Evolutionary Dynamics of Forests Under Climate Change

Evolutionary Dynamics of Forests under Climate Change

Claire G. Williams

Evolutionary Dynamics of Forests under Climate Change

Claire G. Williams National Evolutionary Synthesis Center (NESCent) Suite A200, W. Main Street 2024 Durham, NC 27705-4667 USA [email protected]

ISBN 978-94-007-1935-4 e-ISBN 978-94-007-1936-1 DOI 10.1007/978-94-007-1936-1 Springer Dordrecht Heidelberg London New York Library of Congress Control Number: 2011940207 © Springer Science+Business Media B.V. 2012 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)

Preface

Evolution is the chief architect behind a forest’s response to climate change and, as such, deserves a place in the professional education of those who manage natural resources. So this book’s aim is to introduce students and other future managers to the evolutionary dynamics of forests and to show how these models can guide what to plant under climate change. Such an ambitious task is made easier with a case study and I have chosen the Lost Pines of Texas. The Lost Pines forest has been an integral part of American forestry education for decades because it illustrates how forest managers can use ready-made natural variation for the benefit of tree planting programs. An updated version of this same idea is needed now because most of the Lost Pines forest was lost to wildfire on September 6, 2011. Determining what to plant now is a top priority because the Lost Pines case study has long held a value is disproportionately large for its small size and it behooves us to examine why this is so. Already at the drought-prone edge of the Pinus taeda range, the Lost Pines area is likely to be the first of this eastern species’ populations to experience the harsh effects of climate change. Put another way, the Lost Pines population is vulnerable enough to serve as a climate change bellwether and thus instructive about what to plant under climate change. But first we must understand what was once here. The Lost Pines area in central Texas is one of the best-documented places in North America. Human artifacts at nearby Buttermilk Creek1 date back as far as 15,000 year before present (B.P.). After these early arrivals came the Clovis people, other paleo-americans and then, in more recent times, Native Americans tribes. Incidence of fire probably rose as a consequence of these early humans. Here too were Spanish explorers who ventured forth more than three centuries ago and they were the first to document the Lost Pines area so this forest is a naturally occurring phenomenon. Geological records became available for the Lost Pines area with the discovery of lignite, oil, natural gas and aquifers which now supply 88 oil fields,

1

Waters M et al (2011) Science 331:1599–1603. v

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22 natural gas reservoirs and large reserves of lignitic coal.2 Extractive wealth from the Lost Pines area continues to contribute to the science-led Texas economy. This wealth was transformed into research universities, space exploration, biomedical facilities, computing and now alternative energy. Most of this innovation is centered in Texas cities and these cities have now expanded until they are side-by-side with scientifically precise agricultural systems. Within this radius of scientific achievement, the Lost Pines area in central Texas can lay another claim: here evolutionary principles were first applied to tree planting programs. This idea was so successful in restoring forests in Texas during some long drought-prone years that it became the gold standard for tree planting programs worldwide. Defined here as managed evolution, these principles were translated into quantitative and population genetics. The new field of tree improvement got its practical start here in the Lost Pines area, through the efforts of Dr. Bruce Zobel and others. Since then, many scientists including the author have continued to optimize the genetic quality of seedlings for the largest tree planting program in U.S. history and they did so by applying these same evolutionary principles. As with its past, the future value of the Lost Pines area now looms large. At first glance, the regional scale of the Lost Pines case study might seem inconsequential to the increasingly global science of forests but this is not so. Regional scales actually matter more than global or even continental scales3 when it comes to making future climate change meaningful. Regional forecasts are not yet available but they alone link scientific abstraction to the scales of societal meaning,4 not the other way around. No two regions will be affected by climate change in the same way and thus resource managers must know how a region’s conditions are likely to change, not only what global temperatures will be on average. Meanwhile, a place-centered inquiry5 can fill the gap and perhaps later complement regional forecasts. The Lost Pines case study is the right place-centered inquiry for Texas. Highly vulnerable to climate change,6 energy-producing Texas has less than 10% forest cover. This forest cover of the Lost Pines and elsewhere serves to slow climate change effects7 although, as seen from the 2011 wildfire, it will also be more prone to loss. How can these losses be staunched? There is no easy answer given the rapid urban population growth projected for central Texas. Slated for a population over 70 million in coming decades, urbanization tends to reduces forest cover. Other forces are at work too. Houston and other central Texas cities are particularly

2

Dutton et al (2006). Schiermeier Q (2010) Nature 463:284–287. 4 Jasanoff S (2010) Theory Cult Soc 27:233–253. 5 NRC (2010) Adapting the impacts of climate change. National Academies Press, Washington DC, 272 p. 6 Schmandt J, North G, Clarkson J (2011) The impact of global warming on Texas, 2nd edn. University of Texas Press, Austin, 318 p. 7 Turner et al (2009) Nature 462:278–279. 3

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vulnerable to forest cover loss because they border on a hurricane-prone part of the U.S. coastline, the Gulf of Mexico. Regional forecasts for central Texas are likely to be among the most complex and idiosyncratic but already they also point to a loss of forest cover. The Lost Pines case study is germane here too because it was one of the densely few forested areas in the prairie-savanna matrix of central Texas. Forest trees, including Pinus taeda, are largely undomesticated at this time and this opens the option of managing allelic richness, or genetic diversity, more explicitly for forest planting programs. Managing genetic diversity now has the added precision of genomics data. Genomics refers to large-scale DNA sequencing databases and these databases are available for Pinus taeda in the public domain. Federal science agencies have amply funded genetic diversity studies at the DNA sequencing level for this important timber species and now this knowledge can now be translated into better seedling planting stock. Identifying adaptive variation at the DNA sequence level and then making this explicit for consumer seedling choices has not yet happened. Doing so would be ideal for replanting the Pinus taeda forests of the Lost Pines area. Timber-growing for the United States has moved offshore and so now the U.S. forestry community must revise its societal pact. The community has fissured into two schools of thought: molecular domestication versus managed evolution. Molecular domestication, as the more prevalent view, advocates that Pinus taeda programs take concentrate on modifying wood properties for a few highly selected genotypes which can be clonally reproduced in limitless numbers. If so, then the rapid molecular domestication of Pinus taeda and other temperate species would follow a similar path as domestication of maize, soybeans or cotton. This molecular domestication portfolio for Pinus taeda includes not only use of genomics data but also the use of recombinant DNA technology, i.e. inserting transgenes or genetic engineering. Of particular interest here is genetic modification of wood quality. This portfolio has also led to a new industry, i.e. companies which sell only forest tree seedlings and these use a different business model from those timber companies which once grow seedlings for their own land. A few seedling-sales companies have expanded into global markets at the same time that many state-run nurseries are closing. Presently, forest managers in Texas can still purchase forest tree seedlings from either state-run nurseries or private seedling suppliers but this situation has already begun to change in favor of private sales. Managed evolution, as the other school of thought, takes the longer view that managing more genetic diversity explicitly is the better choice for temperate forestry and that forestry’s technology portfolio has already diverged from maize and other annual crops. A number of factors such as longevity have already put forestry on that separate path. By making more genetic diversity explicit, managed evolution can imbue forest tree seedlings with a genetic quality which hedges against climateinduced losses. I assert here that managed evolution is the better choice for U.S. forestry’s societal pact and that this should guide what to plant in the drought-prone Lost Pines area now. Managed evolution, as coupled with genomics, has not been endorsed by either multinational timber companies or private seedling sales companies.

