From ORNL Reporter, June 2001

Understanding the invader

ORR researchers seek to understand Microstegium and other exotic plant pests

Just about everyone in the southern United States is familiar with the infamous "miracle vine" kudzu. This pervasive plant blankets the landscape with such haste that southerners have claimed to close their windows at night just to keep the kudzu out.

The profusion of kudzu might make it seem like a native plant to the area, but it is actually a foreign species—brought from Japan early last century to control erosion.

Another plant from Japan and its surrounding regions has enjoyed widespread dominion in East Tennessee and the entire eastern United States: Microstegium vimineum, also known as Japanese stilt grass or wire grass.

Microstegium is an annual grass with tall stems and sparse, alternating leaves. It is not nearly as conspicuous as kudzu, but it could present greater ecological concerns. In fact, it has become one of the major environmental management problems in the Great Smoky Mountains National Park.

There are various claims regarding the evils of non-native grass species like Microstegium, but very little definitive data have been gathered to support these assertions. This is why Michael Huston of ORNL's Environmental Sciences Division has teamed up with Patrice Cole from the University of Tennessee to shed some light on this grass. Patrice is a doctoral student working with Jake Weltzin in UT's Department of Ecology and Evolutionary Biology.

The invasive grass Microstegium vimineum growing along the side of an unpaved road
This bucolic lane on the ORR is actually an invasion site. The tall roadside grass is Microstegium vimineum.

At this point, understanding is the main research goal, not eradication. "We are trying to understand its habitat requirements and how it responds to variations in environmental conditions," says Patrice. "We need to know these fundamental things before we can develop any kind of control strategies."

One major concern is the crowding-out of native species. Microstegium usually grows sparsely along roadsides or trails, where it poses little threat. However, it has also been observed in large patches covering several acres of land. "When you see it growing in a virtual mono-culture, it's hard to imagine that it's not displacing natives, because surely something would be growing there if it weren't," says Patrice.

Microstegium grows abundantly throughout the Oak Ridge Reservation, but it is present in unusual patterns. "In some places it is very dense; some places it is sparse; some places you don't see it at all," says Patrice. "We are looking for any particular patterns that might help us understand where we would expect to find it and why we don't see it everywhere. The natural question is: "Why isn't it where it isn't?"

The main thrust of the experimentation revolves around a theory referred to as the "light/water trade-off hypothesis." It suggests that plants can't simultaneously adapt to low-moisture and low-light conditions. They are either drought-tolerant or shade-tolerant, but they can't be both. Therefore, plants grown in low light should do better when supplied with excess water, and vice versa. Two experiments—one in the field and one in a greenhouse—have been designed to test this hypothesis.

How will knowledge of this interaction between light and water aid in the understanding and control of Microstegium? "It has implications for whether the Microstegium is going to be there forever," says Michael. "A lot of the places we see Microstegium now are places that have been disturbed fairly recently. But, as natural forest succession proceeds you are going to get a deeper and deeper shade, which is likely to just eliminate the Microstegium."

This process has also been observed in other weeds. "This whole area used to be farm fields," says Michael, referring to the ORR. "We had all the weeds you could typically find in fields, but they aren't there now. That's because the forest has come up and shaded them out."

For now, it appears that both kudzu and Microstegium are here to stay—so why not make the most of them? Some resourceful people have been putting the kudzu vine to good use. It has been employed in making baskets, paper, jelly, syrup and even kudzu quiche. In fact, kudzu has been a common cooking ingredient in China and Japan for hundreds of years.

So what about Microstegium?

"One apparent use of Microstegium is as a packing material for chinaware," says Patrice. The first discovery of Microstegium in North America was actually made in Knoxville, in 1918. One theory proposes that someone received a shipment of china that was packed in the wiry grass, then they just tossed the seed-bearing packing out the back door.

Patrice contemplates the potential of Microstegium in today's environmentally conscious marketplace: "Maybe it will replace Styrofoam peanuts. We could market it as a biodegradable, totally organic packing material. But, you would want to make sure that it's seed-free, because we don't want to facilitate its propagation. It is getting around quite well on its own."—Jason Gorss

University of Tennessee student Jason Gorss is working at ORNL this summer on a science-writing internship in the Office of Communications and Community Outreach.

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