[compost_tea] Re: non-native species of earthworms

From: chris reid <reidchris_at_earthlink.net>
Date: Thu, 12 Jun 2003 08:38:42 -0400

Kirk Leonard wrote:

Autumn -- With respect to changing forest ecosystems in New York state, I
think acid rain and human impacts are a great deal greater than worms could
ever cause... I would also point out that "worm invasions" are more likely
a result of discarded fishing worms than of worms actually invading
anywhere. They will go where we put them and where they can live, and I for
one believe they will do no harm. Worms live on decaying organic matter,
never on live plants. Human impacts on the land are both larger and more
questionable. -- Kirk


As a gardener who has an interest in ecological issues, I have actually done
a bit of reading and also exchanged correspondence with a researcher on the
topic of exotic earthworm species and their impact on ecosystems. Autumn's
description of the impact of earthworms on ecosystems matches what I have
read in the research that has been published. There are not a lot of people
studying worms but some people are trying to understand what the impacts are
with large numbers of atypical earthworms. One thing that can occur is that
the rate at which the forest duff is reduced changes dramatically. This
takes its toll on niche player type plants that require a certain amount of
moisture in the soil, and may find the microclimate changed when the duff is
digested and there is no natural mulch to hold the moisture into the soil.
In a study in New Jersey, as I recall, there might have been an impact from
a change in nitrogen levels in areas where a particular worm was found
(probably the so-called Asian earthworms) and barberry, an invasive plant in
the Northeast, seemed to be taking hold more readily.

The notion of earthworms being introduced into forests by people fishing
corresponds to the experience in northern Minnesota with the decline of the
goblin fern, which appears to be related to Lumbricus rubellus (Ok folks,
not a scientist and including Latin name from memory), red angle worms,
which were discarded in the forest by fishermen.

I don't think that was the source of all of them, but the important thing is
to note that research is being done on this topic. Here is an example of a
paper considering the issue of the impact of earthworms on ecosystems. It
is very helpful on this topic to hew to what is known and be specific,
because it helps in keeping a clear understanding of the phenomena that are
being observed.

http://www.ecostudies.org/research/reports/grofrep2.html#05

I got interested in this topic when I started a garden in an area infested
by weeds, and I noticed that the soil was very, very loose and fluffy -- I
didn't measure, but my feet sank in it and I bet it was 4 - 5 inches of just
fluff, which, er, is the technical term :). I found several balls of large
worms which I later learned were the Asian type (they wriggle differently
than the night crawlers I know of from childhood, and this tendency to form
large balls of worms is also apparently a characteristic of them).

To read more via the internet on this topic, search Patrick Bohlen or Peter
Groffman's names. The barberry research was out of Rutgers, the goblin fern
research I think was paid for by National Geographic or reported there
anyhow. Institute for Ecosystem Studies in Millbrook, NY has several
scientists collaborating on this topic. Patrick Bohlen is at the Archibald
Research Station in Florida, and Cornell has some people working on this
area as well.

The researchers are comparatively conservative in their claims about what is
happening in the ecosystems (that is, compared to some of the media coverage
that hypes it up a la "the sky is falling"). However, there are numerous
ways in which soil is impacted and if certain worms are contributing to
creating a complex of factors that bodes ill for native plants, there is
value on realizing the potential problem sooner rather than later, and
having to take only a little corrective action instead of being faced with a
major disaster. To see what happens when "it's not really a problem" is the
guiding approach in ecological interventions, I find the book Killer Algae
instructive.

How does this relate to making compost tea? Maybe: know what species you
are using to create vermicompost, and be clear on the impact, if any, on the
environment of their escape. Don't throw your fishing worms into the woods,
especially in the Boundary Waters in Minnesota...

Chris Reid


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Received on Thu Jun 12 2003 - 09:01:46 EDT

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