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The Effects of Human Trampling Disturbance, Plant-Plant Interactions, and Climate on the Performance and Distribution of The THE EFFECTS OF HUMAN TRAMPLING DISTURBANCE, PLANT-PLANT INTERACTIONS, AND CLIMATE ON THE PERFORMANCE AND DISTRIBUTION OF THE ALPINE CUSHION PLANT SILENE ACAULIS by NATHALIE ISABELLE CHARDON B.A., University of California, Berkeley, 2010 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirement for the degree of Doctor of Philosophy Environmental Studies Program 2018 ii This thesis entitled: The Effects of Human Trampling Disturbance, Plant-Plant Interactions, and Climate on the Performance and Distribution of the Alpine Cushion Plant Silene acaulis written by Nathalie Isabelle Chardon has been approved for the Environmental Studies Program ________________________________ Prof. Daniel F. Doak (Chair) ________________________________ Prof. William D. Bowman ________________________________ Prof. Katherine N. Suding ________________________________ Dr. Sonja Wipf ________________________________ Dr. Christian Rixen Date: _______________ The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above-mentioned discipline. iii Chardon, N. I. (Ph.D., Environmental Studies) The Effects of Human Trampling Disturbance, Plant-Plant Interactions, and Climate on the Performance and Distribution of the Alpine Cushion Plant Silene acaulis Thesis directed by Prof. Daniel F. Doak Delineating the abiotic and biotic processes that set species geographic distributions has been a central theme in ecological research for hundreds of years, yet we still do not understand many aspects of this broad question. Discerning what processes determine past and current range limits is particularly critical for predicting how species distributions will respond to climate change. In Chapters 2 and 3, I address how the interactions of climate, inter-species interactions such as competition, and human disturbances together influence range limits. I show that disturbance has positive effects on the alpine cushion plants Silene acaulis and Minuartia obtusiloba at the species’ lower elevational range limits, likely through a reduction in competitive interactions. In contrast, at upper elevational range limits, where biotic interactions are minimal, disturbance exerts neutral or negative effects. However, disturbance has negative effects at the S. acaulis population level, as evidenced by a reduction in population density and reproductive indices. While facilitation by cushion plants is thought to increase with abiotic stress, it is also left unanswered if disturbance influences these facilitative effects. I show that disturbance does not alter plant-plant interactions, and that, in fact, competitive interactions prevail in S. acaulis communities. In Chapter 4, I address a second major issue in the understanding and prediction of range limits by examining if local populations respond differently to climatic drivers limiting their distribution. By constructing Species Distribution Models (SDMs) based on S. acaulis’ global distribution and separately with subpopulations based on genetic and habitat differences, I show that potential local population adaptation to climate renders a iv global SDM inaccurate. Furthermore, the manner in which subpopulations are defined greatly affects habitat suitability predictions, which are poorly linked to measures of S. acaulis population performance and facilitative interaction strength. The final aspect of my work is outlined in Chapter 5, for which I developed a citizen science application for smart phones to aid in the identification and hence appreciation of alpine plants in the Colorado Rocky Mountains. Altogether, my work illustrates the need to carefully examine all factors important in both setting species range limits and determining distribution shifts. v DEDICATION To the mountains, which always bring me home. * * * There is an intimate sense of calm that descends over the dusky valleys, the rolling alpine fields, and the bright snowy peaks with the alpine sunset. It is a peace found only here, away from nocturnal electricity, confining walls of civilization, and expectations of society. Here is where sitting on a stone wall listening to the alpine cowbells is the main attraction for the evening. The simplicity of drinking tea to a valley waking up with dew on its leaves and hiking through the morning light is how we sharpen our senses for the day. Coming back to an alpine hut after a long day at altitude, cooking to such a mesmerizing sunset, and swapping stories about where life has taken us is how we bid farewell to a beautiful day. These bare essentials are forgotten, buried behind layers of fast-paced living, when alpine days are too far and few in