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Modeling the Spatial Distribution of Invasive Plant Species on Southeast Farallon Island

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Modeling the Spatial Distribution of Invasive Plant Species on Southeast Farallon Island MODELING THE SPATIAL DISTRIBUTION OF INVASIVE PLANT SPECIES ON SOUTHEAST FARALLON ISLAND A Thesis submitted to the faculty of /\5> San Francisco State University In partial fulfillment of the requirements for o?0 4 the Degree ( a E Q & * . (^3'? Master of Arts In Geography by Quentin James Clark San Francisco, California August 2017 Copyright by Quentin Janies Clark 2017 CERTIFICATION OF APPROVAL I certify that I have read Modeling the Spatial Distribution of Invasive Plant Species on Southeast Farallon Island by Quentin James Clark, and that in my opinion this work meets the criteria for approving a thesis submitted in partial fulfillment of the requirement for the degree Master of Arts in Geography at San Francisco State University. Barbara A. Holzman, Pl£D. Professor Emerita Professor MODELING THE SPATIAL DISTRIBUTION OF INVASIVE PLANT SPECIES ON SOUTHEAST FARALLON ISLAND Quentin James Clark San Francisco, California 2017 This project analyzes the spatial distribution of seven invasive plant species on Southeast Farallon Island, California using a generalized additive model (GAM). Species selected for modeling are Chenopodium murale (nettle-leaved goosefoot), Ehrharta erecta (panic veldt grass), Plantago coronopus (cut-leaf plantain), Tetragonia tetragonioides (New Zealand spinach), an annual grasses group, a Malva spp. (mallow) group, and Sonchus spp. (sowthistle) group. Models identify patterns and causal factors in the distribution of targeted species, as well as detect locations within the study area that are vulnerable to future colonization. Results reveal that elevation, surface slope, surface aspect, topographic position, human activity, and proximity to pinniped haul-out locations have the greatest influence on the predicted distributions of targeted species. Furthermore, distribution maps identify multiple locations on the island that are vulnerable to invasions by one or more target species. I certify that the AbstractAbstract is a correct representation of the content of this thesis.thesis. Date ACKNOWLEDGEMENTS Foremost, I would like to thank Dr. Barbara A. Holzman, my committee chair, for her willingness to work with me on this project and her unwavering support throughout the entire process. Thank you to Dr. Ellen Hines for her guidance, patience, and endless positivity. Many thanks to Gerard McChesney and Jonathan Shore of the U.S. Fish and Wildlife Service; Russell Bradley, Pete Warzybok, and Ryan Berger of Point Blue Conservation Science; and Richard Chasey, Kerstin Kalchmayr, Lauren Scheinberg, Jeff Blumenthal, Sara Fiori, Rob Thoms, Aiko Weverka, Darren Blackburn, and Anna Studwell of San Francisco State University. Funding for this work was partly provided by a grant from USFWS (#F15PX02325), the College of Science and Engineering, and the Department of Geography & Environment. Lastly, I would like to thank my partner, Francesca MacCormack, who is my inspiration and guiding light, and my parents, Dan and Gretchen, who instilled in me my love of geography and exploration at a young age. v TABLE OF CONTENTS List of Tables...........................................................................................................................vii List of Figures........................................................................................................................ viii List of Appendices................................................................................................................... ix Introduction.................................................................................................................................1 Project Objective........................................................................................................... 6 Methods......................................................................................................................................8 Study Area.....................................................................................................................8 Field Data.....................................................................................................................10 Environmental Predictor Variables............................................................................18 Analysis and Modeling...............................................................................................25 Results...................................................................................................................................... 29 Discussion................................................................................................................................ 38 Environmental Predictor Variables and Predicted Distributions............................39 Overall Model Performance.......................................................................................48 Management Implications.......................................................................................... 51 Limitations of Data.....................................................................................................53 Conclusion...............................................................................................................................55 References 57 LIST OF TABLES Table Page 1. Species selected for modeling..............................................................................7 2. Environmental predictor variables....................................................................19 3. Presence cells for each targeted species...........................................................25 4. Predicted presence cells for each targeted species............................................ 30 5. Variables selected for model training...............................................................30 6. Variable influence on predicted distributions.................................................. 31 7. Assessment of model performance...................................................................31 vii LIST OF FIGURES Figures Page 1. Map of Southeast Farallon Island......................................................................71 2. Results from 2016 invasive plant inventory.....................................................72 3. Distribution of Chenopodium murale on SEFI in 2016..................................73 4. Distribution of Ehrharta erecta on SEFI in 2016............................................74 5. Distribution of Plantago coronopus on SEFI in 2016.................................... 75 6. Distribution of Tetragonia tetragonioides on SEFI in 2016............................76 7. Distribution of annual grasses on SEFI in 2016..............................................77 8. Distribution of Malva spp. on SEFI in 2016....................................................78 9. Distribution of Sonchus spp. on SEFI in 2016.................................................79 10. 10A-D Maps of elevation, surface slope, and transformed aspect................. 80 11. 11A-D Maps of solar radiation, TPI, TCI, and soil depth...............................81 12. 12A-C Maps of distance to trails & structures, seabirds, and pinnipeds 82 13. Predicted distribution of target species combined........................................... 83 14. Predicted distribution of Chenopodium murale................................................84 15. Predicted distribution of Ehrharta erecta......................................................... 85 16. Predicted distribution of Plantago coronopus..................................................86 17. Predicted distribution of Tetragonia tetragonioides........................................ 87 18. Predicted distribution of annual grasses........................................................... 88 19. Predicted distribution of Malva spp...................................................................89 20. Predicted distribution of Sonchus spp................................................................90 / LIST OF APPENDICES Appendix Page A. ANOVA Test Results.............................................. ..91 B. Descriptive Statistics for Predicted Presence Cells ..94 ix 1 Introduction The dispersion of plant species beyond the boundaries of their evolutionary origins is a global phenomenon with significant ecological consequences. On oceanic islands, the effects of invasive non-native plant species are particularly acute. Invasive plants can significantly alter the processes and functionality of island ecosystems, as well as have a negative influence on the distribution and abundance of native flora and fauna (Meyer & Lavergne 2004). Impacts are magnified on islands due to vulnerabilities such as geographic isolation, limited terrestrial size, high levels of endemism, and low biodiversity (Castro et al. 2007). The introduction of invasive plant species is considered one of the greatest threats to the continued survival of native, often endemic, flora and fauna on oceanic islands around the world (Vitousek 2002). On Southeast Farallon Island (SEFI), located 48 kilometers west of San Francisco, California (Figure 1), invasive plant species have an impact on the ecological makeup of the island. The presence of invasive plant species is a concern for the U.S. Fish and Wildlife Service (USFWS), which manages the island, due to the influence these species have on the Island’s native species (USFWS 2009). Invasive plant species on SEFI displace native vegetation and eliminate viable habitat for native plant species (USFWS 2009).
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