the stiidy of the ecology of subarctic vegetation

snow cover is certainly a subject which deserves more attention than has so far been given to it; such research will have some useful practical applications. It should also add a n e w dimensionto a specific and often neglected sector of plant ecology,i.e. plant phenology. In a subarctic environment this problem cannot properly be understood if w e do not literally dig into the snow and study the winter conditions in general. The Subarctic should form a transition between the boreal forest region and the Arctic. This means that the entire polar tree and forest line as well as the forest tundra problem must be a central object of study also from a purely ecological and pragmatical point of view. Fortunately, m u c h has been done already in this field of research by Renvall, Eide, Heikinheimo, Andreev and others (see literature quoted by Mikola, 1969; Sirén, 1961; Tikhomirov, 1956; Hustich, 1949). Here I will only illustrate the main pattern of the change from the closed forest to the treeless tundra. This northern transition line, or better, transition belt, between the forest and its outposts is one of the main phytogeographical ecotones, comparable in ecological importance to the transition belt between the forest and the desert. The forest tundra (Ljesotundra, Waldtundra), forms in its ecological and “microtopagraphic” details an interesting mosaic pattern. Norin (1961)has pointed out that the forest tundra is more than a simple transition belt; it is a biocenological entity in itself, an opinion which is more or less the same as I have advanced in an earlier paper. The short growth season towards the north and the great influence of temperature as an external growth regulator, are, as mentioned above, two typical features which should be taken into account in every ecological study in the Subarctic. In this respect w e must also remember that the climatic control is of primary importance and the edaphic control of secondary importance for the distribution pattern and the ecology of a species. F r o m the southern margin of the Subarctic to the polar tree line there is an increased “climatic hazard coefficient”, a concept which I introduced twenty-fiveyears ago and which certainly could be more used as a tool in ecologically-directedproductivity research. The climatic hazard coefficient (i.e. the size of the variation coefficientin an annual growth series) clearly increases towards the north. The variations in growth of trees in the forest tundra and in the Subarctic in general correlate particularly well with the annual variations of the July temperature because the growth processes are, in fact, more or less concentrated in this month. It is, however, a rough measurement only, but very intricate multiple regression analyses (see, for instance, Sirén, 1961) also show more or less the same thing. Of course, w e still k n o w too little about the real mechanism (i.e. the physiology of the response of growth to climate. W h a t w e k n o w so far is rather superficial; however, Dr. R. Sarvas’

paper presented at this symposium, introduces some interesting n e w aspects of this problem. The flowering and fructification processes, and also the vegetative growth (thus, including the production of dry matter) of trees and perennials, vary annually in the Subarctic to such an extent that all investigations relating to the productivity of a subarctic area must be carried out for several years if such productivity research is to have any meaning at all. M a n y sins have been and will be committed in this respect. Aspects relating not only to the annually but also to the periodically varying growth (such as the climatic fluctuation in the thirties) must be included in ecological research, particularly in the Subarctic (cf. Erkamo, 1956; Tikhomirov,1956). The need for ecologically correct productivity research has been “in the air” for m a n y years. Now the International Biological Programme has taken up this problem in all its width; it is also a sound idea to let the “Biological Year” cover a period of at least five years (cf. Worthington, 1965, and my comment above). The subarctic region is in general believed to be poor in productivity per areal unit. According to a recent Russian report (Bazilevitch and Rodin (1964) quoted by Ovington, 1966) the production of dry matter in metric tons per year is in the Arctic about 1 ton, in the Subarctic about 5 tons, but in certain more southerly regions over 30-50 tons; these productivity observations are,however, still based on a small material only. Compare in this respect the proceedings of a “productivity symposium” (Lieth, 1962) and for an excellent detail study on the productivity of a c o m m o n subarctic forest moss species, see T a m m (1953). M a n y years ago I illustrated how, in some years, the favourable temperature in combination with the light-climatein northern Finland can allow a production of organic substance as high or higher than in southern Finland,per areal unit. Theoretically, it is in some ways easier to carry out productivity research in the Subarctic than in other regions, except the Arctic. The growth capacity of, for instance, an open one-storied northern forest can easily be measured and its potential more or less forecast. Incidentally, the ecology of lakes and rivers in the Subarctic is a sector worth still more attention even though m u c h attention has recently been focused on such research. The study of the productivity of the lakes-a truly ecological problem of great practical significance-is neverthelessin its infancy in large parts of the Subarctic. The population of the Subarctic, defined earlier according to the “broader” alternative, is probably 8-10million. The area, the “middle north”, to use a recently-coined expression, is thus very thinly populated. This is one reason why a noticeable,and in the long run dangerous, carelessness with nature is the mark of man’s efforts in large parts of the Subarctic.