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A synthesis of this book’s content. The Lost Pines case study draws on knowledge from many disciplines but even so there are still gaps and contradictions which require careful examination. A theory or model can be upturned easily with a new experiment, new records or new fossil finds. Theories and models are simply placeholders for more knowledge, not facts. Thus the reader is encouraged to follow the line of reasoning for a particular hypothesis throughout the book before deciding what additional knowledge is needed. The following hypotheses serve to thread discussion. Predicting how the U.S. South’s planted pine forests will fare under climate change uses ecological principles. These, along with economic forecasts, have generated optimistic forecasts for Pinus taeda as a species. We can agree that this is one species will not become extinct. However, these forecasts have yet to be downscaled to a regional level and it is here that local forest cover losses are prone to occur. Having anchored these models to the Lost Pines as a real-life ecosystem illustrates some guiding principles for managing forests under climate change. Evolutionary dynamics models for forests require a frame which is distinctly different from ecological forecasting. Here, the species is treated as an aggregate of populations and the population, not the species, becomes the unit of response. A population is composed of individuals and these individuals response via the entire life cycle. When seen through this life cycle lens, a forest ecosystem now takes on more than its usual terrestrial dimensions: it acquires aerial and perhaps aquatic dimensions because pollen and seed dispersal must be included in how a population responds to climate change. The population’s raw material for change resides with its genetic variation and forest trees have unusually high levels of genetic variation within and among populations. How this genetic variation is shaped by selection, gene flow, random drift and even mutation contributes to evolutionary dynamics models. Evolutionary dynamics models for forests are explicit yet rarely integrated into climate change forecasting or considered with the realm of forest policy solutions. One reason might be that they are based on forest tree populations that lived and died several thousands of years ago, during Quaternary glacial cycles. Most forest tree populations during the Quaternary responded to past climate change either dispersing seed colonies elsewhere (migration) or by death (extirpation) although few local stands did persist in place. Charting these Quaternary forest responses has been shown to be useful to contemporary problem-solving even though forest cover losses to global warming in the future are not fully analogous to those under glaciation. Evolutionary dynamics models, with more still emerging, swing between (i) forest trees as long-lived yet transient generalists prone to migration or (ii) a more stationary past which includes local adaptation. These frame a dichotomy which continues to move the discussion about evolutionary dynamics models forward. Other models include repeated hybridization and introgression with close relatives. Repeated hybridization followed by strong natural selection under abiotic stress can tip the balance in favor of local adaptation and these changes typically occur with human disturbance. How might these models be advanced to the point that they can guide decisions or contribute to policy solutions? Many have wrestled with this question and the

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best answer so far is to tie evolutionary dynamics models to ecological realism. Ecological realism, or anchoring to a real ecosystem, does nicely link evolutionary principles to forest management as shown here with disjunct Pinus taeda population in central Texas known as the Lost Pines. This choice is challenging because no Quaternary glaciation occurred within the Pinus taeda range and this is an aggressive early-successional colonizer which is synanthropic, or well-suited to human disturbance and to the extent that it readily colonizes near and around the built environments. In particular, this species and its close relatives seeds into open gaps cleared by fire or storms but ultimately its migratory pace of Pinus taeda has been hastened most of all by a human activity: tree planting. More human activity than tree planting has shaped the present-day Lost Pines ecosystem so that its present state cannot be assumed to resemble its past yet its past determines which evolutionary dynamics models fit best. The past of the Lost Pines area could be reconstructed by sifting through a large number of historical and geological records and these temporal records proved vital in re-thinking the Lost Pines case study. The Lost Pines forest was completely cutover by 1880 but its species composition may not have been purely Pinus taeda at that time. A close relative, Pinus echinata, was also documented to be here in the primary settlement forest and to a lesser extent, in the post-settlement, or secondary forest. Putative hybridization between the two has been well-documented. The Lost Pines ecosystem is more complex than a disjunct Pinus taeda population and this complexity bears on what evolutionary dynamics model fit and what to plant now. Similarly, Lost Pines population has been widely believed to be reproductively isolated from the rest of the Pinus taeda range but this is not absolutely supported either. Historical documents suggest that pine islands once connected the Lost Pines to the rest of its range as recently as the middle of the twentieth century and before that, the gap’s distance tended to fluctuate. To this I add the conjecture is that the pine archipelago in central Texas might have been lost with ebbing of the Little Ice Age, which occurred circa 1850 and that losses due to this minor climate shift could have coincided with the agricultural clearing during settlement. As a consequence of these two factors, climate and clearing, many pine stands in the larger pine archipelago of central Texas may have disappeared without return. Similarly, the range has shifted in east Texas too. Those vast Pinus taeda forests today can be traced to East Texas tree planting programs because in 1900, the original range of this species was confined to only a dozen counties. To this fluctuating distance, forest biology findings adds more doubt to the idea that the Lost Pines population is reproductively isolated: a distance of 100 km does not pose an insurmountable barrier for windborne transport of live pollen. Not having been tested dispersal for the Lost Pines population directly, this is posed here as a hypothesis: HYPOTHESIS: The Lost Pines population is reproductively connected to the rest of its species range in East Texas Piney Woods. Likewise, geological records challenge other widely-held assumptions about the Lost Pines ecosystem. Quaternary climate change, in a global sense, altered the course of Texas Gulf Coastal Plain rivers and these events carved out a highly fragmented set of niches for Pinus taeda in central Texas. The Lost Pines forest can

