Shaping Pennsylvania's Forests: Effects of White-Tailed Deer, Soil Chemistry, and Competing Vegetation on Oak-Hickory Forest Understory Plant Community Compositio

Several factors influence plant community composition of forest understories, including browsing by white-tailed deer (Odocoileus virginianus), competitive interactions with other plant taxa, and soil chemistry changes due to acid deposition. Each of these factors has been extensively studied throughout the northeast, but to date no studies have attempted to understand their interactions and overall influence on forest understories in the Ridge and Valley Physiographic Province of Pennsylvania. This dissertation separates the relative importance of each of these factors using several approaches. In chapter 1, I use single-species occupancy models to better understand species-specific responses to soil chemistry and removal from deer browsing. In chapter 2, I use generalized joint attribute models to assess biotic interactions in the context of environmental predictors that explained occupancy of individual species in chapter 1. Chapter 3 culminates my research by presenting short-term (3-year) results from a full-factorial experimental manipulation of plant communities using liming (to improve soil chemistry), fencing (to exclude deer browsing), and herbicide application (to remove competing vegetation). My results highlight the importance of soil chemistry in shaping occupancy of plant taxa and indicate these relationships likely alter competitive interactions between species. Exclusion of white-tailed deer had no effect on occupancy, abundance, or flowering status of deer-preferred plants after 2 years, suggesting slow or limited recovery of these taxa immediately after protection from browsing. Additionally, short-term results from the experimental manipulation indicate that liming has positive effects on forest herb abundance and flowering status, and that competitive release has been achieved in response to herbicide application for non-competing vegetation. Overall, this study demonstrates that soil chemistry and competing vegetation interact to shape plant community composition, however, results should be considered preliminary. Continuous monitoring of these communities is necessary to better understand long-term trends in response to treatment and whether shifts in community composition persist through time.