Forest decline, Earthworms, and seedling growth   Lee Frelich
  Sep 11, 2005 12:32 PDT 

Wood-Rill Natural Area is a remnant of old-growth sugar maple, basswood,
red and white oak forest near Minneapolis that has been hit particularly
hard by the forest decline syndrome caused by European earthworms, European slugs, and overabundance of deer. ...

(full report)

European Earthworms   Phil
  Sep 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. Could you
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 invasive
species which is compounding is destruction?



Re: European Earthworms   Lee Frelich
  Sep 13, 2005 17:23 PDT 


There are 8 species of European earthworms invading forest in the
northeastern U.S. Some of them, such as Dendrobaena octeadra, an epigeic
species that lives in the duff, but does not eat the duff, have no negative
impacts that we can see.

Several other species such as Apporectodea (3 species, known as angle
worms), Octolasion tyrtaeum, and Dendrodrilus rubidus, are endogeic (they
live in the soil), and they have some impact on the forest. They have
lateral branching burrows.

Then there is the genus Lumbricus, with two species. L. rubellus (known as
the leaf worm, and epi-endogeic species) which completely changes the
forest floor, by eating the duff, thus changing the type of seedbed, and
the species of plants that can germinate there in the future. It also kills
the standing crop of tree seedlings, ferns and wildflowers, in some cases
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 species is

Finally there is L. terrestris, the night crawler, which is in the anecic
functional group, meaning that it lives in vertical burrows, and eat fresh
litter. They prevent the forest floor from being reestablished by eating
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 than the
earthworms, so that the soil becomes hard and dry when the worms invade.

What this all amounts to is a re-engineering of the entire ecosystem. Less
water infiltrates the soils, nutrients are less available, and the seedbed
is different. Therefore, the forest type will change, or even be converted
to savanna, as is happening to old growth hemlock in some parts of Sylvania.

A large scientific literature is developing on this forest decline syndrome
as we have started to call it. The really unique thing about invasive
species that are ecosystem engineers is that they know no ownership
boundaries, and can thus destroy remaining 'protected' old growth.

Thursday and Friday I will be a guest for the annual meeting of the
governing board of the Wilderness Society, and also some high Forest
Service officials like Sally Collins, the Associate Chief of the Forest
Service, and I am sure they will be stunned by what I tell them. We are
going to have to totally rethink how we manage the forest in light of these
types of invaders.

RE: European Earthworms   Gary A. Beluzo
  Sep 13, 2005 17:59 PDT 


Any idea how far north the European earthworm has advanced in New England?

RE: European Earthworms
  Sep 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.

RE: European Earthworms   Lee Frelich
  Sep 13, 2005 18:44 PDT 


There are reports of European earthworms in forests of Quebec near
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 start at
lakeshores and rivers where people fish, and leave behind live bait, which
is usually European earthworms. Thus, there are many invasion fronts that
have progressed various distances from lakes and rivers.

At least the Asian earthworms aren't used as bait. They are used in
compost, so they are being distributed around second homes being built in
the woods, but not to remote areas like European earthworms used as fishing
bait. If you think the European earthworms are aggressive, you should see
the Asian worms.


RE: European Earthworms   Lee Frelich
  Sep 13, 2005 18:49 PDT 


In addition to European earthworms, I think SE PA probably also has the
Asian worms, which are more cold sensitive than European ones, and may not
be able to colonize northern areas. SE PA also has native earthworms, but
I doubt that they reach the abundance of the exotic ones.

Earthworms definitely don't like low pH--but if you make all the soil low
pH you will re-engineer the ecosystem just as much as the earthworms would.


Re: European Earthworms   Dean Hedin
  Sep 13, 2005 20:15 PDT 

You would think that there would be some natural, indigenous control via
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 fern species
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 bigger concern)?
RE: European Earthworms
  Sep 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.

RE: European Earthworms
  Sep 14, 2005 06:17 PDT 


We know almost nothing about native worms near the northern edge of their
range, but I suspect that they become very spotty in distribution,
probably concentrating in riparian areas near the northern edge. I grew up
in an area, southeastern WI, that, like most of PA, is shown within the
range of native earthworms on most maps, yet I never saw anything but
Lumbricus and Apporectodea in the 30 years I lived there.

Regarding bird predators, they cannot control earthworm populations.
Because of the territoriality of birds, they cannot ever get dense enough
to eat all of the worms. Also, our earthworm removal experiments show that
about 50% of all earthworms can be removed repeatedly (every month)
without a noticiable reduction in population. Cocoons in the soil hatch
and the worms grow up quickly to replace the removed worms, whereas they
hatch but die if competing with adult worms. This excess capacity ensures
that predatory control is unlikely. Of course, thats why any invasive
species--plant or animal--becomes invasive, because there is no predatory

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 other non
target native species, so at this point its introduction is not being
considered a viable option.

Re: European Earthworms   Michele Wilson
  Sep 14, 2005 08:25 PDT 

Thanks, Lee;
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 one of
them. Perhaps I'll have to add doing soil testing for invasive species of
worms to the management practices sections of management plans I prepare.
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 any
particular state that any of us work in might already be invaded?
Re: European Earthworms   Lee Frelich
  Sep 14, 2005 11:21 PDT 


Reports by county for some states are available in a scientific publication
called Megadrilogica. It is hard to get. Of the 500,000 scientific
journals published in the world it is probably near the bottom. Very few
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 in the
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 back.