http://www.gristmagazine.com/dearme/holdsworth090203.asp?source=newtoday
Alien
Worms Uproot Hardwood Forests in Minnesota (Grist Magazine)
Andy Holdsworth, conservation biologist
Andy Holdsworth is
a PhD candidate in conservation biology at the
University of Minnesota. He studies the ecological effects and
conservation implications of nonnative earthworms in Minnesota
and Wisconsin.
Monday, 02 Sep 2003
MINNEAPOLIS, Minn.
- There is a blurry line between work and
play in my life. My wife, Hillary, learned this lesson for the
Nth time this Labor Day weekend. She agreed to help me with
one day of field research in exchange for a day of unscheduled
canoeing and a day visiting a friend at a cabin in northern
Wisconsin. As agreed, after six hours (less than a day!)
of counting bunches of sedges (grass-like plants) in
my research plots, we gleefully headed off to play in the
Porcupine Lake Wilderness Area of the Chequamegon National
Forest in northern Wisconsin. We portaged Moxie (our canoe)
a half mile and slipped onto the lake for a leisurely
afternoon paddle. With Hillary napping in the bow and
me gazing at the wheeling and courting dragonflies, leisure
seemed to have set in very nicely. Then I suggested we paddle
to the shore and go for a little hike along a tributary stream
...
We sauntered along
admiring the pretty forest. Within five
minutes, however, I couldn't resist the urge to start scraping
at the dead leaves on the ground. I had seen a distinctive
lumpiness in the layer of leaves. I grabbed one of these lumps
and below it I found what I expected: the burrow of Lumbricus
terrestris, the earthworm that we all know as the "nightcrawler."
A foot away I found another and another and they continued for
half a mile along the stream. Chatting with Hillary about her
dreams of traveling to Cuba, I thought my earthworm curiosity
was satisfied until I walked about 200 yards away from the
stream and found "the leading edge." "Hillary,
we can
go to Cuba if we find the rest of this leading edge."
On the stream side
of the edge, the layer of leaves
was very thin and the ground was very hard underfoot,
like pavement. Once we crossed over the leading edge the
ground was like walking on a cushion with a thick covering
of dead leaves. What made the difference? Earthworms.
Apparently, fishermen dumped their leftover bait worms
beside the stream and they spread about 200 yards into
the forest. Across the leading edge there were no earthworms.
I dispatched Hillary to confirm there were no earthworms
further in the forest while I whipped out my GPS unit
to map this leading edge. Wow, cool isn't it? Okay, what
other response would you expect from a guy whose friends
call him "worm boy" or "earthworm Andy"? What
is the big deal?
The leading edge we
found was made by several species of
nonnative earthworms. In fact, all of these earthworms are
from Europe. Until European settlement of Minnesota and
Wisconsin (and most of the northern edge of the United
States), there were no earthworms working the soil. Yup,
the last glaciation that ended about 11,000 years ago wiped
out any earthworms that were in this region. For thousands
of years, the forests and grasslands of this region developed
without the influence of earthworms. When European settlers
brought their fruit trees and other plants to the New Country,
they inadvertently brought their Old Country earthworms.
The use of earthworms as fishing bait has further scattered
nonnative earthworms across the landscape. Until about
30 years ago, nobody thought anything of this.
Another graduate student
in my lab
(http://www.cnr.umn.edu/forestecology/home.html)
has started studying these leading edges of earthworm invasion.
She has found that the invasion of nonnative earthworms reduces
the number of understory plant species by half and significantly
reduces the cover of these plants, leaving mostly sedges and
Jack-in-the-pulpit (check out photos and more info)
(http://www.nrri.umn.edu/worms/withoutunderstory.html).
This change results
in the complete loss of the duff layer,
or the partially decomposed leaf fragments (see photos of
this, too) (http://www.nrri.umn.edu/worms/withoutsoils.html)
Without earthworms to incorporate this thick leaf mulch into
the topsoil, forest herbs and tree seedlings rooted themselves
in the duff layer. When earthworms invaded, the plants were
essentially uprooted.
But how will
forests adjust to the invasion of "nature's plow"?
Which plant populations will recover and why? How will nonnative
earthworms affect the productivity of northern hardwood forests?
What are the implications of nonnative earthworms for forest
conservation efforts? Many forest managers are asking these
questions. I hope my PhD research provides useful answers.
Now it is back to the
nitty-gritty of research work.
It's time to pick up my field equipment and field assistant,
and head out to harvest samples from a field experiment.
The work and play in the Porcupine Lake Wilderness Area
seems so far away.
To learn more about these and many other changes caused by
nonnative earthworms, visit the Minnesota Worm Watch website:
www.nrri.umn.edu/worms
###
