decline, Earthworms, and seedling growth
11, 2005 12:32 PDT
Wood-Rill Natural Area is a remnant of old-growth sugar maple,
red and white oak forest near Minneapolis that has been hit
hard by the forest decline syndrome caused by European
slugs, and overabundance of deer. ...
13, 2005 08:30 PDT
I've talked a little with
Gary and seen a few posts mentioning the
European earthworm. What I'm curious about is the worm itself.
enlighten me on why this species is having such a negative
impact on our
forests? Also, I'll assume that the European earthworm is an
species which is compounding is destruction?
13, 2005 17:23 PDT
There are 8 species of European earthworms invading forest in
northeastern U.S. Some of them, such as Dendrobaena octeadra, an
species that lives in the duff, but does not eat the duff, have
impacts that we can see.
Several other species such as Apporectodea (3 species, known as
worms), Octolasion tyrtaeum, and Dendrodrilus rubidus, are
live in the soil), and they have some impact on the forest. They
lateral branching burrows.
Then there is the genus Lumbricus, with two species. L. rubellus
the leaf worm, and epi-endogeic species) which completely
forest floor, by eating the duff, thus changing the type of
the species of plants that can germinate there in the future. It
the standing crop of tree seedlings, ferns and wildflowers, in
no seed source is left. The duff is consumed within a few days
in any one
spot. I often see exposed fine root systems of plants when this
Finally there is L. terrestris, the night crawler, which is in
functional group, meaning that it lives in vertical burrows, and
litter. They prevent the forest floor from being reestablished
all of the litter that falls each year.
All of the earthworms cement soil particles together, and
replace a group
of native insects that are more efficient at aerating the soil
earthworms, so that the soil becomes hard and dry when the worms
What this all amounts to is a re-engineering of the entire
water infiltrates the soils, nutrients are less available, and
is different. Therefore, the forest type will change, or even be
to savanna, as is happening to old growth hemlock in some parts
A large scientific literature is developing on this forest
as we have started to call it. The really unique thing about
species that are ecosystem engineers is that they know no
boundaries, and can thus destroy remaining 'protected' old
Thursday and Friday I will be a guest for the annual meeting of
governing board of the Wilderness Society, and also some high
Service officials like Sally Collins, the Associate Chief of the
Service, and I am sure they will be stunned by what I tell them.
going to have to totally rethink how we manage the forest in
light of these
types of invaders.
13, 2005 17:59 PDT
Any idea how far north the European earthworm has advanced in
13, 2005 18:34 PDT
We have them here in Se Pa. There are two kinds that I know of.
The one that lives on the surface and eats all the duff, and the
one that makes the vertical tunnels. Sometimes when I walk in
the woods, it feels like the ground is moving. That's because it
is, from all the damn worms!! I was told that they were
accidentally imported in colonial times in the ballast of ships
that was unloaded onto the shores so the ships could be filled
with product. The Schuylkill Center for Education has been
experimenting in controlling the worms, so far they don't like
sulfur or hot pepper! Maybe it is a PH thing?? Who knows.
13, 2005 18:44 PDT
There are reports of European earthworms in forests of Quebec
Montreal, where they have caused dieback of sugar maple,
apparently due to
disruption of mycorrhizae leading to Phosphorus deficiency.
European earthworms are likely present through all of New
England, but are
probably spotty in distribution, since they usually get their
lakeshores and rivers where people fish, and leave behind live
is usually European earthworms. Thus, there are many invasion
have progressed various distances from lakes and rivers.
At least the Asian earthworms aren't used as bait. They are used
compost, so they are being distributed around second homes being
the woods, but not to remote areas like European earthworms used
bait. If you think the European earthworms are aggressive, you
the Asian worms.
13, 2005 18:49 PDT
In addition to European earthworms, I think SE PA probably also
Asian worms, which are more cold sensitive than European ones,
and may not
be able to colonize northern areas. SE PA also has native
I doubt that they reach the abundance of the exotic ones.
Earthworms definitely don't like low pH--but if you make all the
pH you will re-engineer the ecosystem just as much as the
13, 2005 20:15 PDT
You would think that there would be some natural, indigenous
predation for these worms that
operate in the "duff". If they are close to the
surface then they should be
easy pickings for rodents, birds etc..
I don't know, I've read a few online articles about the rare
being threatened in Minnesota, but I don't find the evidence
convincing enough to say the worm is the direct cause. Is
is not possible
that some of the surface predators are lacking (which is a
14, 2005 04:13 PDT
I thought the native earthworms were pushed down around
Baltimore with the last glacial activity? How fast to they
migrate I wonder? I didn't thimk they were back up here yet. One
good thing is, I see alot more robins in the woods now. I can
only imagine that certain species of birds that eat worms will
grow in population proportionately with the worms.
14, 2005 06:17 PDT
We know almost nothing about native worms near the northern edge
range, but I suspect that they become very spotty in
probably concentrating in riparian areas near the northern edge.
I grew up
in an area, southeastern WI, that, like most of PA, is shown
range of native earthworms on most maps, yet I never saw
Lumbricus and Apporectodea in the 30 years I lived there.
Regarding bird predators, they cannot control earthworm
Because of the territoriality of birds, they cannot ever get
to eat all of the worms. Also, our earthworm removal experiments
about 50% of all earthworms can be removed repeatedly (every
without a noticiable reduction in population. Cocoons in the
and the worms grow up quickly to replace the removed worms,
hatch but die if competing with adult worms. This excess
that predatory control is unlikely. Of course, thats why any
species--plant or animal--becomes invasive, because there is no
The New Zealand flatworm evolved to prey on earthworms, and
there is some
talk about introducing it, but it is very aggressive and may eat
target native species, so at this point its introduction is not
considered a viable option.
14, 2005 08:25 PDT
I've been having wormy thoughts as well; I did write down those
two books I
think you mentioned awhile back and was planning to get at least
them. Perhaps I'll have to add doing soil testing for invasive
worms to the management practices sections of management plans I
Do you know if any country-wide general surface (no pun
intended!) study has
been done that would hint at whether or not a particular area of
particular state that any of us work in might already be
14, 2005 11:21 PDT
Reports by county for some states are available in a scientific
called Megadrilogica. It is hard to get. Of the 500,000
journals published in the world it is probably near the bottom.
university libraries subscribe unless there is an earthworm
expert on the
faculty that wants it. I have not read any issues other than the
one for MN.
Well, I am off to the Wilderness Society Governing Board meeting
Boundary Waters. There is no e-mail or cell phone service there,
so I will
answer any more earthworm questions on Sunday night when I get