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grow on Pleistocene geological formations along the Colorado River and these formations coincide with gravelly soils. These Pleistocene geological formations alone do not provide scientific proof that this Pinus taeda population itself is a relictual forest. This claim requires fossil evidence. So far, the only fossil evidence comes from the Boriack Bog pine pollen fossil data. With some reluctance, many assert that this pine pollen fossil evidence is not compelling proof that Pinus taeda forests have persisted since the Pleistocene on certain geological formations along the Colorado River so this too is presented as a hypothesis. HYPOTHESIS: Some lineages in the Lost Pines population originated from Pleistocene relictual populations in central Texas. This ambiguity about fossil evidence limits which evolutionary dynamics model can be fit to the Lost Pines case study. Neither of the generalized models, either the retreating edge model or the stable rear edge model, provides an exact fit to the Lost Pines particulars. To see why, consider that ideally, fossil evidence would be combined with DNA-based evidence from living forest tree populations. Without this evidence, DNA-based population surveys can suggest but not prove a theory specific to the Lost Pines population. Such is the case for the local paleoclimate model which starts with the tacit assumption that the Lost Pines is a Pleistocene relictual population. Accordingly, the Lost Pines population has a DNA signature consistent with one or more massive contractions sometime during the Quaternary and our conjecture is that extremely hot dry climate of the late Holocene was so severe that the population shrunk, or severely contracted downward to very small number of trees. If so, the local paleoclimate model could explain the drought-tolerant attributes of the Lost Pines population.8 This is not without its shortcoming. Its fossil evidence is sparse which means its DNA-based evidence is spatially ambiguous and its statistical methods are not temporally exact, especially in case of a species with historically large populations. This is posed as another hypothesis: HYPOTHESIS: Some lineages in the Lost Pines population severely contracted during prolonged hot, dry conditions of the late Holocene and thus survived conditions more extreme than those present now. What can be said is that Pinus taeda requires a steady water source, as its common name of loblolly (or colloquially speaking, a hog wallow) implies. It is conjectural to state that the Lost Pines forest in the low-rainfall area of central Texas receives supplemental water from aquifer-fed springs and seeps in the Bastrop area but this assertion is an important one which deserves closer study. Closest to the surface in Bastrop County, the Wilcox-Carrizo aquifer beneath the Lost Pines is formed from the same Eocene geological events as its lignite reserves.

8

Al-Rabab’ah M (2003) Evolutionary dynamics of Pinus taeda L. in the late quaternary: an interdisciplinary approach. Texas A&M University, College Station, 264 p.

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These geologically-defined soils, often pocketed with seeps and springs, are thought to be among the few places that a pine stand could persist even if temperatures rose and water tables fell. HYPOTHESIS: Springs and seeps account for the persistence of the Lost Pines population in central Texas. If so, factoring these subterranean sources of water into the regional precipitation trends could improve the accuracy of bioclimate envelope (BCE) or aridity studies for Pinus taeda. These water sources, coupled with weathered Pleistocene soils, support one of the more original theories about the Lost Pines population which accompanied the local paleoclimate model so this too is presented as a hypothesis: HYPOTHESIS: The Lost Pines population is the source of western Pinus taeda population expansion at the end of the Holocene. That the Lost Pines population might have survived the Holocene so near the 100th meridian is hypothetical yet germane to gauging its chances of survival. Drought is likely to be worse in years to come and this will affect available water from the Colorado River. The Colorado River has highly vulnerable headwaters in the Southern Great Plains where future climate change effects will also be severe. Similarly, the Wilcox-Carrizo aquifer is slow to recharge thus there are concerns that this aquifer could be mined as cities around the Lost Pines area compete for this aquifer’s water. Springs and seeps could dry up. HYPOTHESIS: Scarcity of water will trigger large-scale losses to the Lost Pines forest planted now. While historical and geological records re-configured the Lost Pines case studies, this hypothesis points to what cannot be gained from applying evolutionary dynamics models. To wit, past death due to drought, fire or cyclones cannot be distinguished from death by other causes, i.e. pest and pathogen outbreaks. Also, managing genetic quality of a seedling can add resilience against abiotic stress for living trees but it offers no protection against catastrophic loss. In closing, managed evolution, or any model based on forest genetic composition, offers limited benefits. Such model assumes adequate genetic variation and that genetic variation itself cannot protect against wildfire or a declining water table. At best, it adds resilience when planting forests and that resilience can delay but not completely halt drought-imposed losses. Loss is the cohesive notion which winds through all evolutionary dynamics models. All future scenarios under climate change hold some measure of forest tree losses. Early losses begin when the population is stressed to its physiological limits at its home site and they progress until all individuals within this population have no more adaptive alleles within the reservoir of genetic variation. Short-term evolutionary processes do shape each population within its ecological context and this will continue to be the case for the Lost Pines population even after it is replanted. Pinus taeda planting programs, as the source of seeds, still have large reserves of genetic variation to draw upon but far too little is still known about its adaptive variation and that unknown is one of the wild cards for future forest management.

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In its simplest form, the Lost Pines case study illustrates how evolutionary principles can guide what to plant under future climate change. It does not focus on what is natural, what is rural or what elements set forests apart from human influence. Instead, the Lost Pines case study is presented from the start as a humandominated ecosystem. This coupled human-forest system is as dynamic as evolution itself and it is this odd entity that will dissemble under future climate change. To my thinking, future resource managers should incorporate evolutionary principles into planting programs but they also have a responsibility to explicitly manage against the expanding urban population’s drain on subterranean reserves of water and remain vigilant in retaining the right balance between forests and agriculture, recognizing that these are competing land uses at temperate latitudes. As for the recovery of the Lost Pines forest, nothing stays the same and there can be no return. Goethe said it best: “[Nature] is ever shaping new forms: what is, has never yet been; what has been, comes not again.”9 Managing the Lost Pines forests under climate change illustrates how a new pact between forestry and society can be forged and that the rubric of managed evolution is the right response under the rising uncertainty of climate change. Claire G. Williams

9

Quote from Johann Wolfgang von Goethe 1783 On Nature. From the translation by Huxley TH (1869) Nature 1:9.

