INTERACTIVE EFFECTS OF LANDSCAPE CONTEXT, NON-NATIVE PLANTS, AND DEER ABUNDANCE ON FOREST PLANT COMMUNITIES IN CENTRAL INDIANA
Landscape context (land use and fragmentation), high densities of white-tailed deer, and non-native plants have all contributed to reductions in native plant diversity in forests across the eastern United States. These processes and their impacts on plant communities have produced ecological, economic, social, and human-health concerns, emphasizing the need to better understand these processes and their impacts to effectively guide management across the rural-urban gradient. However, management is further complicated due to the related and interactive nature of these processes. While some research has examined interactions among landscape context and invasive species, as well as invasive species and white-tailed deer, we found few studies that simultaneously considered all three of these threats to native forest plant communities.
We studied forest patches in central Indiana in both agricultural (rural) and urban matrices to determine how deer herbivory varied with landscape context. Specifically, we examined how deer abundance, browse on woody species, non-native plant species cover and densities, land cover, and forest patch area/shape impacted herbaceous-layer and sapling-layer species diversity. Our results demonstrated that woody browse available to deer differed between rural and urban forest patches. Additionally, we found that deer browsed the invasive shrub, Amur honeysuckle (Lonicera maackii) at a higher rate in urban forest patches compared to agricultural patches. We also observed that deer, non-native plant densities and cover, and landscape context were all associated with changes in native plant species diversity. Higher rates of deer browse, non-native plant density/cover, and increased forest edge were associated with declines in diversity. Interestingly, we found that the proportion of forest land cover in close proximity to forest patches was not only correlated with increased native plant species, but also associated with reduced negative effects on diversity from non-native species. We did not observe any interactions between deer and non-native plants or deer and landscape context variables. Both rural and urban landscapes in our study were highly fragmented and adding a heavily forested landscape would contribute to an improved understanding of how landscape context, deer herbivory, and non-native plant species affect native plant communities. Managers should be aware that forest patches with increased edge and a lack of other forest land cover located within 500 m are susceptible to declines in diversity associated with non-native plants. While observed rates of deer browsing in our urban forest patches were low compared to examples in the literature, managers should also be aware that deer often exceed desired densities in urban settings, which could further harm at-risk plant communities.