Stages of earthworm invasion

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Lee Frelich
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Stages of earthworm invasion

Post by Lee Frelich » Fri Jun 17, 2011 12:43 pm

ENTS:

The pictures from my May field trip to the Porcupine Mountains can be further used to illustrate the stages of European earthworm invasion in sugar maple forest. Several of us at the University of MN (Scott Loss, Ryan Hueffmeier, myself, George Host, Gerry Sjerven, and Cindy Hale) have also submitted a manuscript for publication in a peer-reviewed journal on rapid visual assessment of earthworm invasion.

The landscape of the Porcupine Mountains is very large and has places with all stages of invasion (photo by G. Schlaghamserky).
George 5.jpg
Stage 1 is no earthworms. The leaf litter is flat (after several months cover by snow), the leaves are stuck together and bleached to a light color, reflecting no earthworm movement through the leaves (photos G. Schlaghamersky and Kalev Jogiste):
George 2.jpg
Kalev 2.jpg
Notice that this is visible even at the stand level (photo by Kristi Teppo):
Kristi 2.jpg
Compare this with pictures of stage 2, with thick leaf litter, with all three layers still present (L = fresh litter, F = fragmented litter and H = humus), but with the small earthworm Dendrobaena octeadra moving through, so that the surface of the litter has a different color and texture (Photos by Kristi Teppo):
Kristi 3.jpg
Kristi 4.jpg
Stage 2 is hard to differentiate from stage 3 in spring, but here are two pictures of stage 3, which actually has a thin F layer underneath the fresh litter, and notice how loose the leaf litter is. Lumbricus rubellus (leaf worm) and Aporrectodea species (angleworms) are present (photos by G. Schlaghamserky and Kajar Koster):
George 4.jpg
Kajar 1.jpg
Stage 4 has patchy invasion of Lumbricus terrestris (nightcrawler), but is still dominated by L. rubellus and Aporrectodea. Here the F layer is absent in some areas, so that fresh leaf litter is sitting on top of mineral soil, but there are still some fragmented patches of F layer underneath the fresh litter. Note that mineral soil is visible in the lower left, and that most leaves are standing at angles at various angles from 40 degrees to vertical:
Kalev 1.jpg
Stage 5 of invasion (terminal stage) is dominated by nightcrawlers, and only fresh leaf litter that has not yet been eaten is present, and often it is in bunches, since the nightcrawlers have pulled leaves they want to eat partially into their burrows. In the second photo, which was taken in late summer on a different field trip, basswood and maple leaves have been eaten and oak leaves remain, since worms eat leaves in order of palatability (Photos by Kristi Teppo and Paul Ojanen):
Kristi 1.jpg
Ojanen 1.jpg
Finally, three profiles from soil cores illustrate stages 2, 3, and 5 of invasion (Photos by G. Schlaghamersky):

Stage 2, with a few Dendrobaena and thick fresh litter at right, fragmented litter (F layer, brown with some brighter flecks) and humus (H layer, black) underneath the fresh litter, on top of beige mineral soil at left (8 inch deep core):
Stage 2.jpg
Stage 3, a thin fresh litter layer at right, very thin almost invisible F layer, and mineral soil of the A horizon starting to change color at left. Leaf worms and angleworms are present.
Stage 3.jpg
And stage 5, litter on top at right is a middens of a nightcrawler (remains of leaves the worm has eaten). The F and H layers are gone, and the mineral A horizon of the soil has turned black, and looks like what soils scientists call a plow layer, which occupies most of the core.
Stage 5.jpg
So, that's the sequence of invasion--hope you find it interesting.

Lee

Joe

Re: Stages of earthworm invasion

Post by Joe » Fri Jun 17, 2011 1:41 pm

Lee, I'm confused about this- are there no native earthworms in North America?
Joe

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Lee Frelich
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Re: Stages of earthworm invasion

Post by Lee Frelich » Fri Jun 17, 2011 2:33 pm

Joe:

There are native earthworms in the southeastern U.S. (south of a line from Des Moines to Boston) and in the Pacific Northwest. Generally, New England has few or no native earthworms, being at the extreme north edge of the range for native earthworms. However, even when native earthworms are present, the invasive worms can still cause extensive damage (making forests more sensitive to drought, causing more runoff when it rains, disrupting nutrient cycles, water quality problems, loss of native plants and fungi, and increasing the effectiveness of deer as herbivores that eat tee regeneration), because they reach higher numbers as invasives than on their native continent and often represent different functional groups than native worms, so they still change the soil, as recent studies from the Great Smoky Mountains show.

Lee

Joe

Re: Stages of earthworm invasion

Post by Joe » Fri Jun 17, 2011 4:50 pm

Lee Frelich wrote:Joe:

There are native earthworms in the southeastern U.S. (south of a line from Des Moines to Boston) and in the Pacific Northwest. Generally, New England has few or no native earthworms, being at the extreme north edge of the range for native earthworms. However, even when native earthworms are present, the invasive worms can still cause extensive damage (making forests more sensitive to drought, causing more runoff when it rains, disrupting nutrient cycles, water quality problems, loss of native plants and fungi, and increasing the effectiveness of deer as herbivores that eat tee regeneration), because they reach higher numbers as invasives than on their native continent and often represent different functional groups than native worms, so they still change the soil, as recent studies from the Great Smoky Mountains show.

