Intro and Brief History

Northern forests are experiencing multiple stresses and changes, including nutrient deposition and acidification, disease and pest outbreaks, changing climate, and biological invasions. Biological invasions in northern forests threaten to alter ecosystem structure and function, especially when they change the habitat of other species, alter the availability of key resources, or compete with or replace native species. Much of the focus on exotic species invasions in forests and other ecosystems has been on above ground invaders, which are the most obvious. However, belowground invasions may be equally widespread and may become better known as more ecologists begin to recognize the importance and links between aboveground and belowground communities. One invasive species that is receiving more and more attention is the exotic earthworm. (Bohlen et al 2004)

Many people in the United States grow up considering earthworms a native part of the natural world. What these people do not know is that earthworms were not always part of the Minnesota landscape. (UMN 2005) For over 12,000 years Minnesota's forests developed without the influence of earthworms. Any North American earthworm species that did inhabit Minnesota were extirpated during the last glaciation. (James 1990) In the absence of earthworms, "fallen leaves accumulated and developed a thick duff layer on the forest floor that provided an excellent rooting zone for herbs and tree seedlings." (Reynolds et al. 2002)

Currently, over 15 species of European earthworms inhabit Minnesota. (Reynolds et al. 2002) Over the last 150 years European Earthworms were likely accidentally and intentionally introduced with the importation of plant material and soils from Europe and the use of worms as fishing bait across the region. Ongoing studies suggest that invasive European earthworms have a notable effect on the forest floor, forest understory, canopy, plant diversity and composition (Hale), nutrient cycling (Groffman et al. 2001) and soil properties.

Since the 1980's forest managers on the Chippewa National Forest have been concerned about the loss of understory plant cover and diversity in areas with high earthworm populations. For example, "Exotic earthworms are considered a major factor in the population decline of the state threatened goblin fern, Botrychium mormo." (UMN 2005)

Earthworm species are divided into three broad ecological groups: epigeic, endogeic and anecic.

Since the glacial ice sheets retreated from the northeast region of the United States and Canada about 10,000 years ago, large stretches of hardwood forests have developed over much of the landscape with a variety of tree species. The hardwood forests also provide habitat for hundreds of other organisms such as dozens of plant species, small and large mammals, insects, amphibians, mollusks and hundreds of soil organisms like fungi and bacteria. (UMN 2005)