Associational effects, landscape context, and plant height affect white-tailed deer (Odocoileus virginianus) browse selectivity in oak woodlands

Abstract

Questions Large spatial variation in damage intensity is a pervasive, but poorly explained, feature of herbivore?plant interactions. To predict herbivore effects on plant communities, ecologists need greater understanding of the mechanisms and relative importance of processes driving variation in damage at the spatial scales of individual plant, plant community, and landscape. We ask: (1) what are the relative strengths of traits of individual plants versus landscape context in affecting white-tailed deer (Odocoileus virginianus) browsing on saplings in oak woodlands; and (2) is browsing intensity on post oak (Quercus stellata) influenced by associational effects related to density or frequency of more-selected or less-selected species? Location Dry oak-dominated woodlands, Kansas, USA. Methods We sampled deer browsing on saplings in three woodlands, each containing five transects, with 21 10-m2 plots per transect. Transects ran from woodland?grassland edges into woodlands. In each plot, we identified saplings to species, measured variables in individual-plant (height) and landscape contexts (distance from edge and proximity to deer trails), and quantified proportion of stems browsed per sapling. Results Browsing intensity varied greatly among the 18 tree species encountered. Browsing increased with sapling height and decreased with distance from woodland edges. The effect size of distance from edge was twice that of sapling height, although both effect sizes were small. Browsing on post oaks increased with local frequency of saplings of more-selected species. Conclusions Our comparison of individual-plant versus landscape context variables and our assessment of associational effects supports a substantial role for coarse-scale foraging decisions in explaining browsing damage. However, sapling species identity was most influential. Associational susceptibility of a less-selected species, post oak, near more-selected neighbors is consistent with a mobile herbivore choosing between patches. The pre-eminence of frequency of more-selected species in mediating associational susceptibility may reflect decreased handling time in pure patches and/or attempts to balance nutrients.