Acknowledgements

Parts of this work have already been published in peer-reviewed scientific journals: American Journal of Botany, Molecular Ecology, Forest Ecology & Management, Heredity, Japanese Journal of Historical Botany, Nature Biotechnology, Canadian Journal of Forest Research and International Forestry Review. The book project started with two journal articles published with doctoral student Mohammad Al-Rabab’ah, now an associate professor at Jordan University of Science & Technology, and it took shape while working on an science diplomacy assignment in energy and environment at the U.S. State Department and finally came to a close at the University of Göttingen in Germany with a MWK travel grant from Lower Saxony. To my Texas colleagues: I am appreciative for your many contributions from start to finish. This project began science journalist Dick Stanley wrote about our research on the Lost Pines area in the Austin-American Statesman. His readers responded with useful commentary which led to archaeology, geology, aquifers and river terraces, the Houston toad, Clovis sites, Native Americans, bison, fire ecology, Goodrich Jones, and settler anecdotes. They took the time to write letters and email, to make phone calls, and to send invitations to meals, meetings, conferences and presentations. With their help, the Lost Pines forest took on a new interest which endured after departing my professorship at Texas A&M (1995–2004). This welcome was extended again a decade later: Professor Larry Gilbert at the University of Texas at Austin offered use of field research facilities and Professors Bonnie Jacob and David Meltzer and other colleagues at Southern Methodist vetted my formative ideas. Many thanks for this Texas welcome. To my North Carolina colleagues: I am equally appreciative to you for encouraging the completion of this project. In particular, I am indebted to Dr. Steve Anderson and the Forest History Society staff who provided resources and expertise. Likewise, the National Evolutionary Synthesis Center (NESCent) added in-kind support, library resources and expertise. The North Carolina State University’s D.H. Hill Library and its special collections provided access to the Bruce Zobel correspondence. Professor Peter White at the University of North Carolina’s Botanical Garden

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provided a public venue for this book in its latter stages. Truly, it takes a village to complete a book. Special thanks to Floyd Bridgwater for his many contributions, personal and professional, to this lengthy project. The two of us agree that this book should be dedicated to Professor Bruce Zobel (1920–2011) for many reasons. My appreciation also extends to many colleagues have supplied original research, expert advice, readings and lively discussions: these include Lisa Auckland, Robert Baker, Michael Blum, Robert Campbell, Fred Cubbage, Norma Fowler, Elizabeth Gillet, David Gwaze, Peter Kanowski, Gabriel Katul, Anna Kuparinen, Steve Jackson, James Lewis, William Lowe, Carol Lynn McCurdy, Victor Martinez, Corene Matyas, Cheryl Oakes, Andrea Piotti, Alan Pottinger, Elton Prewitt, William Platt, Humberto Reyes-Valdés, Megan Reynolds, Trina Roberts, Roy Plotnick, Ron Schmidtling, Philip Schoeneberger and Steve Vogel. Each of these experts provided compass bearings for this long search but I take sole responsibility for its synthesis. Claire G. Williams

Contents

Part I

Human Impacts on North American Forests

1

Climate Change ......................................................................................... 1.1 Introduction ...................................................................................... 1.2 Excess CO2 in the Atmosphere......................................................... 1.3 CO2 Integral to Life .......................................................................... 1.4 Not a Point-Source Pollutant ............................................................ 1.5 Long-Lived Molecule in the Earth’s Atmosphere ............................ 1.6 The Greenhouse Gas Effect .............................................................. 1.6.1 Other Greenhouse Gases ...................................................... 1.6.2 Measuring CO2 and CO2 Equivalents ................................... 1.7 More Than Greenhouse Gases ......................................................... 1.7.1 Climate Change Effects Are Regional ................................. 1.7.2 Hurricane Severity................................................................ 1.8 Loss of Forest Cover Accelerates Climate Change .......................... 1.9 Causes of Deforestation.................................................................... 1.10 U.S. South Forests ............................................................................ 1.11 Closing ............................................................................................ References and Related Readings ...............................................................

3 3 3 5 5 5 6 7 7 9 9 10 10 11 11 12 13

2

Predicting How Forests Will Respond .................................................... 2.1 Introduction ...................................................................................... 2.2 Pinus taeda Forests in the U.S. South .............................................. 2.3 Bioclimate Envelope (BCE) Models ................................................ 2.3.1 Lost Pines Anomaly ............................................................. 2.3.2 Predictions for U.S. Southern Pines ..................................... 2.3.3 Predictions for Pinus taeda in the U.S. South...................... 2.3.4 Predictions for Pinus taeda in Light of Seed Dispersal.................................................................. 2.3.5 Predictions for No-Analog Ecosystems ...............................

17 17 17 19 19 20 20 21 21

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2.4 2.5

Drawbacks to Bioclimate Envelope Predictions .............................. Evolutionary Dynamics Models ....................................................... 2.5.1 Population as the Unit of Response ..................................... 2.5.2 Genetic Variation as a Reservoir .......................................... 2.5.3 Measuring Genetic Variation................................................ 2.6 Past Climate Change Response ........................................................ 2.6.1 Local Persistence.................................................................. 2.6.2 Migration .............................................................................. 2.6.3 Extirpation ............................................................................ 2.7 The Role of Seed Dispersal .............................................................. 2.8 How Forest Respond ........................................................................ 2.9 Migration Rates ................................................................................ 2.10 Closing ............................................................................................. References and Related Readings ............................................................... Part II 3

22 23 23 23 23 24 24 24 26 26 27 27 27 28

The Lost Pines Narrative

A Forest Within a Prairie ......................................................................... 3.1 Introduction ...................................................................................... 3.2 The Lost Pines Area ......................................................................... 3.2.1 Bastrop State Park ................................................................ 3.2.2 Census Count ....................................................................... 3.2.3 The Lost Pines: Owners and Stakeholders ........................... 3.2.4 The Lost Pines: A Disjunct Population ................................ 3.2.5 Pinus taeda as Keystone Species ......................................... 3.2.6 Lost Pines:A Refugial Ecosystem ........................................ 3.3 Above Ground .................................................................................. 3.3.1 Low Rainfall and Prolonged Drought .................................. 3.3.2 Hurricanes, Tropical Storms and Ice .................................... 3.4 Beneath the Surface .......................................................................... 3.5 Regional Geography ......................................................................... 3.5.1 The Savanna-Prairie Matrix ................................................. 3.5.2 The Gap Between Lost Pines and Piney Woods .................. 3.6 Beyond the Matrix ............................................................................ 3.6.1 Austin and the Edwards Plateau ........................................... 3.6.2 San Antonio, Southern Texas Plains Mexico Border ........... 3.6.3 Coastal Plain and the Western Gulf Coast Basin Reference and Related Readings.......................................... 3.6.4 East to Houston, Piney Woods, and Louisiana Border ........ 3.6.5 North-Northeast to College Station, Dallas and Oklahoma Border .......................................................... 3.7 Closing ............................................................................................. References and Related Readings ...............................................................

