Worms can be too much of a good thing

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Capital News Service
LANSING — Wriggly soil-dwellers may not have the bad rep of some of their invasive counterparts but they do have the power to change entire ecosystems.
“It’s ingrained into our education that earthworms are good,” said Chuck Elzinga, assistant professor of biology at Michigan State University. “But the more earthworms you have, the worse it is.”
Now a recent study has found that an abundance of earthworms decreases the small plant matter scattered on the forest floor. By eating away at what scientists call “fine root biomass,” worms can significantly change the forest.
The good news is that when worms decompose matter and convert it into carbon dioxide, the levels of the greenhouse gas will not necessarily increase with more worms in a given area. For now, worms are not a serious threat to climate change.
Charles Darwin was fascinated by earthworms and hailed them as one of the most influential animals in the history of the world.
Worms start a bottom-up chain reaction that can bring about fundamental environmental changes, according to Elzinga.
They affect what plants are able to root and grow in the soil. The kinds of plants that grow affect which species of animals can live in a forest.
The process starts when worms eat organic matter like leaves at the top of the soil. They break down the nutrients in the material to feed the surrounding trees and plants, but all that activity is too much of a good thing.
“They decompose plant material very rapidly,” said Elzinga, who wasn’t part of the study team. “It’s so rapid that the plant life can’t take it up. Those nutrients are lost or taken up by other organisms that aren’t trees.”
Sugar maples, common to the Great Lakes states and provinces and the East Coast, are especially vulnerable to worms. That’s because their seedlings can’t get sufficient nutrition.
Worms also release carbon dioxide into the soil and ultimately into the atmosphere in a process called respiration. But the new study from Trent University in Ontario discovered that having more earthworms in a given area doesn’t necessarily equate to more soil carbon dioxide emissions.
The scientists involved in the experiment tested two plots of land near Catchacoma, Ontario, over the course of a year. One plot had invasive earthworms while the other didn’t. The researchers found no significant difference in total soil respiration, the soil’s capacity to support life. That conclusion contradicted previous laboratory studies.
Shaun Watmough, assistant professor in the ecosystems research group at Trent University, said that’s because the lab studies didn’t take enough environmental variables into account.
“In nature there are a lot of things going on,” said Watmough, a co-author of the study published in Ecosystems. “You’ve gotta try and take into account those other processes.”
The study found that plant biomass was significantly lower at the site with invasive worms.
Getting rid of worms is tricky. They’re slow-moving but people can spread them.
That’s how they arrived in North America.
The continent 10,000 years ago was inhospitable for worms. But once the glaciers retreated, the landscape was primed for earthworms. It was the perfect storm when Europeans colonized the continent and brought plant material that contained worms.
“There are even more recent invasions of worms,” MSU’s Elzinga said. “Now we have earthworms from Asia, other parts of the world who have come the same route, by humans.”
Chloe Kiple writes for Great Lakes Echo.

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