Lee
Lee, so all those earthworms I've grown up with were not native (in Berkshire County of western Mass. with very rich soils on limestone)? I never think of looking for them in the forest so I never even give a thought as to whether they're there or not- to me, the worms were in gardens. I used to sometimes help my father dig in the garden- the worms were huge.

Unfortunately, where I live now I have no worms. It's in north central Mass. on glacial outwash plane- heck, the soil is nothing but gravel and sand, made even worse because most of this 'hood was ripped up for a gravel pit before turned into a 'hood and they didn't bother to restore the soil very well. No worms but the ground is loaded with tiny ants. They're in the garden and in the lawn. The garden seems mostly OK, but nothing like the lawn my family had on that rich soil on limestone bedrock- I think the ants hold back some of the garden growth and they definitely don't help the lawn, which is mostly scruffy and dries out quick in summer heat. I'd much rather have earthworms than ants!
Joe

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KoutaR
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Re: Stages of earthworm invasion

Post by KoutaR » Sat Jun 18, 2011 2:09 am

Lee,

Your post is highly interesting, again. Are there native earthworms in the prairies?

Kouta

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jamesrobertsmith
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Re: Stages of earthworm invasion

Post by jamesrobertsmith » Sat Jun 18, 2011 5:37 pm

I've been in a few places recently after winter where the forest floor was all flattened as in your earlier photos. Can I assume that these areas are devoid of earthworms? One spot was in the Black Mountains here in NC, the other in WV on a bushwhack in Blackwater Falls State Park. Both places had experienced recent heavy snowfalls that had melted off. I'd never seen forest floors that were flattened like that--so what I will assume is that I'd never hiked in forests that had not only been squashed under several feet of snow, but which also didn't have earthworms.

Any way to control the populations of invasive earthworms?

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Lee Frelich
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Re: Stages of earthworm invasion

Post by Lee Frelich » Sat Jun 18, 2011 9:49 pm

Joe:

That's right in western MA its unlikely that there would be native earthworms except in a few very sheltered places, they certainly wouldn't be all over the landscape. There are a number invasion fronts of earthworms in MA, such as along the creek right outside Bob Leverett's house.

Kouta:

Yes, in places like southern Iowa, central Illinois, and eastern Kansas there are native earthworms. They are limited by lack of soil moisture going west, and by cold going north. European earthworms have invaded prairies in central North America, but there have been relatively few studies of their effects in prairies. European earthworms can tolerate much colder climates than North American natives, so they occur in places in Canada that had permafrost a few years ago (and of course they are native to Sweden and Finland, so it is expected that they should be able to withstand more extreme climates than our native worms).

James:
It is a likely possibility that those area with flat leaf litter have no or very few earthworms. Earthworms really churn up the duff when they move through it.

Lee

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Larry Tucei
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Re: Stages of earthworm invasion

Post by Larry Tucei » Mon Jun 20, 2011 12:54 pm

Lee, Very interesting stuff. What are some of the negative effects of the invasive worms? I don't think many of us really noticed the difference in the leaf mass. I have seen in places where leaf litter was disturbed by turkeys, deer, hogs, etc., but didn't think about the earthworms. I will pay more attention when I'm back in the Central Ms. and northern Wisconsin Forest this fall. Larry

Joe

Re: Stages of earthworm invasion

Post by Joe » Mon Jun 20, 2011 1:28 pm

by the way, and I suppose I could look it up, but why are there so few native earthworms in North Amerca? I should think an ancient and primitive species like earthworms should be found in all temperate climates- and, if they are able to spread through as they have, I'd think that perhaps they were here once but driven out by the glaciers and they're just slow at coming back?
Joe

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Lee Frelich
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Re: Stages of earthworm invasion

Post by Lee Frelich » Tue Jun 21, 2011 2:56 pm

Larry and Joe:

Earthworms are the most important terrestrial invasive species group in the world. In temperate forests, their impacts include warmer, drier and more nutrient poor soils. The leaf litter that earthworms remove insulates the soil during summer, keeping it cool; N and P leach out of the soil when worms invade, and soils are compacted so that more rain runs off. Fungal communities are disrupted, including mycorrhizas that sugar maple associates with, as well as fungi that orchids need to germinate. Seedbed conditions are changed from leaf litter to mineral soils--this changes the species of plants that can successfully germinate. This change in leaf litter, nutrient status and water leads to loss of native plant species (trilliums, violets, spikenard, etc.) as well as less successful tree regeneration (sugar maple, red oak). The effect of deer grazing on native plants and tree seedlings is enhanced. Invasive plant species that coevolved with the worms on their native continent are facilitated by exotic earthworms--garlic mustard, stiltgrass, buckthorn, etc.). Finally, wildlife habitat is changed, with for example, negative effects on ovenbirds and salamanders.

The North American earthworm species are just not as tolerant of climatic extremes as European ones, and they are not as aggressive either. Apparently European earthworms also reach higher densities here than in Europe, which is common for invasive species, so they are able to displace native earthworm species in human dominated ecosystems.

Have to finish now--the tornado sirens just went off.

Lee

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