Page intentionally left blank AN ABSTRACT OF THE THESIS OF Scott Richard Mitchell for the degree of Master of Science in Wildlife Science presented on March 5, 2020 Title: Impacts of Range Management Decisions on Native Pollinators: Innovative Grazing Practices and Riparian Restoration Abstract approved: ______________________________________________________ Sandra J. DeBano Abstract Animal pollination is critical to plant reproduction in agricultural and wildland ecosystems. Much of the production of seeds and fruits in natural areas, which underlie many food webs, depends on pollination services by insects. The taxon responsible for delivering the bulk of these services in most temperate systems is bees. While colony collapse disorder in the nonnative European honey bee (Apis mellifera) is a significant concern and one that has generated much media and scientific interest, recent studies have indicated that native, unmanaged bees may be declining as well. To increase the likelihood of continued delivery of pollination services, land managers need to have a comprehensive understanding of how management actions may affect native bees. One dominant land type, especially in the Pacific Northwest of the United States (US), is rangelands. Rangelands are known to support diverse pollinator communities and face land management challenges such as multiple-use and historic degradation. My thesis examines how one potentially important stressor, livestock grazing, affects native bee and plant communities and how shrubs used in the restoration of riparian areas common in rangelands can provide resources to a diverse community of native bees. My first chapter provides a general introduction to the topic of native pollinators and a broad overview of the importance of pollinators, their basic habitat and biological needs, and some of the stressors that may be affecting populations. The purpose of this chapter is to provide context and background knowledge for the chapters that follow. Chapter two focuses on one potentially important stressor of native bee communities in the American West – livestock grazing. In this chapter, I examine the effects of, late-season, moderate intensity, rotational cattle grazing on native bees and the blooming plants they depend on. To understand the effects of grazing on bee and plant communities, we conducted bee and blooming plant surveys at 28 sites located at two eastern Oregon study locations in the summer of 2018. One of the locations was a riparian wet-meadow system and the other was a bunchgrass prairie system. At each location, half of the sites were grazed by cattle at some point in the summer and half were not. Bee and plant communities at both locations varied through the growing season, with peaks in species richness and diversity occurring early to mid- season. We found location specific effects of cattle grazing on bee and blooming plant communities. At the riparian meadow location, we found that cattle grazing had short-term effects in reducing bloom abundance, species richness, and Shannon diversity in July and August, but these effects did not translate to any significant effects on bee communities. At the bunchgrass prairie location, we found no significant short-term effects of grazing on blooming plant communities and no negative effects on native bees. In fact, we detected higher bee abundance and richness in grazed sites at this location. An analysis of longer term-grazing at the second location revealed no detectable effect of grazing on blooming plant or native bee communities. Chapter three focuses on the interactions of native bees and flowering plants in a restored riparian area. To understand how bees interact with flowering plants, we conducted extensive hand-net surveys of bees in 2018 and 2019 from April to September in the restored area. To understand the changes in blooming plant community richness throughout the season, we conducted plant richness surveys throughout the 2018 growing season. We found a diverse community of bees that interacted with a diverse community of blooming plants. Early in the season (April), we found that blooming forbs were significantly more abundant and species rich than blooming shrubs. While forbs were more abundant in the early-season, we found no evidence that bees foraged on forbs at a higher rate than shrubs. Willow seemed to be important in supporting several apparent specialist bee foragers in the early-season. Later in the season, both shrubs and forbs remained important resources for bees, and we found bees that were apparent specialists on both shrub and forb blooms. Chapter four summarizes the key findings of the previous two chapters and provides some basic recommendations for land management with objectives related to pollinator health. I also make some suggestions for future research directions that could build on the findings described in this thesis. Collectively, the results of this thesis provide hope for pollinator conservation in inland Pacific Northwest grasslands. The second chapter indicates that late-season, rotational, cattle grazing may help mitigate some of the negative effects of cattle grazing on native bees that have been observed in some systems. The third chapter indicates that riparian restoration activities, especially planting blooming shrubs, may provide important forage resources for native bees in Pacific Northwest rangelands. ©Copyright by Scott Richard Mitchell March 5, 2020 All Rights Reserved Impacts of Range Management Decisions on Native Pollinators: Innovative Grazing Practices and Riparian Restoration by Scott Richard Mitchell A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented March 5, 2020 Commencement June 2020 Master of Science thesis of Scott Richard Mitchell presented on March 5, 2020 APPROVED: Major Professor, representing Wildlife Science Head of the Department of Fisheries and Wildlife Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Scott Richard Mitchell, Author ACKNOWLEDGEMENTS I would like to thank all the incredible people and organizations that contributed to this project and its successful completion, both directly and through their support. First, I would like to thank my major professor, Dr. Sandy DeBano for all of her support, advice, encouragement, help in the field, and commitment to her students. Without Sandy this project would not have been possible, and I feel incredibly grateful to have had the opportunity to work with her for the past several years. My other committee members, Dr. Dana Sanchez and Dr. Gail Langellotto, both provided helpful suggestions and edits throughout the planning of this project and writing of this thesis, and always had useful advice. Critical to the completion of this work was funding from multiple sources, including a grant from the Foundation for Food and Agriculture (Research Grant #549031) that supported my NIFA Fellowship, the OSU Branch Experiment Station Internship program, the Oregon Department of Forestry and the United States Forest Service. Second, I would not have been able to complete this thesis and my degree without the support of the faculty members and staff at Oregon State University. Faculty and staff at the Hermiston Agricultural Research and Extension Center in Hermiston, and those at the main Corvallis campus contributed immensely to my ability to complete this project. I would especially like to thank Dr. Raymond Malewitz, at the Corvallis campus for his edits and tips on writing and the writing process as I began writing this thesis. The staff and researchers at The Nature Conservancy and the United States Forest Service Pacific Northwest Research Station were all critical to the completion of this project. In particular Mary M. Rowland and Heidi Schmalz helped immensely with the logistics of the project, some field work, and identification of some challenging plant species. Josh Averett was another person who contributed substantially to this project and taught me how to identify willow species in Starkey. Josh also contributed important feedback to the design and analysis of this work. I would also like to thank Skyler Burrows for all the work he did identifying all the bee specimens that were collected during this study and his responsiveness to all my questions. I would like to especially thank the field and laboratory assistants who helped us accomplish the monumental task of collecting and preparing tens of thousands of bees—washing, sorting, and pinning them. Special thanks to James McKnight, Marisa McCaskey, and Coltyn Kidd for all their hard work in both the field and the laboratory. I would also like to thank all of the other graduate students, both in the Department of Fisheries and Wildlife and those in the Pollinator Reading Group for providing friendship, support, and feedback on my work throughout the project. In particular, my fellow bee researcher and lab-mate Katie Arstingstall who helped with field work related to this project and helped supervise the interns who worked for us. Last, I would like to thank my family for always encouraging me and providing me with a rich upbringing that inspired me to pursue a career in science. My brothers and parents always encouraged my interest in nature and are probably the reason I decided I wanted to study bugs, flowers, plants, and ecology. I would also like to thank my girlfriend, Kenzie Fleischman, for her unwavering support in my pursuit of my degree. She has been a critical part of my life for most of my adult life and endured multiple years of long-distance, many late nights, and a move across state-lines to support my goals and aspirations. CONTRIBUTION OF AUTHORS Sandra J. DeBano contributed to all parts of this thesis including study design, implementation, data analysis, and writing in all chapters. Skyler Burrows identified all bee specimens collected in both studies. Mary M. Rowland contributed to the design and implementation of studies described in both chapters.