Asian worms chomping through forest floors

Species sets stage for appearance of Japanese stilt grass

October 29, 2001|By Sandy Bauers | Sandy Bauers,KNIGHT RIDDER/TRIBUNE

PHILADELPIHA - If only there hadn't been an Ice Age, Dennis Burton might not be in such a fix today.

But there was, wreaking havoc among the nation's worms. So here Burton was, turning over logs in the woods of the Schuylkill Center for Environmental Education in Roxborough, Pa., and scrabbling in the dirt in search of wigglers.

"Oh, yeah," said the director of land restoration, grabbing a little brown worm. Captive in his hand, it flipped and thrashed. "That's a monster!" he said.

Just as he suspected, it was also an interloper.

Burton's worm was of an Asian species that he and others say is chomping through the leaves on forest floors in the northern United States at an alarming rate.

Here, in what Burton calls the Schuylkill Center's "invasion zone," their vigorous digestive processes have left several inches of "casts" - worm droppings - atop the soil and also have set the horticultural stage for a takeover by Japanese stilt grass, one of the vigorous upstarts crowding out native plant species.

The way he sees it, this worm "could be as destructive to the forest as the white-tailed deer."

The worm warrior

Burton, of West Mount Airy, Pa., never intended to be a worm warrior. He was an English major who became a horticulturist partly because he liked the poetic ring of the Latin names, "and the next thing I know, I'm dealing with worms."

He found out that, astounding as it may seem, virtually all the country's northern worms were wiped out in the Ice Age.

"Large areas of North America were worm-free," confirmed Sam James, a professor of life sciences at Maharishi University of Management in Fairfield, Iowa, and one of the country's few experts on worms.

Southern worms survived. But worms, it seems, aren't much in the migration department. They can squirm only so far, and 10 meters a year is considered a pretty good clip.

So the turf was ripe starting in the 1600s, when alien worms made their entrance with human immigrants, hitchhiking in the soil of plants they brought.

Now, we've got earthworms in the United States from Africa, South America, Asia and Europe.

Many of them are beneficial, James said - a boon to gardeners and anglers and robins.

A few, however, are not. And that includes the particular species Burton has found at the Schuylkill Center. Others have been found in Fairmount Park.

There, the woods have what they love: leaves.

Writhing soil

"Last year, when I pulled the leaf litter back in any given area, the soil literally writhed," Burton said. "It was like a science-fiction movie."

Burton and James believe the worms are probably in a lot of forest systems, but people just haven't noticed. Until very recently, "nobody cared about studying earthworms," James said. And how many people go rooting about in the woods looking for worms?

One who does is Anne Bockarie, a biology professor at Philadelphia University, who has been coming to the center - and bringing her students - to study the effects.

As it happens, the forest floor is a complex world. The so-called duff layer is made up of several inches of leaves that take years to decompose, courtesy of zillions of fungi and microbes. Meanwhile, the duff keeps the soil from eroding and baking in the sun. Nutrients ooze back into the system.

This organic layer "is critical to the survival of the plants," Bockarie said, and if the gluttonous invading worms gobble it all in a single year, "there's not enough food for everyone else."

Burton likened them to runaway miniature rototillers. In their wake, the upper layer of soil actually isn't soil. It's crumbly, porous worm casts that don't hold water and that have an entirely different chemistry.

Burton thinks the region's shallow-rooted spring flowers - trilliums, bellworts and such - may decline or even disappear in areas the worms invade.

James said it has happened in other places, including some forests in Minnesota. "It's somewhat interactive," he said, "with deer" - an animal this region has more than enough of. "Maybe neither the worms nor the deer alone will do it, but the combination is deadly."

Some of Bockarie's students are mapping out small squares, dousing the area with a mustard solution that the worms apparently find mildly irritating and counting worms as they surface.

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