between. This is what we lose in the circus, our inner balance with the big around us. 7 July 2016 Calanda Hut, Switzerland * * * vi ACKNOWLEDGMENTS Dan Doak, for your patience, wisdom, and guidance to turn me into a scientist Doak Lab, for being my “Alice in Wonderland” family Committee Members, for guiding me with countless discussions and advice Team Mountain Ecosystems, for welcoming me year after year Samuel Pironon, for your constant modeling advice and ideas Field Assistants, for hiking thousands of vertical feet to collect data My Asolos, for taking every step with me Carol Wessman, for tea and influential discussions on disturbance David Ackerly, for lighting in me a passion for research and species range limits Elizabeth Bergstrom, for encouraging my love of alpine ecology 3821 Paseo del Prado, for dogs and conversations about all things science Alain Chardon, for always fighting on my side Elisabeth Chardon, for knowing I could succeed Alessandra Chardon, for keeping me sane with your understanding Florence Chardon, for your excitement in my path and emergency proof-reading Christian Lauber, for your commitment, humor, and countless air miles Katherine Lawry, for soggy talks about a decision and Lawry’s Editing Services Friends, for romping around with me in mountains, canyons, and deserts My skis and climbing harness, for letting me play and reminding me to do so Funding generously provided by: CU Boulder Environmental Studies Program, Zeno Karl Schindler Foundation, Santa Barbara Scholarship Foundation, CU Boulder Graduate School, American Alpine Club, Indian Peaks Wilderness Alliance, John Marr Ecology Fund, CU Herbarium Hazel Schmoll Fellowship, Swiss Botanical Society vii CONTENTS CHAPTER 1. Introduction ………………………………………………………………… 1 1.1. Range Limits and Climate Change …..…………………………… 1 1.2. Local Disturbance and Range Limits ………..…………………… 3 1.3. Alpine Plant Interactions …….……………..……………………… 5 1.4. Predicting Range Shifts ...…….……………..……………………… 6 1.5. Disturbance Impacts ………………….……..……………………… 7 1.6. Species Distribution Models …..…………………………………… 8 2. Disturbance benefits two alpine cushion plants at lower, but not upper, elevational range limits …………………………...………...… 9 2.1. Abstract …………………………...…………………………………… 9 2.2. Introduction ………………………………...………………………… 10 2.3. Materials & Methods ……………………...………………………… 15 2.3.1. Sites ………………………….……...……………….………… 15 2.3.2. Study species …………………………...……………….……. 17 2.3.3. Data collection …………………………...……………….…... 18 2.3.4. Statistical analyses …………………………...……………… 20 2.4. Results …………………………...……………….…………………… 22 2.5. Discussion …………………………...……………….……………….. 30 viii 2.6. Acknowledgments …………………………...……………….……… 34 2.7. Data Accessibility …………………………...……………….………. 34 2.8. Author Contributions ……………………...……………….……….. 35 3. Local trampling disturbance effects on alpine plant populations and communities: Negative implications for climate change vulnerability …………………………………………………...………...… 36 3.1. Abstract ………………………...…………...……………….……….. 36 3.2. Introduction …………………...…………...……………….……….. 37 3.3. Materials & Methods ……………………..……………….……….. 44 3.3.1. Sites ……..……………...…………...……………….……….. 44 3.3.2. Field measurements: cushion plants …………………….. 45 3.3.3. Field measurements: community effects and species interactions ………………………...……….……….……….. 47 3.3.4. Statistical analyses: cushion plants ………….….……….. 48 3.3.5. Statistical analyses: community effects ……..….……….. 50 3.3.6. Statistical analyses: species interactions ……..……..….. 52 3.4. Results ……………………………………………………….……….. 53 3.4.1. Cushion plants ……………………..……………….……….. 53 3.4.2. Community effects: inside species ……………….……….. 58 3.4.3. Community effects: neighboring species …………..…….. 62 3.4.4. Species interactions ………………….…………….……….. 64 3.5. Discussion ………….……………………………………….……….. 65 ix 3.5.1. Cushion plants ………….………………………….………… 65 3.5.2. Community effects and species interactions ….…….…… 67 3.6. Acknowledgments ………………………………..………..………… 73 3.7. Data Accessibility ……………………….…………………………… 74 3.8. Author Contributions ……………………...……………...………… 74 4. Subpopulation species distribution models outperform global model for an arctic-alpine plant …………………………….………... 75 4.1. Abstract …..………………………………………………….………... 75 4.2. Introduction ..……………………………………………….………… 76 4.3. Methods …………………………………………..………….………... 85 4.3.1. Climate data ……………………………..………….……….. 85 4.3.2. Species occurrences ……………………..………….……….. 85 4.3.3. Species traits ……………..……………..………….……….. 87 4.3.4. SDMs ……………………………………..………….……….. 89 4.3.5. Analyses ……………………..………………..…….……….. 91 4.4. Results ……………………………………………………….……….. 94 4.5. Discussion ………………………………………..………….……….. 104 4.6. Acknowledgments ………………..……………..………….……….. 110 4.7. Data Accessibility ……………..………………..………….……….
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