35 35 35 36 40 41 43 44 44 45 45 45 47 48 48 49 50 50 51 51 52 52 52 54

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4

What Historical Records Add .................................................................. 4.1 Introduction ........................................................................................ 4.2 Early Human Activity in Texas .......................................................... 4.3 European Exploration ......................................................................... 4.3.1 New Spain .............................................................................. 4.3.2 Spain’s Military Road ............................................................ 4.3.3 Concerns Over the Louisiana Purchase.................................. 4.3.4 Moses Austin Petitions for a Land Grant ............................... 4.4 Settlement ........................................................................................... 4.4.1 New Spain and Mexico .......................................................... 4.4.2 The Republic of Texas............................................................ 4.4.3 The United States ................................................................... 4.4.4 The Confederate States of America ....................................... 4.4.5 Re-admitted to the United States ........................................... 4.4.6 Sargent’s Visit ........................................................................ 4.5 Managed Forests................................................................................. 4.5.1 Wasteful Logging Practices.................................................... 4.5.2 East Texas Piney Woods......................................................... 4.5.3 Early Reforestation................................................................. 4.5.4 Founding of the Texas Forest Service .................................... 4.5.5 Tree Improvement .................................................................. 4.5.6 A Role for the Lost Pines ....................................................... 4.5.7 Pine Islands in Central Texas ................................................. 4.5.8 Making Selections .................................................................. 4.6 Closing ............................................................................................... References and Related Readings ...............................................................

57 57 57 58 59 59 60 61 62 62 65 65 66 67 68 69 69 70 72 72 73 73 75 75 77 79

5

What Geological Records Add ................................................................ 5.1 Introduction ........................................................................................ 5.2 The Tale of Two Rivers ...................................................................... 5.2.1 The Colorado River of Texas ................................................. 5.2.2 The Brazos River .................................................................... 5.3 Geological Events............................................................................... 5.4 Wilcox-Carrizo Aquifer...................................................................... 5.4.1 The Lost Pines Forest and the Wilcox-Carrizo Aquifer ................................................................................... 5.5 Closing ............................................................................................... References and Related Readings ...............................................................

81 81 81 83 86 86 87

Part III 6

87 89 91

An Evolutionary Synthesis

Survivor of Past Climate Change Events ................................................ 97 6.1 Introduction ........................................................................................ 97 6.2 Taxonomic Classification ................................................................... 97

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6.3

Evolutionary Events ......................................................................... 6.3.1 Tertiary Period ........................................................................ 6.3.2 Quaternary Period .................................................................. 6.4 From Holocene Onward ................................................................... 6.5 Closing ............................................................................................. References and Related Readings .............................................................

98 98 100 107 107 108

7

The Pine Life Cycle ................................................................................. 7.1 Introduction ...................................................................................... 7.2 The Two Phases of the Life Cycle.................................................... 7.2.1 The Diploid Sporophyte Phase............................................... 7.2.2 The Haploid Gametophyte Phase ........................................... 7.3 Two Vehicles for Dispersal............................................................... 7.4 Pollen Dispersal................................................................................ 7.5 Seed Dispersal .................................................................................. 7.5.1 Colonization ........................................................................... 7.6 Evolutionary Consequences ............................................................. 7.6.1 Hybridization.......................................................................... 7.6.2 Serial Colonization ................................................................. 7.6.3 Sweepstakes Dispersal ........................................................... 7.6.4 Abiotic Stress Alters Seed Production ................................... 7.7 Closing ............................................................................................ References and Related Readings .............................................................

115 115 115 116 117 118 119 122 122 123 123 125 125 126 126 126

8

Short-term Evolutionary Processes ....................................................... 8.1 Introduction ...................................................................................... 8.2 Genetic Variation Protects ................................................................ 8.3 Forest Tree Populations Harbor High Genetic Diversity ................. 8.3.1 Gene Flow .............................................................................. 8.3.2 Locally Adapted Populations ................................................. 8.3.3 The Center-Periphery Model.................................................. 8.4 Evolutionary Models for Predicting Climate Change ...................... 8.4.1 Retreating Edge Model .......................................................... 8.4.2 Stable Rear Edge Model......................................................... 8.5 Evolutionary Dynamics Models: Experimental Findings ................ 8.5.1 Lost Pines: Retreating Edge or Stable Rear Edge? ................ 8.5.2 A Local Paleoclimate Model .................................................. 8.6 Closing ............................................................................................ References and Related Readings ............................................................

133 133 133 134 136 136 136 137 137 139 139 139 141 141 143

Contents

Part IV

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A First Approximation for the Future

9

Genetic Composition of the Planted Forest .......................................... 9.1 Introduction .................................................................................... 9.2 Forest Trees Are Largely Undomesticated ..................................... 9.2.1 Stage 1 Improved Seed Source......................................... 9.2.2 Stage 2 Early Domestication ............................................ 9.2.3 Stage 3 Semi-domestication ............................................. 9.3 Genetic Diversity as an Imperative ................................................ 9.4 Closing ........................................................................................... References and Related Readings .............................................................

151 151 152 153 153 154 155 156 157

10

Managing the Existing Forest ................................................................ 10.1 Introduction .................................................................................... 10.2 A First Approximation ................................................................... 10.2.1 A Scenario for Local Persistence ..................................... 10.2.2 A Scenario for Migration ................................................. 10.2.3 A Scenario for Extirpation ............................................... 10.2.4 Summarizing Scenarios.................................................... 10.3 Closing ........................................................................................... References and Related Readings .............................................................

159 159 159 160 161 162 163 164 167

Lexicon ............................................................................................................. 171 Index ................................................................................................................. 179

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Part I

Human Impacts on North American Forests

Michael Obersteiner (2009) Storing carbon in forests. Nature 458:151 Forests will take centuries to adapt to the disruptive processes that accompany climate change, making forest carbon stores vulnerable in the long term.

How might a forest fare over the next century under human-induced climate change? This driving question is addressed using a well-studied U.S. South species, Pinus taeda. This species and other pines have survived past climate change events over centuries, millennia and even millions of years so what is different about future climate change? Future climate change has no precedent. Rapid and abrupt, this type of climatechange has few signs of stabilizing over the next century. It is more complex than elevated levels of CO2 or global warming. Its complexity is greatest for temperate forests but regional forecasts are not yet available. Resource managers face a high degree of uncertainty about what type of forests to plant and how to best manage standing forests. Predictive models for future climate change are not yet scaled to regional effects at this time. Global circulation models show that climate change will be harsh at the westernmost edge of the Pinus taeda range, near the 100th meridian, and these models have been coupled with vegetation models to produce a number of large-scale forecasts. These forecasts show that, on the whole, U.S. South pine forests will migrate northward yet some parts of the Pinus taeda range have no forecasts and such is the case for the Lost Pines population at the westernmost edge of the species range. A finely-scaled dynamic model based on short-term evolutionary processes can serve as a complement to regional climate change forecasts and it can guide management practices. As shown by the Lost Pines narrative, a forest tree population and its life cycle together form the unit of response for future climate change.

