Vegetation and the Terrestrial Carbon Cycle Modelling the First 400 Million

Cambridge University Press 0521801966 - Vegetation and the Terrestrial Carbon Cycle: Modelling the First 400 Million Years D. J. Beerling and F. I. Woodward Frontmatter More information

Vegetation and the terrestrial carbon cycle Modelling the ﬁrst 400 million years

Plants have colonised and modiﬁed the World’s surface for the last 400 million years. In this book the authors demonstrate that an understanding of the role of vegetation in the terrestrial carbon cycle during this time can be gained by linking the key mechanistic elements of present day vegetation processes to models of the global climate during different geological eras. The resulting simulations of climate and vegetation processes tie in with observable geological data, such as the distributions of coals and evaporites, supporting the validity of the authors’ approach. Simulation of possible conditions in future centuries are also presented, providing valuable predictions of the status of the earth’s vegetation and carbon cycle at a time of global warming.

David Beerling is a Royal Society University Research Fellow and Honorary Reader in the Department of Animal and Plant Sciences at the University of Shefﬁeld. He is holder of a 2001 Philip Leverhulme Prize for his work in the earth sciences.

Ian Woodward is Professor of Plant Ecology in the Department of Animal and Plant Sciences at the University of Shefﬁeld. He is author of Climate and Plant Distribution (1987) and co-editor of Plant Functional Types (1997).

© Cambridge University Press www.cambridge.org Cambridge University Press 0521801966 - Vegetation and the Terrestrial Carbon Cycle: Modelling the First 400 Million Years D. J. Beerling and F. I. Woodward Frontmatter More information

Vegetation and the terrestrial carbon cycle: Modelling the ﬁrst 400 million years

D.J. Beerling & F.I. Woodward Department of Animal and Plant Sciences, University of Shefﬁeld, Shefﬁeld S10 2TN, U.K.

published by the press syndicate of the university of cambridge The Pitt Building, Trumpington Street, Cambridge, United Kingdom

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First published 2001

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Library of Congress Cataloguing in Publication data

Beerling, D. J. Vegetation and the terrestrial carbon cycle : modelling the first 400 million years / D.J. Beerling & F.I. Woodward. p. cm. Includes bibliographical references (p. ). `ISBN 0 521 80196 6 1. Carbon cycle (Biogeochemistry)–Mathematical models. 2. Plant ecology–Mathematical models. 3. Paleoclimatology–Mathematical models. I. Woodward, F.I. II. Title. QH344. B43 2001 577Ј.144Ј015118–dc21

ISBN 0 521 80196 6 hardback

Contents

Preface vii Acknowledgements ix

1 Introduction 1 2 Investigating the past from the present 9 3 Climate and terrestrial vegetation 23 4 Climate and terrestrial vegetation of the present 53 5 The late Carboniferous 100 6 The Jurassic 135 7 The Cretaceous 183 8 The Eocene 238 9 The Quaternary 280 10 Climate and terrestrial vegetation in the future 340 11 Endview 353

References 361 Index 395

Preface

The study of plant distributions is a continuous feature of ecology. These studies may range from a small area of ground to the whole of the terrestrial biosphere. The information from such studies underpins our current understanding of the terrestrial biosphere. Unfortunately this information, on its own, is not sufﬁcient to answer large questions, such as what controls the current distribution of plants, or how will the current distribution and behaviour of plants respond to global environmental change? These are important questions and ones which are presented increasingly in order to satisfy human knowledge and decision making. Indeed the question, put to ecologists in the 1980s, of how will terrestrial vegetation respond to global warming could not be answered then and only now, 20 years later, is there some hope that we understand some of the major mechanisms involved and their likely outcomes. There is also no doubt that such questions are good for the development of ecology, in contrast to likely serious consequences for mankind. A feature of long-term studies in ecology is that there is nothing really new, most things have happened before, if only we could have seen them. There is current concern over the rapid increase in atmospheric CO™ concentrations but in geological times the atmospheric CO™ concentrations, and the Earth’s tem- perature have frequently been higher than the present. No doubt plants and vegetation will respond and adapt to future change, however mankind requires a more improbable outcome, that nothing should change, even though atmospheric composition and climate are changing rapidly. An outcome as likely as that expected from the actions of Svein Forkbeard’s son. A more serious question is how much will vegetation change and how much will ecosystem services change, such as water supply, the provision of biomass and the capacity of the biosphere to sequester anthropogenic releases of CO™.These are difﬁcult questions to answer and any approach which makes predictions

