earthworms Lumbricus rubellus & rare native fern Botrychiummormo

**G*@aol.com**

The following Dispatch appeared in Frontiers in Ecology and the Environment 
vol. 1

no. 1 February 2003, published by the Ecological Society of America.

I'm posting it to the GWL because some members were interested in writing

about the topic. I copied it (with editor Sue Silver's permission) because it 
didn't come up in web searches, it answers questions I had and possibly yours 
too, it mentions research sources, it mentions ways earthworms can be spread 
that other articles didn't, and only subscribers have full access to the 
journal (you can preview the latest issue but not this one) on the Society's 
website www.esa.org

I highly recommend the site. 

Sally
Editor, Garden Literature index

Earthworms as bad guys 

Kathryn Senior

    Areas of North America that were covered by glaciers do not have native 
earthworm populations, but there is new evidence that invading species, 
primarily from Europe, have now infiltrated this area. Rather than benefiting the 
soil, the worms appear to be causing problems for rare plants. Author Michael 
Gundale (Michigan Technological University, Houghton, MI, currently at University 
of Montana, MT) has found that 'exotic' earthworms effect subtle alterations 
in the forest floor that can disrupt the growth of rare ferns such as 
Botrychium mormo. "Of the two abundant earthworm species, Dendrobaena octaedra  and 
Lumbricus rubellus, the latter was significantly associated with the 
disappearance of B. mormo", he says.

    Gundale studied populations of B. mormo that had been previously mapped 
by researchers at the Chippewa National Forest in 1996. He surveyed 28 of the 
mapped and counted populations and compared the fate of B. mormo in areas that 
had different levels of exotic earthworm invasion. The earthworm type and 
population level were obtained by sampling worms by hand and by liquid extraction 
in a 25 cm by 25 cm plot. Soil cores from each area were also analysed. The 
presence of D. octaedra had very little effect on the forest floor, but L. 
rubellus, which is known to disturb and distribute organic matter in the soil, was 
associated with the decline of B. mormo populations. Gundale carried out a 
controlled laboratory microcosm experiment and showed that, in areas where it was 
present, L. rubellus was able to create the soil conditions found on the 
forest floor (Conserv Biol

2002; 16: 1-8).

    "B. mormo depends on mycorrhizae to obtain carbon and nutrients from the 
soil, and it is plausible that the success of the fern is directly related to 
the health of its subterranean mycorrhizal network, something that could be 
easily damaged by the activity of L. rubellus ", says Gundale. But how did 
European earthworms get to this remote area of the northern USA? One clue comes 
from Gundale's observations on the density of earthworm populations. "When an 
invasion was present, it became less severe as I moved further from an access 
road running through the area", he

reports. It seems likely that eggs of L. rubellus could survive on tires and 
be deposited on these isolated roads, effectively seeding the environment. He 
suggests that future work should concentrate on understanding how exotic 
earthworms influence the ecosystem; on the basis of the current study, efforts 
should be made sooner rather than later to restore invaded forests and prevent 
further invasion.

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