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Chapter 1

Climate Change

1.1

Introduction

This chapter introduce how future climate change will affect forests and how forests in turn stabilize climate. This begins with a working definition for climate as weather data is collected over several decades or longer. Data are collected on synoptic meso-scale systems which shape wind direction, temperatures, precipitation patterns and for frequency of extreme events such as hurricanes or ice storms. Climate is a composite of statistical trends, both predicted and observed, and should not be confused with weather.

1.2

Excess CO2 in the Atmosphere

Atmospheric CO2 concentrations from the Industrial Revolution onwards have been rising sharply (Fig. 1.1; Stern 2006; IPCC 20071; Raupach et al. 2007). The world’s primary sources of industrial CO2 are coal-burning facilities although CO2 is also generated by naturally occurring sources such as volcanoes, earthquakes and deforestation. Industrial sources of CO2 are the primary problem and these have risen faster over the past two centuries2 than they have over the past 18,000 years

1 The IPCC is a committee of 2,500 scientists established in 1988 by the World Meteorological Organization and the United Nations Environmental Programme to provide objective assessment of human-induced climate change. 2 A disturbance is defined as a discrete event in time that causes abrupt change in an ecosystem. This means that a major change in climate within a 300-year interval over 10,000-year record qualifies as abrupt.

C.G. Williams, Evolutionary Dynamics of Forests under Climate Change, DOI 10.1007/978-94-007-1936-1_1, © Springer Science+Business Media B.V. 2012

3

4

1

Peak CO2 emissions must occur between 2000 –2015 This corresponds to a rise in global temperature 2.0 to 2.4 C -and to a rise in sea level 0.4 to 1.4 m Growth rate for global atmospheric CO2 for 2000-2006 was 1.93 ppm per year, highest since the start of the Mauna Loa continuous monitoring. Figures taken from IPPC Report November 2007 http://www.ipcc.ch/pdf/assessment-report/ar4

World CO2 emissions (GtCO2/yr)

140

Stabilization Scenario I: 450 ppm ceiling A pessimistic scenario

I :445-490 ppm CO2-eq II:490-535 ppm CO2-eq III:535-590 ppm CO2-eq IV:590-710 ppm CO2-eq V: 710-855 ppm CO2-eq VI:855-1130 ppm CO2-eq

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post-SRES range

60 40 20 0

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60 20

40 20

20 20

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120

Climate Change

10 8 VI 6

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0 GHG concentration stabilisation level (ppm CO2-eq)

Fig. 1.1 The target for atmospheric CO2 stabilization of 450 ppm ceiling is widely accepted although others, such as NASA scientist James Hansen asserts that this ceiling is considerably lower. This ceiling marks irreversible effects of global warming, i.e. melting of the polar ice caps, release of methane from clathrates, are predicted to occur if emissions exceed this ceiling. If so, peak CO2 emissions must occur before 2015. As shown here, this corresponds to a rise in global temperature 2.0–2.4°C and to a rise in sea level of 0.4–1.4 m. As of 2007, the growth rate for global atmospheric CO2 from 2000 to 2006 was 1.93 ppm per year, highest since the start of the Mauna Loa continuous monitoring (Source: IPPC Report November 2007 http://www.ipcc.ch/pdf/assessmentreport/ar4)

(Mannion 2006). Climate change records on geological time scales register no rise as steeply as this one. To understand how future climate change differs from past climate change,3 we must first understand more about its causal pollutant, CO2.

3 The mark of past climate change is omnipresent on the present-day landscape. To wit, presentday Texas was once part of the Western Inland Sea roughly 100 million years ago and this climate-induced event was instrumental in forming its oil, gas and coal reserves.

1.5 Long-Lived Molecule in the Earth’s Atmosphere

1.3

5

CO2 Integral to Life

Green plants including forest trees take up or sequester CO2 then give off oxygen O2 as part of photosynthesis, a process which converts sunlight into energy and thus sustains all life on earth (Mannion 2006). Tree growth is favored by elevated CO2 concentrations and faster tree growth means more carbon is sequestered in the shortterm (Luyssaert et al. 2007) but there are limits to how much CO2 can be taken up by forests.4 What CO2 is not sequestered by terrestrial ecosystems or by oceans becomes part of the excess of free floating CO2 molecules in the atmosphere. It is this execss CO2 acts as a pollutant and this pollutant has some novel characteristics.

1.4

Not a Point-Source Pollutant

The earth is sensitive only to its total CO2 burden. Excess CO2 concentration blankets the earth; it is not localized around its point sources. Unlike sulfur dioxide,5 CO2 concentrations are not localized, i.e. higher around its emission sources. This blanket of excess CO2 was first detected by continuously measuring the earth’s CO2 concentrations at a single location, the Mauna Loa station in Hawaii USA.6 This station, and other elsewhere, measured a rising CO2 excess which was not coming from Mauna Loa yet its steady rise could still be detected there (Keeling 2008). This provided the proof that the earth is indifferent – or agnostic – to the location of its point sources or even the type of CO2 emissions, coal burning or otherwise (Chameides and Oppenheimer 2007).

1.5

Long-Lived Molecule in the Earth’s Atmosphere

The other key feature is that CO2 molecules are long-lived. A molecule emitted today can persist for 50–100 years in the atmosphere. This means that CO2 emissions are measured not only as annual increase, or flux, but also in terms of a historical

4

Forests are not permanent. When they rot, die or burn, forest trees release, or emit, CO2 molecules. Point emissions of sulfur dioxide caused conifer forest dieback. 6 Rising CO2 inventory dates back to the 1950’s with continuous data from Mauna Loa, Hawaii USA providing the contentious yet convincing annual evidence that atmospheric CO2 concentrations were indeed rising. If CO2 had been measured only as often as surveys of the North Atlantic overturning circulation then it would have taken decades to obtain convincing evidence (Keeling 2008). 5

6

1

Climate Change

inventory7 (Raupach et al. 2007). In the atmosphere, carbon exists as its oxidized form, CO2 and as such, atmospheric CO2 is part of the global carbon cycle. The present atmospheric CO2 increase is composed of anthropogenic emissions of CO2 and a major source of CO2 emissions is the combustion of fossil fuels, mostly coalburning, although aluminum smeltering, some forms of glass-making and cement production also figure prominently.