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viii Preface

must have mechanistic underpinning to have any chance of approaching reality. One approach taken in the area of climate change research has been to make predictions back in time, when the environment was different from the present. Predictions can then be made and tested against data collected at the appropriate time. Previous warm periods, such as 6000 years before present, have been a favourite for investigation and have proved useful for testing models developed for the contemporary world. A problem in going further back in time to geological eras is that the information about the climate and the biosphere is much more limited. However the relatively recent application of general circulation models to simulating past climates has provided a useful source of past climatic data. These GCM runs are constrained by proxy estimates of ocean temperatures and are probably reasonable estimates of past climates, although there are limited opportunities for testing their validity. The value of these simulations is that their data can be used to drive vegetation models and the outputs of the vegetation models can be compared with fossil data which have not been used to constrain the GCMs. This approach of looking at past vegetation behaviour, and the carbon cycle in particular, is a new endeavour which implies a number of critical features. In particular it assumes that the contemporary understanding of the carbon cycle applies equally well at any other time. It also assumes that associated processes, for instance the water cycle and vegetation processes, such as succes- sion and responses to climate and atmospheric CO™ have also operated in essentially the same manner as the present. The fact that photosynthesis drives vegetation processes suggests that contemporary understanding will have geological relevance. This book describes approaches to testing quantita- tively how much this relevance amounts to and how we can deal with uncer- tainty in both vegetation and climate models. It is axiomatic that models are wrong, the question is how wrong and how much does this matter. These features will be tested for a wide range of eras before ﬁnally modelling the responses of vegetation to one particular scenario of future climatic change. Not all eras during the life of terrestrial vegetation have been covered, because GCMs are not currently available but those which have been completed have been periods when vegetation has been challenged by a wide variety of unusual conditions. Our ﬁnal hope is that we can show a range of responses by vegetation and the carbon cycle which stimulate further interest and enquiry, before our predictions of the future become the predictions of the present.

D.J. Beerling F.I. Woodward

Acknowledgements

Numerous scientiﬁc friends and colleagues gave generously of their time and hard-won data during the course of writing this book. In particular, we are indebted to Paul Valdes (University of Reading) for providing the global palaeoclimatic datasets from the Universities Global Atmospheric Modelling Programme (UGAMP) which constitute the core portion of the global simulations presented here, and Bette Otto-Bliesner (National Center for Atmospheric Research, Boulder, Colorado) and Gary Upchurch (Southwest Texas State University, Texas) for providing the global climatic simulation of the latest Cretaceous used in Chapter 7 as the basis for our analysis of the effects of the Cretaceous–Tertiary boundary impact event. This book would not have been possible without Mark Lomas whose mathematical, program- ming and mapping skills apparently know no bounds. Bill Chaloner provided much unwitting encouragement over the past three years and brought an even greater amount of sanity to bear on some of our wilder excursions, and we are both extremely grateful for his input. Jayne Young is thanked for the arduous task of diligently checking and pointing up errors in citations and the reference list throughout the entire text. For critically reviewing and commenting upon various parts of the text, and in some cases unselﬁshly providing unpublished data, we thank (in alpha- betical order): Pat Behling, Richard Betts, Bill Chaloner, Chris Cleal, Geoff Creber, Jane Francis, Colin Osborne, Andrew Scott, Paul Valdes, Paul Wignall and Jack Williams. Various discussions along the way with Bob Berner, Bill Emanuel, Jane Francis, Tim Lenton, Barry Lomax, Martin Heimann, Colin Osborne, Paul Quick, Hank Shugart, Andrew Watson and Gary Upchurch further helped shape our ideas on different parts of the text. Any remaining errors are, of course, our own responsibility. DJB gratefully acknowledges funding through a Royal Society University Fellowship and, for some of the research reported here, through grants from

x Acknowledgements

the Natural Environment Research Council, the European Commission and the Leverhulme Trust. FIW gratefully acknowledges support from the Natural Environment Research Council and the European Commission. Finally, we thank our families and friends for providing that all-important quality rest and relaxation time. DJB thanks Mum & Malcolm, Dad & Sue, Julie & Simon (& little Sophie), and Juliette for love and support. I also thank the many friends who have put up with me during the various stages of writing of this book especially Colin, Jarrod, Dan, Simon, Maria, Liz, Phil, Vicky, Charlotte, Helen, Steve and Mark A. FIW thanks Pearl, Helen and David and his wood-turning lathe for unpredictable but enjoyable pointers to another life.