PARENT SESSION
Poster Session # 9: Herbivory.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Regional and local effects of white-tailed deer herbivory on vegetation structure and composition in northern hardwood forests.

LeBouton, Joseph^*,1, Laurent, Edward¹, Walters, Michael¹, Liu, Jianguo¹, ¹ Michigan State University, East Lansing, MI

ABSTRACT- Many studies of northern hardwood forests in the U.S. link high levels of white-tailed deer herbivory with low seedling and sapling densities and altered herbaceous community composition. We hypothesized that the juxtaposition of vegetation patches on the landscape is a critical factor affecting local white-tailed deer densities and their subsequent effect on the vertical structure and species composition of forest plant communities. We tested this hypothesis across a regional winter deer density gradient (0-20 deer/km²) using a network of 143 vegetation plots in a 500,000ha study region in the Upper Peninsula of Michigan. Within each plot we sampled herbaceous vegetation, three size categories of tree seedlings and saplings (<0.25m tall, 0.25-1.5m tall, and >1.5m tall-10cm dbh), and canopy composition. We compared forest vertical structure and community composition data to regional white-tailed deer winter population indices from 1956 to present, controlling for forest management history. We also compared present vegetation to landscape composition indices around each plot, including edge density, landscape connectivity, and distance to key white-tailed deer habitat types. Seedling and sapling density and species composition varied in response to regional white-tailed deer winter population density, forest management history, and the landscape composition around each stand. Plots within high winter deer density regions and local landscapes favorable to high winter deer densities (e.g., stands near winter deer yards) exhibit less vertical structure and fewer seedlings, saplings, and canopy recruits than plots within low winter deer density regions and/or in local landscapes that are far from key deer habitat. In contrast, understory community composition showed little response in species richness but a large response in community evenness to regional deer density and local landscape composition. Species avoided by white-tailed deer (e.g., mat-forming Carex species) had much higher dominance within high winter deer density regions, regardless of local landscape composition.

Key words: White-tailed deer herbivory, Vertical forest structure, Landscape composition, Plant community composition