237

I. Hustich

One is seldom keen to save what one thinks one has more than enough of. W e have started late with the ecological research of m a n y significant land-use problems in the Subarctic. The influence of changes in groundwater level,caused by the construction of large artificial Iakes, is one such problem where lack of co-operation between ecological research and accelerated practical application has been evident. There is also m u c h ecological work still to be done, for instance on the effects ofthe drainage of peat lands. The peat lands of the Subarctic have, however, in contrast to lakes and rivers, been the object of intensivephytogeographic research in northern Europe and the Soviet Union. It is an important tribute to the research activity of earlier phytogeographers that the necessary basic study of morphology and stratigraphy of peat lands started m a n y decades ago; this,. as so m u c h research earlier and later, started with no particular thought being given to its practical usefulness. Today, the theoretical, ecological study of bogs and fens and research as regards their practical use go hand in hand; such co-operative efforts have also started regarding reafforestation in the north. Phytosociology (in a rather orthodox form) was a very popular science in Scandinavia some decades ago. At the beginning the theoretical approach to phytosociology markedly neglected the ecology of the species and the “plant societies”.The reason for the earlier popularity of phytosociology was that in the 1920s and 1930s several university professors just happened to be interested in pure phytosociology. I mention this detail only because w e should not forget such h u m a n factors w h e n discussing the various directions which a branch of science takes at different times in different countries. Today w e can say that ecologicallyill based productivity research is rather modern and w advance, as I hope, rapidly. It must, however, be stressed that w e still need phytosociology or phytocenology as an important primary tool also for an ecologically-directed inventory of the vegetation. Itis time n o w to end the unnecessary friction between the different “sociological” schools and to adopt some general ecosystem classification,at least within a large region such as the Subarctic. Such a classification of subarctic vegetation, if generally adopted, would greatly aid fundamental knowledge of

’

the different regions and give a better basis for produc-

tivity comparisons. During a symposium on forest types and ecosystems, held in Montreal in 1959, I was somewhat concerned with the rather inflexible individual and national attempts-also observed later -to maintain so m a n y different theories and schools in this field. Recently Ovington (1966) said that “comparative measurement in natural and man-managed areas in m a n y parts of the world should greatly improve our understanding of what determines the ‘productivity’ of plants and animals”. I believe that the Subarctic one of the few great reserves of land,fresh air and water which are still untapped on this planet, is a natural area for an increased international research effort and one of the efforts of the final session should be to strongly emphasize this need. I believe that plant ecology is the basic and natural science for such a task. W e need,however, much more co-operation to avoid unnecessary duplication of work; w e need the exchange of students and exchange of ideas on a greater scale than hitherto. The fact that the ecology ofthe subarcticvegetationis in its main features so similar in different parts of the subarctic zone makes these exchanges easier. But ecology, particularly when directed towards productivity research, is a more concrete and experimental science than phytocenology,a fact which gives us greater hope of achieving international co-operationin this field. I a m well aware that 1 have neglected m a n y important aspects-our problem today is so big that it is impossible to cover all sides of the question. A few simple questions for discussion emerge from what I have stated above. 1. W h a t is the subarctic region? 2.Which are the main characteristics of this region? 3. H o w can w e accelerate the study of the ecology of this region? 4.iHow can w e rationalize our terminology so that at least the primary concepts are defined similarly in Eurasia and North America? 5. H o w can we, for instance, standardize ecological equipment (i.e. using more or less the same instrument for the same purpose) and reach a better co-operation between scientists all over the Suharctic?

Résumé Sur l’étude

de l’écologie de la végétation subarctique

(I. Hustich) ’

L’auteur expose que les facteurs mésologiques particuliers dont dépend la végétation dans la région

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subarctique, outre bien entendu les facteurs généraux qui agissent partout, sont : a) la brièveté de la saison de croissance ; b) les grandes variations annuelles de croissance dues aux variations annuelles de température (plutôt qu’aux précipitations) ; c) l’enneigement. En

O n the study of the ecology of subarctic vegetation

raison du caractère circumpolaire de la région subarctique (surtout si l’on n’entend par zone subarctique que la région de la toundra forestière) les recherches écologiques effectuées dans la partie eurasienne de cette zone peuvent être utilisées dans la partie nordaméricaine, et vice versa. Cette étude souligne en outre l’importance de la limite de la forêt, qui constitue l’une des principales “frontières” phyto-géographiques. Le coefficient d’aléas climatiques, qui augmente vers le nord, est une

caractéristique dont les écologistes qui travaillent dans la région subarctique doivent se préoccuper plus qu’ils n e l’ont fait jusqu’ici. L’auteur signale aussi le rôle que joue le P r o g r a m m e biologique international dans l’avancement des études écologiques relatives à la région subarctique, et la large nécessité d’une plus grande coopération internationale en matière de classification phyto-écologique et de recherches sur la productivité.

Discussion F. E. ECKARDT. A u début de votre conférence, vous avez proposé une nouvelle définition du terme “écologie” en faisant intervenir le concept de “productivité ”. Je regrette u n peu cette proposition et cela pour deux raisons. D’tvbord je pense que l’on ne devrait pas augmenter le nombre de définitions de ce terme, qui est déjà utilisé dans plusieurs acceptions différentes. Ensuite, parce que le concept “productivité” est, lui-même,très difficile à définir. Personnellement, je crois qu’il serait raisonnable d’employer le t e r m e