Interactions between disturbance and ungulate herbivory in a northern hardwood forest

Background/Question/Methods

Canopy gaps generally enhance plant community heterogeneity in forested ecosystems as a result of the differential response of forest species to variation in opening size.   However, interactions between opening size and foraging patch selection by white-tailed deer (Odocoileus virginianus) may lead to changes in post-disturbance plant community development with important implications for biodiversity conservation and forest management.   We examined the influence of herbivory and canopy gap area on post-disturbance plant community dynamics in a managed hemlock-northern hardwood forest in the Upper Peninsula of Michigan. Twenty canopy gaps were created during the winter of 2002-03: seven small gaps (50 – 150 m²), seven medium gaps (151 – 250 m²), and six large gaps (251 – 450 m²). Within each gap, we established 4 -12 sample plots (depending on gap size). In 2005, 1 - 3 randomly selected subplots per gap were enclosed with wire mesh to exclude deer.  Gaps were revisited and intensively sampled in 2007.

Results/Conclusions

After 5 growing seasons, ground-layer plant communities in control plots were more similar compositionally than exclosure plots.  Control plots in small and medium gaps were more similar to control plots in large gaps than they were to exclosure plots in their respective gap size class.    Shade-tolerant forbs and trees were less common outside exclosures, while generalist species associated with higher understory light levels and exotics, were more prevalent outside exclosures. Our results suggest that white-tailed deer herbivory may influence the developmental trajectory of post-disturbance plant communities and be a mechanism for decreasing β-diversity along environmental gradients.