White-tailed deer (Odocoileus virginianus) alter herbaceous species richness in the Hiawatha National Forest, Michigan, USA

To assess the effects of deer browsing on understory composition, we examined hardwood forests with documented differences in browse intensity within two regions of the Hiawatha National Forest in Michigan's Upper Peninsula. A deciduous twig damage assessment confirmed that two sites within the southern region experienced high white-tailed deer (Odocoileus virginianus) browse intensity (44-49% of twigs browsed) and two sites within the northern region incurred low browse intensity (0.5% and 0.6% of twigs browsed). We used within-site sample means and site-level rarefaction curves to compare understory species richness in these two forests. The forest experiencing low browse intensity had higher woody species richness on a per plot basis than the heavily browsed forest, but the converse was observed for herbaceous species richness. Site-level evaluation with rarefaction curves confirmed the plot-scale results for herbaceous species, but different patterns in woody species richness emerged due to differences in the distributions of species across the four sites. When graphed as a function of cumulative number of plots, we again found that a low browse site had the highest woody plant species richness, but a high browse site had the highest richness values when richness was graphed as a function of cumulative number of stems sampled. This study demonstrates that although species richness is a useful tool for describing ecosystems, results for the same sites can differ based on how species are grouped and on the scale of analysis.