Influence of deer browsing on invasive and native vegetation in a maritime forest

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Dessa Dunn, Odum School of Ecology, University of Georgia, Athens, GA and Elizabeth King, Center for Integrative Conservation Research, University of Georgia, Athens, GA

Background/Question/Methods
The camphor tree (Cinnamomum camphorus) was introduced from Asia to the subtropical portions of the southeastern United States over 100 years ago and is naturalized in many areas. In recent decades, however, it has become increasingly abundant in maritime forests on Jekyll Island, an Atlantic Ocean barrier island in Georgia. Native white-tailed deer (Odocoileus virginianus) populations have also increased during this period. We sought to explore whether deer herbivory may be limiting native understory vegetation cover and abundance of native hardwood tree seedlings and whether the less palatable camphor seedlings in turn show increased abundance and growth. We established 22 6x6m plots in a 40ha area with heavy camphor proliferation, of which 11 were fenced to exclude deer and 11 were not. Each plot was subdivided into 25 1x1 m quadrats. In April 2018, in each quadrat we counted, tagged, and measured height and leaf number of each camphor seedling. We also recorded total herbaceous vegetation cover, cover by species, and abundance of hardwood tree seedlings. Plots were re-measured in July 2018, September 2018, May 2019, and May 2020 also tagging and measuring newly emerged camphor seedlings at each census.
Results/Conclusions
Deer herbivory was associated with decreased native understory vegetation cover but did not have an immediate effect on the abundance of native tree seedlings or species richness. Vine species like Vitis rotundifolia especially benefitted from excluding deer, yet camphor seedling growth and survival also increased when deer were excluded. Although longer-term herbivory effects on camphor versus native species in this environment are not yet known, these results suggest that controlling deer herbivory may not tip the balance of apparent competition balance back toward native vegetation, and other restoration efforts are likely needed to control camphor invasion and support the native tree and plant community.