As potent ecosystem engineers, non-native earthworms are altering the fundamental structure and function of previously earthworm-free hardwood forests in North America. European earthworms have been invading hardwood forests in the northern United States since European settlement. Discarded earthworms used for fishing bait is an important vector for their continued spread in the Lake Superior Coastal Zone as evidenced by the fact that invasions often radiate from boat landings, lakeshores, cabin, and roads. These forests developed over thousands of years in the absence of earthworms and historically had thick layers of leaf litter that serve as rooting medium for herbaceous and woody species. Following invasion of a northern forest by earthworms, a cascade of ecological effects occurs. The most obvious change initially is the loss of the previously thick forest floor. This loss is associated with large declines in native plants and tree regeneration, surface soils in these forests are compacted, soil erosion increases, and nutrient leaching occurs leading to decreased nutrient availability and potential degradation of adjacent wetlands and waterways through increased sediment and nutrient transport from impacted forest areas.
Research over the last decade has clearly demonstrated that human-mediated spread of earthworms is the primary vector of continued expansion of earthworms across the landscape, since natural spread of established populations is quite slow (>100years to go ½ mile). Therefore, identification and protection of earthworm-free areas in the Coastal Zone could substantially limit the impacts for generations to come.
Minnesota's Lake Superior Coastal Program; Project no. 306-13-03; Contract no. 00-0000011949
Exotic earthworm invasions: integrated research and education to achieve natural resource protection.
University of Minnesota Duluth.
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