Wednesday, August 8, 2012
Exhibit Hall, Oregon Convention Center
Background/Question/Methods: Both deer browsing and invasive plants have strong effects on eastern deciduous forest communities. Selective browsing on herbaceous plants and saplings by white-tailed deer (Odocoileus virginianus) reduces palatable species and increases unpalatable plant species. At the same time, exotic plants, such as Amur honeysuckle (Lonicera maackii), often dominate gaps and edges in forest, have rapidly decomposing litter, and decrease densities of native forest floor plants. Changes in understory plant communities from deer browse and shrub invasion may have cascading effects on soil invertebrates, which have key roles in forest ecosystem processes. Ants (Hymenoptera: Formicidae) are highly sensitive to biotic and abiotic changes and are widely used as indicators of ecosystem disturbance or recovery. The goal of our research is to determine the direct and indirect effects of invasive honeysuckle and deer, and their interaction, on plants and soil-dwelling ant communities. We test two main hypotheses: (1) white-tailed deer reduce diversity and modify species composition of ants by decreasing forest floor plant diversity; and (2) Amur honeysuckle reduces ant and modifies species composition by increasing the decomposition rate of litter. We established 5 pairs of deer exclosure and control plots in areas of similar topographic position, forest stand composition, and honeysuckle invasion. Exclosures are 20 x 20-m fenced (3-m high) areas, and paired control plots are located within 50 m of exclosures. In both the experimental and control plots, honeysuckle was removed from half (10x 20-m) of each plot, creating a split-plot design. Baseline data on ant and forest floor plant communities were collected in spring and summer 2011, the first growing season after plots were established, and analyzed with generalized linear mixed models.
Results/Conclusions: There were no significant effects of deer exclusion, honeysuckle removal, or their interaction on baseline ant or plant species richness, or leaf litter mass. Mantel tests showed a significant relationship between the turnover in plant and ant species composition among plots and sites when honeysuckle was removed (Mantel r = 0.6088, p = 0.0407), but no significant relationship between plant and ant species composition when honeysuckle was retained (Mantel r = -0.5121, p = 0.9205). Parameters will be measured annually on these plots to detect effects that manifest over time.