Hold the front page for:
Exhibit A: the Ecol. Soc. America paper abstract
http://199.245.200.35/esa-abstracts/abstracts/CIN-3-48-6.html
Impacts of invading European earthworms on understory plant communities in
previously worm-free hardwood forests of Minnesota. HALE, C.M.,
L.E.FRELICH and P.B.REICH
Abstract: During the last few decades, European earthworm species have
been invading hardwood forest ecosystems in the northern tier of states in
the U.S. These hardwood forests have developed since the last glaciation in
the absence of native earthworms, and many stands historically had thick
forest floor layers, that served as rooting medium for many species of
forest herbs and tree seedlings. Leading edges of earthworm invasion have
been identified in the Chippewa National Forest of northern Minnesota and
a pilot study was conducted. Our objectives were to elucidate the rates and
patterns of change in earthworm populations, forest floor and upper soil
horizons, herbaceous understory vegetation and seedling demography
related to the visible leading edge of earthworm invasion in previously worm-
free hardwood forests. A 30 by 150m grid of nested sample plots (45
sample points) was established perpendicular to the visible leading edge in
4 northern hardwood sites. Forest floor thickness, herbaceous plant
diversity and tree seedling density decreased dramatically with increasing
earthworm biomass. Successive appearance of 5 different earthworm
species and replacement of the E horizon by an A horizon were also
associated with the visible leading edge. Heavily impacted stands have
been observed with only one species of native herb and virtually no tree
seedlings remaining. Therefore, concerns have been raised about the
widespread loss of native forest plant species and the stability of hardwood-
forest ecosystems.
Exhibit B: The news story
http://www.academicpress.com/inscight/08082000/grapha.htm
SNOWBIRD, UTAH -- Exotic earthworm species are wreaking ecological
havoc in the northern Great Lakes region, researchers warned here on 7
August at the annual meeting of the Ecological Society of America. In the
most heavily affected areas, the invading worms have devastated plants
and turned a forest floor once carpeted with leaf litter into bare soil.
Some 18,000 years ago, thick ice sheets killed all the native earthworms in
the northern half of North America. Recolonization by native worms has
been slow, and there are still no native species in the northern part of the
United States and Canada. When European colonists arrived in the East
toting plants and seeds, Old World earthworms came along, too--as many
as 14 species. Now ensconced in soils around cities and farms, the worms
are on the march. And once again, humans--by transporting worms for fish
bait and dumping out the extras, for example--are helping them spread.
To see what vanishes when worms crawl in, Cindy Hale, a forest ecologist
at the University of Minnesota, Twin Cities, and her colleagues studied the
advancing worm front in the Chippewa National Forest in Minnesota.
During the last 2 years, the frontier of the worm invasion moved about 10
meters into the forest. The forest floor, in turn, lost about 75% of its plant
cover. The invaded areas had only one or two species of forest floor plants,
while 150 meters away, the worm- free zones had more than 10. And tree
seedlings, usually found in densities of 100 per square meter in the worm-
free zone, were almost entirely absent. It's not entirely clear yet how the
worms disrupt the ecosystem, but the long-term results could be dramatic,
says Hale: "A worst-case scenario is the total extirpation of a whole suite of
understory plants, many of which are our most beloved spring flowers,
including trilliums and spring beauties."
The findings surprised some scientists. "I've never seen somebody link a
decrease in biodiversity to invasion by earthworms," says Mark Hunter, an
ecologist from the University of Georgia, Athens. Nor have many other
ecologists, says Hale. When she asks forest ecologists if there are worms
in the soil they study, she says, "nobody knows!" --MARI N. JENSEN
--
Geoff Read <g.read at niwa.cri.nz>
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