European earthworm species have recently begun to invade hardwood forest ecosystems in the northern United States. Many of these forests have thick forest floor layers that serve as the rooting medium for forest herbs and tree seedlings. Exotic earthworms consume the "duff" layer, sometimes leaving exposed mineral soil. Although there is significant concern about the potential loss of native forest plant species and ecosystem stability, little is known about how plant communities and ecosystems respond to invasion by detritivores (detritus-feeders). The overarching hypothesis of the study is that earthworm invasion will have cascading effects on soil characteristics and forest-floor vegetation, and that resilience of the community will depend on site productivity and interaction with deer grazing. This study will employ deer exclosures, field studies, and experimental manipulations to determine rates and patterns of change in earthworm populations, assess effects of earthworm species on forest floor and understory vegetation, identify factors affecting vegetation recovery following establishment of earthworm populations, and examine earthworm impacts across a site productivity gradient. This study will lead to increased understanding of the process of invasion by exotic animal species and will have significant implications for forest management and restoration.
