Stages of earthworm invasion

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KoutaR
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Re: Stages of earthworm invasion

Post by KoutaR » Sat Jun 25, 2011 3:45 pm

Lee,

I have an alternative explanation for the inferior cold tolerance of the American earthworms, about opposite to my previous proposal: Could the Americans have LOST their cold tolerance DURING THE HOLOCENE, when they were living in warmer climates and were unable to migrate northwards?

Kouta

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Lee Frelich
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Re: Stages of earthworm invasion

Post by Lee Frelich » Sun Jun 26, 2011 12:13 pm

Kouta:

Its certainly possible that North American earthworms lost their ability to tolerate cold during the Holocene. However, I think the glaciers receded slowly enough that they could have followed the cold climates back to Canada, so although there is no proof, I doubt it.

Regarding Lumbricus terrestris living in the boreal forest of North America, I think they are already doing so. We have forests with high pH and birch and aspen on a permanent basis, because fire frequencies on certain landscapes are very high. Then there are black ash swamps and fens with tamarack, alder, dogwood and willow, which are quite extensive and have pH values of 5-6. Lumbricus could live in all these areas. In 2007, while I was stuck at a certain campsite on Seagull Lake for 2 days as a result of strong winds creating large waves coming from one direction and a 70,000 acre high intensity crown fire coming from the other direction, I even saw L. terrestris in shallow (0.3 m) acid soils (pH 4.5) on top of granite of the Sagananga batholith in jack pine and black spruce forests, but with a few birch and red maple mixed in, and hazel in the understory, so the species can sometimes get along in environments that we don't think it can tolerate. Finally, we now know that L terrestris can eat green leaves of tree seedlings and herbs, which are very abundant on the boreal forest floor.

Lee

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KoutaR
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Re: Stages of earthworm invasion

Post by KoutaR » Sun Jun 26, 2011 4:10 pm

Lee,

Fraxinus swamps are missing in Scandinavia. Also fens with Larix, Alnus, Cornus and Salix are missing, the closest vegetation type being probably forested fen (or bog?) dominated by Picea abies and Betula pubescens. I don't know if Lumbricus lives there. They are of high fertility but spruce lowers pH, of course. But you are right that fire frequencies in boreal forests have been high in the past (often tens of years), and there would probably be enough broadleaf trees on certain landscapes to make the continuing occurrence of Lumbricus possible. So, I think my first proposal is false, and the right one could be your explanation (European and American earthworms were different already before the intensive influence of humans), or my second proposal (American earthworms lost their ability to tolerate cold during the Holocene) as you said it could be possible. In Europe, earthworms could not followe the cold climates without humans!

An another thing: I once had a discussion with Finnish specialists about the question, which would be the most common broadleaf tree species of the world (the highest number of trunks). We all thought the two most common are the Eurasian boreal birch species B. pendula and B. pubescens, followed by Populus tremula or P. tremuloides or B. papyrifera. What do you think - which is more common in America: P. tremuloides or B. papyrifera?

Kouta

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Lee Frelich
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Re: Stages of earthworm invasion

Post by Lee Frelich » Mon Jun 27, 2011 8:49 am

Kouta:

I think the trembling aspen has a bigger range and more individuals than paper birch. Any species that has a range crossing all of Eurasia in the north could be in the running for most abundant tree in the world. For conifers, it has been proposed that black spruce is the most numerous, with a range from Alaska to Quebec. However, such questions can be very hard to answer for sure, even though they are simple questions.

Lee

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KoutaR
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Re: Stages of earthworm invasion

Post by KoutaR » Mon Jun 27, 2011 9:32 am

Lee,

I once read in a book store an American tree book translated to German (don't remember the name). The book proposed the most common conifer would be one of the Eurasian larch species Larix sibirica or L. gmelinii, or white spruce (P. glauca). If Picea obovata is considered a subspecies of P. abies, they together could also be the winner as the range extends over the whole boreal Eurasia. And you suggested black spruce. 4-5 candidates depending the taxonomy. In Eurasia Larix is the northernmost genus and occupies quite a different niche than tamarack in the boreal North America.

Thank you for the earthworm discussion. I learnt something again!

Kouta

Joe

Re: Stages of earthworm invasion

Post by Joe » Thu Mar 01, 2012 9:05 am

Just read an interesting article online:
"Earthworms to Blame for Decline of Ovenbirds in Northern Midwest Forests"

http://www.sciencedaily.com/releases/20 ... 142225.htm
ScienceDaily (Feb. 29, 2012) — A recent decline in ovenbirds (Seiurus aurocapilla), a ground-nesting migratory songbird, in forests in the northern Midwest United States is being linked by scientists to a seemingly unlikely culprit: earthworms.

A new survey conducted in Minnesota's Chippewa National Forest and Wisconsin's Chequamegon-Nicolet National Forest by a research team led by Scott Loss of the University of Minnesota and the Smithsonian Migratory Bird Center has revealed a direct link between the presence of invasive European earthworms (Lumbricus spp.) and reduced numbers of ovenbirds in mixed sugar maple and basswood forests.

