PARENT SESSION
Oral Session # 73: Invasive Species VI: Terrestrial.
Presiding: S DeWalt
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 204.
Patterns of earthworm invasion and understory plant composition in lakeside northern hardwood forests.
Holdsworth, Andrew*,1, Frelich, Lee1, Reich, Peter1, 1 University of Minnesota, Saint Paul, MN
ABSTRACT- Current studies show that exotic earthworm invasion can significantly affect the understory plant communities and nutrient cycling of northern hardwood forests. However, little is known about the extent of earthworm invasion. We conducted a survey of understory plant communities, earthworms, soils, and tree composition in 314 plots located in 40 mature hardwood stands in the Chippewa and Chequamegon National Forests (Minnesota and Wisconsin, respectively). Stands were comparable in overstory composition, biomass, geology, and management history. In both regions we found a correlation between the presence of exotic earthworms and the presence of cabins, resorts, boat landings, roads, and campsites. The earthworm species most associated with duff loss (Lumbricus rubellus) was found in over two-thirds of the Chippewa and Chequamegon plots. The nightcrawler, L. terrestris, inhabited nearly half of the Chequamegon plots while only occupying 16% of Chippewa plots. However, earthworm-free plots were much more common in the Chequamegon, 19% vs. only 3% in the Chippewa. Plots with all three earthworm ecological groups (litter dwelling, upper soil dwelling, deep burrowing) had an average of 50% less sugar maple seedling cover and between 10 and 20% less plant species richness than plots with few or no earthworms. The abundance of the sedge Carex pensylvanica was significantly higher in plots with abundant earthworms. Our results further support other studies showing that exotic earthworms significantly alter the structure and composition of northern hardwood forest understory plant communities and that the invasion is in an advanced but incomplete stage.
Key words: invasion , plant composition, exotic earthworms, northern hardwood forest