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Invasion of European Earthworms E-mail
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Wednesday, 20 June 2007

Invasion of European Earthworms

INVASION OF EUROPEAN EARTHWORMS INTO A NORTH AMERICAN ASPEN FOREST:
EFFECTS ON SOIL CHEMISTRY, MICROFLORA, FAUNA, AND VEGETATION

Eisenhauer, N. & Scheu, S.

Darmstadt University of Technology, Institute of Zoology, Schnittspahnstrasse 3, D-64287 Darmstadt

After the last glaciation earthworms, which had taken refuge in the southern parts of the continent, did not recolonize North America. They have invaded the region which today is Canada since 1500 AD when European settlers colonized the continent and were distributed by inadvertent or intentional human activities.

Earthworms are known to alter soil structure, nutrient cycling and the complex interactions between soil fauna and microflora and therefore likely affect aboveground plant communities. However, the impact of these ecosystem engineers on soil microbial and soil mesofauna communities has only been studied recently.

In this study the effect of invasion of earthworm species (Dendrobaena octaedra, Lumbricus terrestris and Octolasion tyrtaeum) into a western Canadian aspen forest on soil fauna, microbial and plant community and soil chemistry were investigated.

Along three transects (200 m) starting at the edge of the forest, densities of earthworm species were determined. Plants were harvested, and separated into three plant functional groups (herbs, grasses, legumes) and the dry weight was measured. In addition, soil cores were taken to investigate the effects of burrows of L. terrestris on soil fauna, microflora and soil chemistry.

The invasion of L. terrestris und O. tyrtaeum in the investigated aspen forest is still progressing. O. tyrtaeum was very abundant in the middle of the forest. As shown previously, invading species initially may reach high abundances due to high resource availability. In contrast to D. octaedra, L. terrestris and O. tyrtaeum did not invade from a forest road close to the aspen forest. Probably, they invaded laterally from a little creek nearby the aspen site.

Chemical and microbial parameters were altered only in the litter layer in L. terrestris burrows. L. terrestris incorporated litter into the soil and O. tyrtaeum mixed it with the mineral layers. Consequently, the organic layers disappeared where both species occurred together. Microbial biomass was reduced where L. terrestris and O. tyrtaeum were present. This was probably due to resource competition and mechanical disturbances. Structural and chemical properties of the soil and the plant community were altered when L. terrestris and O. tyrtaeum were present. Some plant species benefited from earthworm presence, others did not. The presence of O. tyrtaeum reduced microarthropod densities (-75 %) and diversity (-29 %) through mechanical disturbances, increasing compactness of the soil and resource competition.

The invasion in the investigated aspen forest by mineral soil dwelling earthworm species presumably is slow due to the climatic restrictions on growth, reproduction and activity of these species. However, this study indicates that earthworm invasions can have dramatic impacts on vegetation, soil microarthropods, microorganisms and soil chemistry.

 

 
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