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I was shocked to learn that there were few native worms in the glaciated portion of North America. I use worms indoors to compost paper and kitchen scraps. I don't think there is much chance of transfer as my garden is on the roof of an apartment. I was still surprised that my worms are essentially invaders in some parts of this country.

Thinking about all of this lead me to look up the damage done by non-native worms in North America. They have an impact on plants that once relied on the matted leaves on the forest floor. So, they can lead to more barren undergrowth. The native worms are not good at competing for some reason.

And I thought all worms were beneficial!

Still, before the most recent glaciers there were worms in these regions. So, why isn't this like turning the clock way back? In the end, after the glacier's impact fades, shouldn't there be a lot of worms again some day?

I guess sudden change is hardly ever desirable. But I'm very confused about how to identify an invaded ecosystem. Is it just based on what humans notice? Has anyone tried to make the concept more objective?

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    $\begingroup$ I don't have a specific answer but recent ecosystem research questions the existence of a steady-state ecosystem as a natural trait. Ecosystems are constantly changing in response to changes in environment and competition among species. I have a personal theory that people think that things are supposed to be the way they were when they were 14 years old. But our values are somewhat arbitrary. It is easier to identify non-indigenous species than to identify the shifts in natives in response to human and other stresses. You do make a good point about sudden change not being desirable. $\endgroup$ – haresfur Apr 20 '15 at 2:24
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    $\begingroup$ "In the end, after the glacier's impact fades, shouldn't there be a lot of worms again some day?" No. Whether worms develop again depends on a lot of chance factors. Evolution has no direction. $\endgroup$ – Jan Doggen Apr 20 '15 at 11:29
  • $\begingroup$ l doubt the worms would need evolve, they could just migrate through the soil from the south. You are right it could take any direction I was thinking a bit more short term. $\endgroup$ – futurebird Apr 20 '15 at 12:39
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The native worms are not good at competing for some reason.

There's a reason for that. There are no native earthworms in New York.

Still, before the most recent glaciers there were worms in these regions.

North America has been hammered by multiple glaciations for the last two million years. It wasn't just the areas covered by ice that lost their earthworms. The northern forest, or taiga extended to the Gulf Coast at the peak of the last glaciation. You have to drive to Ontario to see the taiga now. The Great Plains were the mammoth steppe, very cold and very dry. Most of the US is depleted of native earthworms.

Invasive earthworms are your enemy if you like maple syrup. Sugar maples take a couple of years to germinate, and only need a nice pile of duff (leaf detritus that hasn't been consumed by earthworms) in which to do so.

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