University of New Hampshire University of New Hampshire Scholars' Repository Master's Theses and Capstones Student Scholarship Summer 2018 Abundance data change geographic estimates of terrestrial invasive plant risk in the contiguous United States Mitchell W. O'Neill University of New Hampshire, Durham Follow this and additional works at: https://scholars.unh.edu/thesis Recommended Citation O'Neill, Mitchell W., "Abundance data change geographic estimates of terrestrial invasive plant risk in the contiguous United States" (2018). Master's Theses and Capstones. 1207. https://scholars.unh.edu/thesis/1207 This Thesis is brought to you for free and open access by the Student Scholarship at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Master's Theses and Capstones by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. ABUNDANCE DATA CHANGE GEOGRAPHIC ESTIMATES OF TERRESTRIAL PLANT INVASION RISK IN THE CONTIGUOUS UNITED STATES BY MITCHELL W. O’NEILL Bachelor of Arts, Biology & Studio Art, University of Vermont, 2015 THESIS Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Master of Science in Natural Resources: Environmental Conservation September, 2018 i ALL RIGHTS RESERVED © 2018 Mitchell W. O’Neill ii This thesis has been examined and approved in partial fulfillment of the requirements for the degree of Master of Science in Natural Resources: Environmental Conservation by: Thesis Director, Dr. Jenica M. Allen, Assistant Professor, Natural Resources & the Environment Dr. Thomas D. Lee, Associate Professor, Natural Resources & the Environment Dr. Rebecca J. Rowe, Associate Professor, Natural Resources & the Environment On May 22, 2018 Original approval signatures are on file with the University of New Hampshire Graduate School. iii ACKNOWLEDGEMENTS First, I’d like to thank my advisor, Dr. Jenica Allen, for supporting and challenging me as a budding scientist. I will forever appreciate being treated as an intellectual equal when I clearly have a lot to learn, and for your endless dedication to my success as a graduate student as well as my professional development. Working with you has been a pleasure. I would also like to thank my committee members Dr. Rebecca Rowe and Dr. Thomas Lee for their support of my graduate career and valuable insights on my thesis work. In addition, I thank Tom for his mentorship during my first semester here at UNH as his TA. I thank Dr. Bethany Bradley at the University of Massachusetts for her insights on my project from its conception to its completion. I also thank Rebekah Wallace, the EDDMapS Data coordinator for sending us a full download of the database that allowed for the research in this document, and for her help in interpreting the abundance data. Thank you to the Allen Lab (Dr. Jenica Allen, Dr. Tim Szewczyk, Katie Moran, and Ceara Sweetser) for the interesting and informative discussions on invasive plants and the regular feedback on my research progress. I specifically thank Ceara for numerous data processing contributions to this project, and Tim for his advice on the final edits of this thesis and his help with various technical struggles. I also thank my parents, without whom I would never have gotten to this point where I have the privilege of pursuing what fascinates me. Last but not least, I thank my girlfriend, Tori, for joining me in New Hampshire so that I could pursue my interests and for supporting and inspiring me every single day. This project was funded by the National Science Foundation (BCS Award # 1560925). iv TABLE OF CONTENTS COPYRIGHT PAGE ………………………………………………………………. ii COMMITTEE PAGE ………………………………………………………………. iii ACKNOWLEGEMENTS …………………………………………………………... iv LIST OF FIGURES ……………………………………………………………….... vii LIST OF TABLES ………………………………………………………………….. vii ABSTRACT ………………………………………………………………………… viii CHAPTER PAGE I. Invasive plant impacts, management, and biogeography……………………. 1 Why are invasive plants important? ……………………………………….. 1 Strategies for managing invasive plants .…………………………………... 3 Invasive plant biogeography …...………………………………….............. 4 Summary ……………………………………………………………........... 7 II. Abundance data change geographic estimates of terrestrial invasive plant risk in the contiguous United States…………………….……………………. 8 Introduction ………………………………………………………………... 8 Methods ……………………………………………………………………. 12 Study region ………………………………………………………... 12 Invasive species data ………………………………………………. 13 Environmental data ………………………………………………... 16 Species Distribution Modeling …………………………………...... 17 Species-level abundance assessments ……………………………… 20 v Hotspot comparison ………………………………………………... 22 Results ……………………………………………………………………… 23 Model quality and species retained ………………………………... 