PARENT SESSION
Oral Session #86: Invasive species: Ants and other invertebrates.
Presiding: J. Morrison
Thursday, August 8. 1:00 PM to 3:45 PM. Greenlee Meeting Room, TCC.
Ecological consequences of exotic invaders: European earthworm impacts on native plant communities in hardwood forests.
Hale, Cindy*,1,2, Frelich, Lee2, Reich, Peter2, 1 The Natural Resources Research Institute, Duluth, Minnesota2 University of Minnesota - Twin Cities, St.Paul, Minnesota
ABSTRACT- European earthworm species have been invading previously worm-free hardwood forest ecosystems in Minnesota. These hardwood forests have developed since the last glaciation in the absence of native earthworms, and many stands historically had thick forest floors, that served as rooting medium for forest herbs and tree seedlings. The exotic earthworms consume the forest floor, sometimes leaving exposed mineral soil and the abundance and diversity of native plant species and tree seedlings decline steeply within a few years of earthworm invasion. This four year research program included (1) a detailed descriptive study to document the rates and patterns of change in the forest floor, upper soil horizons, understory vegetation and earthworm populations associated with leading edges of earthworm invasion; (2) a field-based experimental study to test for interaction affects between deer grazing and earthworm invasion on the recolonization or recovery of the understory vegetation following earthworm invasion; and (3) experimental greenhouse microcosms to examine the affects of different earthworm species and to investigate potential mechanisms of impact. The leading edge of invasion has advanced 20 meters in four years and is associated with a four-fold increase in earthworm biomass, the appearance of 7 earthworm species and decreases in plant diversity from 10/m2 to 2/m2, total cover from nearly 100% to less than 25% and tree seedling density from 100+/m2 to 1/m2. An earthworm-deer interaction is occurring, where both plant diversity and total cover are higher inside the deer exclosures compared to outside the exclosures when earthworms are present. The microcosm experiment indicates that different earthworm species have significantly different affects on the nature and magnitude of changes in forest floor, upper soil horizons and plant populations in response to earthworm invasion. The invasion of earthworms in hardwood forest ecosystems is an example where invasion leads to a cascade of ecosystem effects.
KEY WORDS: european earthworms, exotic species invasion, hardwood forests, understory plant communities