1.6

The Greenhouse Gas Effect

Free-floating CO2 and the other greenhouse gases are harmful because of the greenhouse gas effect. In simplest terms, CO2 is relatively transparent to the visible light from the sun which heats the earth by day but CO2 is opaque to infrared light (heat) so at night it blocks the heat that the earth’s surface which would otherwise re-radiated back into space.8 Excess CO2 in the atmosphere is a heat-producing pollutant because it traps heat from the earth’s surface. If the earth was a perfectly smooth sphere then this rising CO2 concentrations in its atmosphere would spell global warming but that is not the case: the earth does not have a smooth surface. The amount of trapped heat is not uniform distributed so the greenhouse gas effect does not strictly translate into global warming. A more complex response is introduced by the earth’s irregular features such as its oceans, its mountain ranges, its polar ice caps and even its vast areas of forest. Forests in particular have a complex biophysical relationship to excess CO2 inventory; evapotranspiration, sunlight absorption and reflectivity all vary depending on latitude and forest type (Table 1.1; Canadell et al. 2007; Bonan 2008). This complexity means that no two regions will be affected in the same way by excess CO2 concentrations. Future climate change is regional, not global.

Table 1.1 Carbon is cycled between atmospheric, marine, land-based biota, ocean-based biota and mineral reservoirs Distribution of annual CO2 emissions 1970–1999 1990–1999 2000–2006 Atmosphere 0.44 0.39 0.45 Ocean 0.28 0.27 0.24 Land 0.28 0.34 0.3 The largest fluxes occur between the atmosphere and terrestrial biota such as forests. Shown here are the fractions of CO2 emissions absorbed by terrestrial ecosystems including forested ecosystems and by oceans is incomplete. The largest fraction of CO2 emissions (.45% or 45%) remains in the atmosphere over the time period of 2000–2006 (Adapted from Canadell et al. 2007)

7

From this point forward, units for carbon flux calculations can be useful: 1 teragram (TgC) equals 1 million metric tons carbon or 1 megaton (Mt), 1 petagram (PgC) equals 1 billion metric tons carbon. In English units, 1 lb carbon dioxide, measured as carbon units, equals 3.6667 pounds carbon. 8 Swedish scientist Svante Arrhenius won a Nobel Prize for this discovery of the greenhouse gas effect.

1.6

The Greenhouse Gas Effect

7

Table 1.2 Six classes of greenhouse gases are long-lived and tend to be evenly distributed throughout the earth’s atmosphere Greenhouse gas classes Global warming potential (100-year time horizon) 1 CO2 CH4 21 N2O 310 HFC class 140–11,700 CF4 class 6,500–9,200 SF6 class 23,900 Of these, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) account for the largest proportion: 83.1, 7.6. and 7.4% respectively and occur in the earth’s atmosphere whether or not humans are present. The other three classes are manmade industrial pollutants which are rare yet potent GHG: hydrofluorocarbons (HFC), perfluorocarbons (CF4) and sulfur fluoride (SF6)

1.6.1

Other Greenhouse Gases

Carbon dioxide is one of several greenhouse gases (Table 1.2). Among these six classes, CO2 is by far the most prevalent, accounting for 83.1% of all greenhouse gases (GHG). It is also less potent than the other five GHG classes. Methane and nitrous oxide are part of the earth’s atmosphere whether humans are present or not. The other three GHG classes are more potent. These are synthesized by humans, or “manmade”. To wit, sulfur hexafluoride (SF) gas is one of these synthetic greenhouse gases (Table 1.2). Emitted in trace amounts, SF has a global warming potential which is 23,000 times greater than CO2. Note too that CO2 and the other five classes are expressed as carbon dioxide equivalents, also abbreviated as CO2e (Table 1.2). Even if one accounts for CO2 and its GHG equivalents, there is more to future climate change.

1.6.2

Measuring CO2 and CO2 Equivalents

Timelines for the advance of human-induced climate change have been constructed using earth systems models. Earth systems, or global circulation models (GCM), show that CO2 emissions must be stabilized before reaching a ceiling of 450 ppm (IPCC 2007). This ceiling (Fig. 1.1) corresponds to a 50% probability of exceeding 2° warming from the greenhouse gas effect.9 This scenario has been widely accepted but now there is growing reason to think that this ceiling is too high. 9 This is only one of the IPCC scenarios. All are based on projections of possible future emissions and these can be grouped into four scenario families known as A1, A2, B1, and B2. These emphasize globalized vs. regionalized development on the A vs. B axis and economic growth vs. environmental stewardship on the 1 vs. 2 axis. Three variants of the A1 are globalized, economically oriented scenarios which lead to different emissions trajectories: A1FI refers to intensive dependence on fossil fuels, A1T refers to alternative technology largely replaces fossil fuels, and A1B refers to balanced energy supply between fossil fuels and alternatives.

8

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Climate Change

2100 Greenhouse gas effect Excess CO2 Long-lived molecular half-life Soot, aerosols, pollutants

2040

Zone of rising uncertainty

2010

Fig. 1.2 A concept map for future climate change as forecast by Shell Energy Scenarios to 2050 (p. 40). Forests, whether standing or yet to be planted, will only stabilize or mitigate climate change if they are resilient and healthy. Climate adaptation for forests draws on evolutionary dynamics models

The ceiling measures excess CO2 and CO2e concentrations which will trigger irreversible changes. Included here is the melting of polar ice caps. Melting ice caps will cause a volatilization of methane-rich clathrates beneath the polar ice cap. Methane, or CH4, is a more potent greenhouse gas than CO2 (Table 1.2) so release of large-scale methane would register as an irreversible tipping point to the CO2 and CO2e balance for the earth’s atmosphere. To prevent this point of no return then CO2 emissions must peak soon. This cutoff date is the basis for the oft-cited statement that the world needs 60–80% reductions over 1990 emissions by 2050 but many other variables come into play: human population increase, energy consumption, forest cover losses and the accuracy of earth systems models. Now, in the year 2011, it is not clear what that path towards lower emissions will look like. Future climate change, as a largely regional problem without precedent, brings a rising uncertainty (Fig. 1.2). Consider that the growth rate for global atmospheric CO2 concentrations for 2000–2006 was 1.93 ppm per year, the highest since the start of continuous monitoring at Mauna Loa. This signals that we have entered a period of unusually sharp CO2 increases. Since 2004, global atmospheric carbon dioxide levels have risen from 280 to 377 ppmv (Stern 2006; Raupach et al. 2007) so now CO2 levels are already so high that even if industrial CO2 emissions halted today, the ecological consequences of long-lived excess CO2 concentrations blanketing the earth will continue unabated for centuries. Irreversible future climate change will already be manifest between years 2050 and 2100 (Fig. 1.1; IPCC 2007). This will occur first near the 100th meridian in North America. Western North America’s temperatures are predicted to rise 3.5–4°C

1.7

More Than Greenhouse Gases

9

under the assumption of moderate CO2 emissions scenarios (IPCC 2007; Cole 2009). Future climate change effects are already measurable within the continental United States (Parmesan 2006) and hence we have entered the zone of uncertainty (Fig. 1.2).