23 Establishment and impact ranges………………….……………….. 26 Invasive species hotspots …………………………………………... 29 Discussion ………………………………………………………………….. 32 Conclusion ………………………………………………………………….. 37 LIST OF REFERENCES …………………………………………………………... 39 APPENDIX A: Ecoregions and land cover in the contiguous United States .……… 48 APPENDIX B: Invasive species data in the United States …………………………. 50 APPENDIX C: Ordinal ranking and data cleaning for multiple abundance metrics .. 54 APPENDIX D: Abundance-based species distribution modeling using infested area 60 APPENDIX E: Intermediate model results …………..…………............................... 64 vi LIST OF FIGURES FIGURES PAGE 1. Visualization of the modeling process for an example species ....……................... 21 2. Composition of species traits for 1,045 terrestrial invasive plants, 155 species with sufficient abundance data, and 70 species that passed through all three model screenings….….…………………………………………..……………... 25 3. Histogram of Cohen’s kappas for the best fit ordinal regressions for the 70 species included in the analysis ……………………………………………….... 26 4. Histograms of potential establishment range size, potential impact range size, and percent infilling………………..………………………………………………... 27 5. The relationship between range size and sample size and between establishment range size and impact range size……………………………………....………... 28 6. Invasive species richness and abundance hotspots overlaid and the proportion of high-abundance species………………………………………...………..……... 30 7. Ecoregion composition of the contiguous U.S., potential invasive species richness hotspots, and abundance hotspots .………………................................ 31 A1. Level I ecoregions in the contiguous U.S. ……….......……………………….... 48 A2. Geographic distribution of absence records ..…………………………………... 50 A3. Spatial bias surface from modeling sampling effort as a response to road and human population density across the contiguous U.S. …..………………......... 50 A4. Box plot illustrating the congruency between infested area and text data ……... 59 A5. Map of potential species richness and the potential number of species at high abundance …………………………………………………………………….... 70 LIST OF TABLES TABLES PAGE 1. Summary of the combination of several abundance metrics into an ordinal abundance ranking scheme .……………………………………..……………… 15 2. Summary of sequential model screening ..………………………………............... 24 A1. Area and percent of the contiguous U.S. belonging to each ecoregion and land cover class ….....…............................................................................................... 49 A2. Aggregation and selection of proportional land cover classes ……...………….. 49 A3. Invasive plant list sources for each state in the contiguous U.S. ……………….. 51 A4. Invasive species abundance data availability by abundance metric …..………... 54 A5. Pairwise correlations between all abundance metrics ………………………….. 60 A6. Summary of model results for all 155 species with adequate data …………….. 64 vii ABSTRACT ABUNDANCE DATA CHANGE GEOGRAPHIC ESTIMATES OF TERRESTRIAL PLANT INVASION RISK IN THE CONTIGUOUS UNITED STATES by Mitchell W. O’Neill University of New Hampshire, September, 2018 Invasive plants pose severe threats to ecosystems worldwide. Geographic invasion risk is often assessed using occurrence-based species distribution modeling, which estimates where species can occur but cannot represent variation in abundance, a crucial component of impact. I assembled an ordinal abundance dataset for 155 terrestrial invasive plant species in the contiguous United States based on reports to the Early Detection & Distribution Mapping System, a georeferenced invasive species data repository. I used maximum entropy models to estimate range boundaries and ordinal regression to estimate abundance within ranges. I predicted the areas where establishment is possible (potential establishment ranges), and where high abundance is likely (potential impact ranges) for each species, and compared where many species may establish (richness hotspots) to areas where many species may achieve high abundance (abundance hotspots). The potential impact range encompasses a small portion of the potential establishment range for many species (median: 9%). High abundance populations have not yet been observed across much of potential impact ranges for each species, indicating substantial risk for expansion. Forty-seven percent of the richness hotspots were overlapped by the abundance hotspots. Eastern Temperate Forests constituted large portions of both hotspots viii (80% of richness hotspots, 49% of abundance hotspots), but abundance hotspots included large areas not identified