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Simulating Vegetation Migration in Response to Climate Change in a Dynamic Vegetation-Climate Model Simulating Vegetation Migration in Response to Climate Change in a Dynamic Vegetation-Climate Model by Rebecca Shira Snell A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Faculty of Forestry University of Toronto © Copyright by Rebecca Shira Snell 2013 Simulating Vegetation Migration in Response to Climate Change in a Dynamic Vegetation-Climate Model Rebecca Shira Snell Doctor of Philosophy Faculty of Forestry University of Toronto 2013 Abstract A central issue in climate change research is to identify what species will be most affected by variations in temperature, precipitation or CO 2 and via which underlying mechanisms. Dynamic global vegetation models (DGVMs) have been used to address questions of habitat shifts, extinctions and changes in carbon and nutrient cycling. However, DGVMs have been criticized for assuming full migration and using the most generic of plant functional types (PFTs) to describe vegetation cover. My doctoral research addresses both of these concerns. In the first study, I added two new tropical PFTs to an existing regional model (LPJ-GUESS) to improve vegetation representation in Central America. Although there was an improvement in the representation of some biomes such as the pine-oak forests, LPJ-GUESS was still unable to capture the distribution of arid ecosystems. The model representations of fire, soil, and processes unique to desert vegetation are discussed as possible explanations. The remaining three chapters deal with the assumption of full migration, where plants can arrive at any location regardless of distance or physical barriers. Using LPJ-GUESS, I imposed migration limitations by using fat- tailed seed dispersal kernels. I used three temperate tree species with different life history strategies to test the new dispersal functionality. Simulated migration rates for Acer rubrum (141 m year -1) and Pinus rigida (76 m year -1) correspond well to pollen and genetic reconstructed ii rates. However, migration rates for Tsuga canadensis (85 m year -1) were considerably slower than historical rates. A sensitivity analysis showed that maturation age is the most important parameter for determining rates of spread, but it is the dispersal kernel which determines if there is any long distance dispersal or not. The final study demonstrates how northerly refugia populations could have impacted landscape recolonization following the retreat of the last glacier. Using three species with known refugia ( Acer rubrum , Fagus grandifolia , Picea glauca ), colonization rates were faster with a northerly refugia population present. The number of refugia locations also had a positive effect on landscape recolonization rates, which was most pronounced when populations were separated. The results from this thesis illustrate the improvements made in vegetation-climate models, giving us increasing confidence in the quality of future climate change predictions. iii Acknowledgments I would like to thank my supervisor, Dr. Sharon Cowling, for providing me with both professional and personal support over the years. Dr. Cowling allowed me the freedom to pursue my interests, yet was always there to share her advice and enthusiasm. I have the utmost respect for Dr. Cowling as a scientist and as a person, and to be able to say that at the end of a Ph.D. is something I am grateful for! I would also like to extend my appreciation to Dr. Brad Bass (University of Toronto and Environment Canada), Dr. Sarah Finkelstein (University of Toronto) and Dr. Marie-Josée Fortin (University of Toronto) for their time on my supervisory committee and for their excellent research advice over the years. I would also like to acknowledge my internal and external examination members, Dr. Sean Thomas (University of Toronto) and Dr. Stephen Sitch (University of Exeter) for their constructive comments on the final version of my thesis. My Ph.D. thesis is based upon an existing model, LPJ-GUESS. I would like to thank Dr. Ben Smith (Lund University) for permitting me to use his model which allowed me to accomplish my goals. I would also like to thank Dr. Jing Chen (University of Toronto) and Bruce Huang for access to the Unix cluster in PGB. Thank you to the entire Cowling lab, and everyone who ever shared PG201B with me. Your companionship, conversation and many, many coffee breaks helped to make my graduate experience an enjoyable one! On a personal note, I would like to thank all my friends and family who have supported me throughout my graduate experience. I could always count on your love, encouragement and emergency babysitting. I would also like to thank my father for suggesting a Latin Hypercube sampling design for Chapter 4. Who knew there was so much in common between plant ecology and nuclear physics! To my husband, Jason. I can only say thank you and know that it is not enough. iv Table of Contents Acknowledgments.......................................................................................................................... iv Table of Contents............................................................................................................................ v List of Tables .................................................................................................................................. x List of Figures............................................................................................................................... xii List of Appendices ........................................................................................................................ xv Chapter 1......................................................................................................................................... 1 1 Introduction................................................................................................................................ 1 1.1 Seed dispersal and vegetation migration............................................................................. 2 1.2 Vegetation-climate models ................................................................................................. 2 1.2.1 Species distribution models .................................................................................... 2 1.2.2 Dynamic global vegetation models......................................................................... 3 1.3 Dispersal in vegetation-climate models.............................................................................. 4 1.3.1 Species distribution models .................................................................................... 4 1.3.2 Dynamic global vegetation models......................................................................... 5 1.4 Adding dispersal into a DGVM .......................................................................................... 6 1.4.1 Challenges to simulating dispersal in DGVMs....................................................... 6 1.4.2 The model, LPJ-GUESS ......................................................................................... 7 1.5 Outline of chapters and objectives...................................................................................... 9 1.6 Glossary of terms .............................................................................................................. 11 1.7 References......................................................................................................................... 16 Chapter 2....................................................................................................................................... 20 2 Simulating regional vegetation-climate dynamics for Central America: tropical versus temperate applications.............................................................................................................. 20 2.1 Abstract............................................................................................................................. 20 2.2 Introduction....................................................................................................................... 20 v 2.3 Methods............................................................................................................................. 22 2.3.1 Description of LPJ-GUESS .................................................................................. 22 2.3.2 PFT parameterizations .......................................................................................... 23 2.3.3 Modelling protocol................................................................................................ 24 2.3.4 Model evaluation from biome comparison........................................................... 25 2.3.5 Model evaluation from remote sensing data......................................................... 26 2.4 Results............................................................................................................................... 26 2.4.1 Biome comparison with Olson map...................................................................... 26 2.4.2 Biome comparison with Haxeltine & Prentice map ............................................. 27 2.4.3 MODIS comparison.............................................................................................. 28 2.5 Discussion......................................................................................................................... 28 2.6 References........................................................................................................................
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