Harvesting native seed to supply landscape-scale restoration: evaluating risks and sustainable practices A DISSERTATION SUBMITTED TO THE FACULTY OF THE UNIVERSITY OF MINNESOTA BY Justin Carl Meissen IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Dr. Susan M. Galatowitsch, Dr. Meredith W. Cornett June 2016 © Justin Carl Meissen 2016 ACKNOWLEDGEMENTS This research was made possible by funds provided by a National Science Foundation Integrative Graduate Education and Research Traineeship in Risk Analysis for Introduced Species and Genotypes, the Lessard-Sams Outdoor Heritage Fund, The Nature Conservancy Nebraska Chapter's J.E. Weaver Competitive Grants Program, The Nature Conservancy in Minnesota, North Dakota, and South Dakota, and The Dayton Fund of the Bell Museum of Natural History. Travel funds used to present this research at several international conferences were made possible by the Conservation Biology Program’s Travel Grant Award. I am tremendously grateful to my advisors Dr. Meredith Cornett and Dr. Susan Galatowitsch, who lent their enduring support, guidance, and knowledge throughout my time at the University of Minnesota. They were both instrumental in helping me develop the skills and ideas necessary to be a good conservation scientist. I also thank my thesis committee who were all essential to developing my research capabilities. Dr. Joseph Fargione gave me exceptional advice on many aspects of my research, especially on study design and data analysis. Dr. Robert Haight was integral in helping me develop sound demographic models, and he provided helpful analytical advice throughout this research. Dr. Anthony D’Amato helped me develop the early stages of my research and always offered useful perspectives on fruitful directions for research. Many people helped make this research possible by lending logistical support. I give special thanks to native seed harvesters Adam Teiken, Jeff Straub, Mike Ratzlaff, and Garth Kaste for providing access to private study sites and valuable insight into seed harvest history and practice in Minnesota. I also thank numerous members of the natural resources community in Minnesota who assisted me in finding seed harvest and land management histories of prairies: Brian Winter, Russ Reisz, Christine Reisz, Ross Hier, Larry Hanson, and Blane Klemek. Rhett Johnson imparted outstanding insight on prairie ecology and plant identification. Matt Mecklenburg was instrumental in carrying out prescribed fires in my seed harvest experiment, helped plant seedlings, and provided the equipment used for experimental treatments. Travis Issendorf assisted in implementing the seed harvest experiment. Neal Feeken supported me in developing research questions i that were relevant to land managers. Aaron Rendahl contributed sound advice to the statistical analysis of several aspects of my research. Roger Meissner and Pam Warnke helped ensure the success of my greenhouse research. Many thanks are also merited by my field and greenhouse assistants Jake VanderYacht, Sabin Adams, and Jenny Heck. I thank my fellow members of the Galatowitsch lab, who made the time working on this dissertation a fun and enriching experience. In particular, I give many thanks to Julia Bohnen who helped me throughout the course of this research in many ways in the field, the lab, and especially in the greenhouse. Laura Phillips-Mao assisted me with developing demographic models and was especially helpful in providing guidance with modeling software. Katherine Swanson aided me in carrying out experiment treatments and collecting data. Finally, I thank my parents Patty and Carl Meissen, who have given me love and support throughout my life. They imparted to me the underlying persistence and resourcefulness needed to undertake, carry out, and successfully complete my degree. ii ABSTRACT Seed supply limits large-scale restorations, which often rely on seed collection from remnant ecosystems. Overharvesting seed may deplete populations, exacerbate seed limitation, and jeopardize ecosystem integrity, but these risks have not been formally studied. Many life history traits are linked to species’ reliance on seed reproduction, and so may provide a useful framework to address seed harvest risks. I evaluated whether life history traits predict susceptibility to overharvest by comparing tallgrass prairies in Minnesota (USA) harvested at varying frequencies (every year, once per 3-5 years, unharvested). I identified species less likely to occur on frequently harvested sites then tested whether lifespan, clonality and seed production predicted harvest sensitivity. Short-lived, non-clonal species were sensitive to seed harvest while long-lived clonal species were not, suggesting that life history traits provide a means to predict seed harvest risk. To verify the predictive utility of life history traits and determine extinction risks from seed harvest over long restoration timeframes (25 years), I used matrix models of clonal Solidago canadensis and Anemone canadensis and non-clonal Rudbeckia hirta, Packera aureus, Zizia aurea, and Liatris ligulistylis to simulate seed harvest and extinction risk. I simulated 5 scenarios: no harvest; annual harvest at 50%/75% intensity; and triennial harvest at 50%/75% intensity. Non-clonal species were insensitive to triennial and 50% harvest, but susceptible to extinction risks of up to 92% with annual 75% harvest. Clonal species were insensitive to all harvest scenarios. To maintain populations of non-clonal species in the long- term, high intensity annual harvest should be avoided. To demonstrate the risk of overharvest in short-lived, non-clonal species and determine sustainable harvest regimes, I conducted a field experiment varying seed harvest intensity (0, 50%, or 100% seed removed) and management (burned or unburned) for R. hirta populations. I compared seedling recruitment and seed production among treatments, and found that seed production nearly doubled with burning. Moderate intensity harvest with burning allowed high levels of seedling recruitment, but high harvest intensity prevented recruitment, as predicted for a short-lived, non-clonal species. A regime combining moderate intensity harvest with fire management provides seeds while also conserving at-risk seed donor sources. iii TABLE OF CONTENTS LIST OF TABLES .............................................................................................................. v LIST OF FIGURES ........................................................................................................... vi GENERAL INTRODUCTION ........................................................................................... 1 CHAPTER 1 ....................................................................................................................... 5 CHAPTER 2 ..................................................................................................................... 20 CHAPTER 3 ..................................................................................................................... 39 GENERAL CONCLUSION ............................................................................................. 54 BIBLIOGRAPHY ............................................................................................................. 80 iv LIST OF TABLES Table 1.1. Environmental variables controlled for during site selection. ......................... 57 Table 1.2. Prescribed burn history of sites compared in this study. ................................. 58 Table 1.3. Attributes, measures, and data sources of three life history traits tested in determining plant species response to seed harvest. ......................................................... 59 Table 1.4. Summary of species occurrence ...................................................................... 60 Table 2.1. Study species, life history, and literature sources supporting model construction. ...................................................................................................................... 62 Table 2.2. Maximum annual seed harvest rates preventing population declines (λ< 1) or elevated extinction risk (ER=0.05) ................................................................................... 63 v LIST OF FIGURES Figure 1.1. Locations of 17 study sites in northwestern Minnesota. ................................ 64 Figure 1.2. Two dimensional NMDS ordination of species found in prairies wild- harvested for seed ............................................................................................................. 65 Figure 1.3. Mean species richness (± standard error) per m2 in unharvested, infrequently harvested and frequently harvested prairies ...................................................................... 66 Figure 1.4. Examples of tallgrass prairies harvested for seed over 11 years .................... 67 Figure 2.1. Study species life cycle diagrams. .................................................................. 68 Figure 2.2. Stage-based transition probabilities ................................................................ 69 Figure 2.3. Extinction risk (± 95% confidence interval) for model species populations under 5 seed harvest scenarios. ......................................................................................... 71 Figure 2.4. Seed harvest scenario output for non-clonal species ...................................... 72 Figure 2.5. Seed harvest scenario output for clonal