Document: CIN-3-48-6

Impacts of invading European earthworms on understory plant communities in previously worm-free hardwood forests of Minnesota.

HALE, C.M.*, L.E.FRELICH and P.B.REICH

University of Minnesota, St. Paul, MN 55108 USA ¹

Abstract:
During the last few decades, European earthworm species have been invading hardwood forest ecosystems in the northern tier of states in the U.S. These hardwood forests have developed since the last glaciation in the absence of native earthworms, and many stands historically had thick forest floor layers, that served as rooting medium for many species of forest herbs and tree seedlings. Leading edges of earthworm invasion have been identified in the Chippewa National Forest of northern Minnesota and a pilot study was conducted. Our objectives were to elucidate the rates and patterns of change in earthworm populations, forest floor and upper soil horizons, herbaceous understory vegetation and seedling demography related to the visible leading edge of earthworm invasion in previously worm-free hardwood forests. A 30 by 150m grid of nested sample plots (45 sample points) was established perpendicular to the visible leading edge in 4 northern hardwood sites. Forest floor thickness, herbaceous plant diversity and tree seedling density decreased dramatically with increasing earthworm biomass. Successive appearance of 5 different earthworm species and replacement of the E horizon by an A horizon were also associated with the visible leading edge. Heavily impacted stands have been observed with only one species of native herb and virtually no tree seedlings remaining. Therefore, concerns have been raised about the widespread loss of native forest plant species and the stability of hardwood-forest ecosystems.

Keywords: species invasion, temperate hardwood forests, earthworms, understory vegetation

This abstract is being presented at: 11:00 AM in session:
Oral Session #26: Invertebrate Herbivore - Plant Interactions.