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US Fish & Wildlife Service FieldNotes

Exotic Earthworms May Be Affecting Shiawassee National Wildlife Refuge Forests

Region 3, December 19, 2012
A day’s worth of earthworms.
A day’s worth of earthworms. - Photo Credit: n/a
Pouring mustard solution into an earthworm sampling box.
Pouring mustard solution into an earthworm sampling box. - Photo Credit: n/a

An article was published in the most recent Journal of Fish and Wildlife Management that indicates that earthworms introduced from Europe may be adversely affecting the forested ecosystems of Shiawassee National Wildlife Refuge. A joint study between Michigan Technological University and the U.S. Fish and Wildlife Service’s Laurentian Mixed Forest/Great Lakes Coastal Biology Network showed that Shiawassee Refuge had the second largest mean biomass of nonindigenous earthworms of six Upper Midwestern refuges surveyed.

The other sites were Ottawa, Horicon, Rice Lake, Tamarac, and Seney National Wildlife Refuges. Seney Refuge had the lowest introduced earthworm biomass while Horicon Refuge had the highest. The exotic earthworm invasion into deciduous forests in the Upper Midwest has been a growing concern for forest managers in recent years. Earthworms are considered to be ecosystem engineers because their feeding activities hasten decomposition and removal of leaf litter and other organic materials on the forest floor.

Earthworms have been shown to cause changes in soil structure, nutrient availability and microorganism communities. Exotic earthworm presence has been linked to decreased plant diversity and increased dominance of invasive non-native plants. Also, recent research has shown decreased songbird and salamander abundance in woodlands with an abundance of introduced earthworms. In addition, earthworms are expected to negatively act in combination with other drivers of accelerated ecosystem change such as over abundant white-tailed deer populations, invasive plant species and climate change.The abundance of earthworms at Shiawassee Refuge may be a result of human influences. In general, those refuges which were surrounded by anthropogenic covers, such as developed land and agriculture had greater earthworm biomass than refuges surrounded by less anthropogenic cover. The introduction and spread of earthworms, over both short and long distances, has been greatly facilitated by human activity. Earthworms are commonly introduced into new sites by release of fishing bait and transport in soil and horticultural material, and on vehicles. The most common earthworms found at Shiawassee Refuge were the common earthworm or nightcrawler (Lumbricus terrestris) and the European earthworm or red wriggler (L. rubellus). No native earthworms were found at the refuge.To see the full article, visit the Journal online.

Contact Info: Steve Kahl, 989-777-5930, steve_kahl@fws.gov