Exotic Earthworm Communities within Upland Deciduous Forests of National Wildlife Refuges in the Upper Midwest

The invasion of exotic earthworms into forests of the Upper Midwest region of the United States is a considerable management issue due to the ability of earthworms to act as ecosystem engineers and modify existing ecosystems. Earthworm taxa differ in their biology and behavior, such that earthworm abundance and community composition can be related to the type and degree of alteration expected to occur. Many National Wildlife Refuges of the Upper Midwest have enabling legislation that identifies migratory birds as a specific management priority, and past studies have indicated that earthworm-modified forests provide lower quality habitat for migratory, ground-nesting birds. We quantified exotic earthworm community composition, abundance, and variability within and among upland deciduous forest stands at six of these refuges (Horicon, Ottawa, Rice Lake, Seney, Shiawassee, and Tamarac), providing a baseline for estimating the status of earthworm invasion. Analyses revealed a significant difference in mean earthworm biomass among upland deciduous forest stands sampled (ANOVA, F5,52 = 2.81, P = 0.03) and indicated significant differences in earthworm community composition (multiresponse permutation procedure, T = 212.57, A = 0.24, P \u3c 0.001) at each refuge. Based upon existing theories regarding earthworm invasion, we suggest that the stage, and impact, of earthworm invasion is varied across the region. Continued research and monitoring of earthworm communities should test this theory and seek to elucidate drivers of earthworm invasion patterns and impacts to forest ecosystems