1.7

More Than Greenhouse Gases

CO2 and its equivalents will be accompanied by other pollutants and among these will be ozone precursors, volatile organic compounds, and black carbon (i.e. Kopp and Mauzerall 2010). All of these factors contribute not only to the complexity of human-induced climate change but also to a rising uncertainty about whether forests can thrive (Bonan 2008).

1.7.1

Climate Change Effects Are Regional

Human-induced climate change is rapid, more complex than elevated CO2 and global warming and it is regionally variable. Each region will experience its own customized plethora of climate change effects.10 Rain and snow are expected to fall in fewer, more intense events and these same events will also bring flooding or even prolonged dry periods (Parmesan 2007). While total precipitation might increase globally, some regions will be drier while others will receive more rain or snow than usual. Higher surface temperatures favor higher wind speeds, or turbulence. Greater surface drying from higher wind speeds in turn leads to more frequent thunderstorms. Thunderstorms are expected to bring heavier rains and higher wind speeds than usual. Future climate change brings several sources of uncertainty. Models for temperate forests bring the greatest uncertainty (Jackson 2008). The carbon uptake and release, or carbon budgets, are well-known but less is known about regional biophysical effects affecting climate. Other unknowns include how small-scale forests will fare (Loarie et al. 2009). One of the most critical questions is how forests influence precipitation.11 Removing forest cover in Brazil’s Amazon rainforests alters spring rains in Iowa by way of a phenomenon known as teleconnection (Avissar and Werth 2005). Similarly, how aquifers and other groundwater systems will be altered by climate change is not yet known either. Hurricane severity is expected to increase

10 Regional-scale effects of climate change for human-dominated have yet to be addressed in detail (Schiermeier 2010). 11 Forests and human activities within forests together influence climate. Forests can mitigate climate change but how these can be integrated for forest policy is stunningly complex, especially for the purpose of regional forecasting.

10

1

Climate Change

but it is still debatable as to whether hurricane frequency will rise. Human-induced climate change holds a high degree of uncertainty for North America’s humandominated temperate latitudes.

1.7.2

Hurricane Severity

Of particular interest to North Americans is the hurricane-prone Gulf of Mexico. Hurricanes damage forests in the southern U.S. to such an extent that the damaged forests abruptly shift from a sink for CO2 uptake to a source of CO2 emissions (Chambers et al. 2007; Zeng et al. 2009). Consider that Hurricane Katrina in the Gulf of Mexico damaged 320 million forest trees (Chambers et al. 2007). Only 15% of destroyed timber could be salvaged so large quantities of woody debris was left behind. This debris attracted bark beetles, other detrimental insects and fungal diseases and these attacked both dead and live trees (Lugo 2008). Still more losses came from drying woody debris which served as fodder for forest fires. If ignited, the burning debris torches live trees (Chambers et al. 2007; Galik and Jackson 2009). Amplified by climate change, more severe hurricanes could bring dire consequences for the U.S. South’s richly timbered regions.

1.8

Loss of Forest Cover Accelerates Climate Change

More than 75% of the earth’s surface has now been modified by human activity over the past three centuries (Ellis and Ramankutty 2008) and forest cover loss figures prominently among this myriad of land use changes. Halting forest cover loss was chronic for decades until now, when deforestation is now recognized as a major contributor to greenhouse gas emissions (Table 1.1; Canadell et al. 2007). Fossil fuel emissions are clearly the culprit but deforestation too has added steeply to the rise of CO2 concentrations too. Slowing deforestation is a complex problem.12 Roughly 31% of the earth’s surface, or 4 billion ha, is now covered in forests (Goodale et al. 2002; Bonan 2008; FAO-FRA 2010). About 13 million ha of forest cover is being lost annually with losses are concentrated in the tropical regions of the Americas, Asia and Africa (Canadell et al. 2007). Not only forest deforestation but also forest degradation is hastening forest cover losses13 (Chazdon 2008). 12 The relationship between forest and climate change is highly interactive. These interactions have continental or even global ramifications (Avissar and Werth 2005). Strictly speaking, forests do not respond to climate change. 13 Forest trees offset anthropogenic carbon dioxide (CO2) emissions by removing CO2 molecules from the atmosphere via photosynthesis and converting it to wood. By slowing deforestation, forest policy can prevent CO2 molecules from entering the atmosphere.

1.10

1.9

U.S. South Forests

11

Causes of Deforestation

Amazon deforestation, now lessening (FAO-FRA 2010),14 can be traced to nation-building for one of the world’s fastest growing economies, Brazil. Here, forests are cleared for industrial-scale agricultural operations and for farm-to-market highways through these new agricultural corridors (Fearnside 2007). By contrast, the Congo Basin forest cover is increasingly lost to shifting food cultivation, human population increases, logging, and military conflict (Makana and Thomas 2006). Indonesia has had long-lasting peat fires which consume vast areas of its forests, adding further to atmospheric CO2 burden (Page et al. 2002). Most of the world’s forests are government-owned (Agrawal et al. 2008) and these provide a revenue stream during a financial downturn when there is little else to draw upon except the sale of logs and logging concessions. Related to this downturn are illegal logging profits and these too siphon off tropical forest cover. Forest cover losses worldwide are huge next to tree planting. Of the 4 billion ha of the world’s forest cover, only 187 million ha (5%) is planted forest and of this, only 72 million ha are managed for industrial wood (Cubbage et al. 2005). An even smaller fraction, about 25 million ha worldwide, is now classified as intensively managed planted forests (or IMPF)15 (Kanowski and Murray 2008). Deforestation is rapid within the borders of some equatorial countries now but its root causes are global. Losing forest cover loss is linked by global trade too. Strong market demand comes from the U.S. and other affluent developed countries, to losses due to exotic forest pathogens and pests spread by global trade and to widespread industrialization and urbanization which contributes to stifling atmospheric pollutants, soot and particulate matter. Globalization of trade takes its toll on forest cover too.

1.10

U.S. South Forests

This area, inclusive of the Lost Pines, covers nearly 216 million ha in 13 states. This is only 24% of the land area of the United States but it represents 60% of this country’s forests16 (Wear 2002). It too has had a history of rapid forest cover loss as part of nation-building. These are secondary forests, mostly planted on what was once agricultural clearings and cutover timber. Its forest cover has declined by 49% since

14

FAO-FRA. 2010. Global Forest Resource Assessment. FAO Forestry Paper. Rome. http://foris.fao.org/. 15 Intensively managed planted forests (IMPF) refer to many types of landholdings and a wide range of sizes. The largest of these (>10,000 ha) are held by companies, governments or even public-private partnerships. At the other end of the scale are independent landowners and even small growers (