COS 8-10
Concurrent effects of forest management and white-tailed deer herbivory drive spatial patterning in herbaceous-layer plant communities
Concurrent disturbances can interact to affect the diversity and spatial structure of forest understory plant communities. Forest management and deer herbivory are two common disturbances that often occur concurrently. Plant communities in canopy gaps tend to be dominated by ruderals due to increased resource availability, whereas communities browsed by deer generally lack palatable species intolerant to herbivory. Such responses are usually measured at the gap scale, although spatial heterogeneity in resources and herbivory pressure can vary at finer spatial scales. We used the Bray-Curtis dissimilarity index (BC) and spatial modeling techniques to examine patterns in fine-scale (0.5-m – 6.0-m) community similarity within, on the edge of, and in closed-canopy forest near canopy gaps (1.25-ha – 4.43-ha), within and outside of deer exclosures. We expected stronger spatial patterns in gap centers compared to the adjacent forest, and expected deer herbivory to either increase or decrease the complexity of community structure. An increase may occur if herbivory is patchy and does not affect the entire gap evenly, whereas heterogeneity may decrease if herbivory reduces abundance of, or extirpates, sensitive species. Study sites included eight management openings in south-central Indiana. Vegetation sampling occurred during the third growing season after canopy removal using 12-m intersecting transects.
Results/Conclusions
Less than three years after harvest, management and deer herbivory affected the spatial structure of herbaceous-layer plant communities, but differences in whole-community species richness and evenness differed only by management. Herbaceous-layer plant communities displayed greater heterogeneity within canopy gap deer exclosures compared to unfenced communities. Spatial models of BC tended to be less complex (two parameters in best model) in unfenced compared to fenced plots. The separation distance at which BC stopped increasing was 2.60-m in the center of clearcut exclosures, whereas BC in open plots increased linearly over the 6.00-m sampling extent. Plots located between the center and edge did not differ in spatial structure, but overall species composition was more similar in unfenced (BC = 66.0) compared to fenced (BC=76.2) plots. In the surrounding undisturbed forest, fenced plant communities were more homogeneous (patch size = 2.74-m fenced; 0.86-m unfenced). In managed landscapes, deer herbivory is likely concentrated within forest openings where forage availability is greater, resulting in more spatially-homogeneous plant communities. Deer foraging pressure is more dispersed in the surrounding forest, which can lead to greater heterogeneity.