Impacts of preferential herbivory on tree species composition and seedling abundance in an Illinois closed-canopy forest site

Background/Question/Methods The suite of tree species present in closed-canopy forests is largely determined by tree species’ shade tolerance characteristics, site conditions, and response to herbivory.  The latter is particularly important in Illinois’ forests having high deer densities during winter months.  Repeated sampling of woody species in permanent plots at one such closed-canopy, mesic forest site (Funks Grove, Illinois) was conducted to assess the frequency of deer browsing and changes in species composition between 2003 and 2008.

Results/Conclusions The tree stratum is dominated by the shade-tolerant Acer sacharrum; however, Asimina. triloba and Fraxinus sp. (Ash) were the only taxa that showed an increase in seedling abundance.  Both species exhibited lower levels of herbivory than expected if deer had no browse preference.   The largest increase in seedlings between the two sampling periods occurred for A. triloba, which possesses powerful defensive chemical compounds that largely prevent damage from herbivores.  These results suggest that the composition of forest community tree species is chiefly being shaped by intense browsing at this site.  Furthermore, the effects of high A. triloba density on forest regeneration are not clearly understood and may substantially reduce species richness over time.