The results are detailed in a paper published online in the scientific journal, Landscape Ecology.

European earthworms are invading previously earthworm-free hardwood forests in North America the scientists say, and consuming the rich layer of leaf litter on the forest floor. In turn, herbaceous plants that thrive in thick leaf litter and provide cover for ground-nesting birds are thinning out, replaced by grasses and sedges.

As a result, ovenbird nests are more visible and vulnerable to predators and ovenbirds searching for nesting sites reject these low-cover areas outright. Areas of reduced leaf litter also contain fewer bugs for the ovenbirds to eat, requiring them to establish larger territories, resulting in fewer birds over a given area.

The worms invading northern Midwestern forests (and forests in the northeastern U.S. and Canada) have been in the U.S. since soon after the first European settlers arrived. Loss explains the worms were brought over inadvertently in the ballast of ships, in the root balls of agricultural plants or on purpose for use in gardening. Only now is the leading edge of their continued invasion, caused mainly by logging activities and fishermen dumping their bait, reaching interior wilderness areas such as parts of the study site in the remote forests of Wisconsin and Minnesota.

"Night crawlers [Lumbricus terrestris] and the slightly smaller red worms [also called leaf worms or beaver tails, Lumbricus rubellus], have the most damaging impacts to the soil, litter layer, and plants in forests that were historically earthworm-free," Loss says.

"Everyone has probably heard at one time or another that earthworms have really positive effects in breaking down soil and making it more porous," Loss explains. "This is true in agricultural and garden settings but not in forests in the Midwest which have developed decomposition systems without earth worms."

Because the forested areas of the Midwest U.S. were once covered in glaciers, there are no native earthworm species present in the soil. "These earthworm-free forests developed a slow fungus-based decomposition process characterized by a deep organic litter layer on the forest floor," Loss says.

Earthworms feed on this layer of leaf litter and make it decompose much faster, Loss explains. "As a result, we see the loss of sensitive forest-floor species such as trillium, Solomons seal, sarsaparilla and sugar maple seedlings and a shift in dominance to disturbance-adapted species like Pennsylvania sedge."

One result is reduced nest concealment for the ovenbird and increased predation by squirrel and bird predators.

The researchers found no decline in three other species of ground-nesting birds included in their survey -- the hermit thrush (Catharus guttatus), black-and-white warbler (Mniotilta varia) and veery (Catharus fuscescens) -- nor did they find a correlation between ovenbird decline and invasive worms in other forest types, such as red oak, paper birch and aspen.

"Our results suggest that ovenbird density may decline by as much as 25 percent in maple-basswood forests heavily invaded by invasive earthworms," the researchers conclude. "Maple-basswood forests are among the preferred ovenbird habitats in the region, comprise a considerable portion of the region's woodlands…and are experiencing Lumbricus invasions across most of the northern Midwest."

Previous studies have demonstrated that invasive earthworms also are harmful to other native North American species, such as salamanders.

There is reason for concern that the overall population of ovenbirds could decline, Loss points out. "Ovenbirds migrate to Central America and the Caribbean and back every yea --a trip during which they can fly into buildings and towers or get nabbed by a cat as they rest on the ground--and they also face loss of habitat on their breeding and wintering grounds. Now, here is yet another potential threat to their survival."

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pdbrandt
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Re: Stages of earthworm invasion

Post by pdbrandt » Thu Mar 01, 2012 9:40 pm

I just read up on the impact of invasive earthworms on North American forests. I had no idea that this was a problem. I always thought earthworms were good (and maybe the non-invasive ones still are). If others are interested, I found this article quite informative http://www.sciencenewsforkids.org/2011/ ... ig-impact/

Patrick
Patrick

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Lee Frelich
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Re: Stages of earthworm invasion

Post by Lee Frelich » Sun Mar 04, 2012 2:17 pm

Joe,

Yes, I was aware of this research of earthworm impacts on native birds, in fact I was on Scott Loss's Ph D advisory committee, and he was using some of the research sites I established with Graduate students Cindy Hale and Andy Holdsworth during the early 2000s.

There is also research going on at those sites on soil nutrients such as N and P, soil weathering processes, and effects of earthworms on our native Enchytraied worms (annelids but not considered earthworms). It looks like we discovered 2 or 3 new species of Enchytraieds as well as some species previously only known from Greenland.

Lee

samson'sseed
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Re: Stages of earthworm invasion

Post by samson'sseed » Tue Apr 10, 2012 5:54 pm

The most common earthworm living in my garden in south Richmond County is a small 2 inch long yellow sand worm.

Any idea what species this might be?

There is a familiar more conventional species living in my compost and the area near my septic tank which has richer soil. They look like the red wigglers used for fishbait. I don't know what species that is either.

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Lucas
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Re: Stages of earthworm invasion

Post by Lucas » Wed Dec 03, 2014 7:34 pm

http://vimeo.com/90185609
We travel the Milky way together, trees and men. - John Muir

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