The influence of white-tailed deerand landscape composition and structure on exotic plant success

Plant communities are shaped by a variety of interacting factors including geographic constraints, abiotic, and biotic factors. The research contained herein investigated how these factors interact to influence exotic plant invasions. In the Northeastern United States, the highly abundant native white tailed deer (Odocoileus virginianus Zimm.), and landscape fragmentation are known to facilitate plant invasion independently. At the same time, biologically diverse native plant communities are broadly expected to limit invasion. In this work, primary producer-consumer interactions, plot-level native diversity, and surrounding landscape configuration were investigated to assess their association with exotic plant invasion across the region.;Using floristic composition data from 24 deer exclusion research sites distributed across the Northeastern US, the effect of deer on exotic versus native plants was investigated at species and community levels. Results indicated that deer facilitate the abundance of some exotic plant species, but inhibit the presence and abundance of many natives. While deer did not alter absolute exotic plant richness or abundance, they increased the degree of plant invasion due to strong declines in native plant abundance. Deer altered species composition and lowered native plant richness and abundance, causing an overall reduction in Shannon diversity (H').;To understand why some exotic species increased and others decreased in response to deer across the region controlled multiple-choice deer preference trials were conducted. Using captive deer, relative preferences for eight invasive exotic plants and seven native plants that are currently widespread and occur frequently in the region were determined in spring, summer, and autumn. Even though deer consumed more native plant biomass overall, preferences varied strongly at the level of species. This suggests that deer facilitate the invasion of exotic plants that are relatively unpalatable due to preferential selection of palatable plants.;Last, the relative importance of site-level white-tailed deer density, multiple landscape fragmentation metrics, and plot-level native plant diversity were tested for their roles in explaining plant invasion patterns in forest understory communities. The same pooled, floristic community data from 24 sites in the Northeastern US was analyzed using a series of nonparametric and parametric, multivariate and univariate statistics to illustrate the effects of multiple factors and their interactions on several measures of plant invasion. Deer, landscape structure and composition, and native species richness all affected patterns of exotic plant invasion. Results showed that deer density was highly correlated to landscape structure and that, as deer density increased, the percentage of exotic plant species also increased. Generally, landscape fragmentation was positively correlated with plant invasion. However, several interactions among deer presence, native plant diversity, and landscape attributes were identified. Exotic plant richness increased with native plant richness, but some evidence was found for native plant diversity limiting the degree of invasion in non-fragmented landscapes. Overall, to more fully understand the factors that influence plant invasion, the context of deer abundance, surrounding landscape structure and composition, and native plant species diversity must be considered.