Invasive Meltdown?

Hostile flora pushing out native plants
Death of ash trees by borers might alter Ohio's ecosystem
BY SPENCER HUNT | THE COLUMBUS DISPATCH

OREGON, Ohio - The pair of old ash trees, each about 80 feet tall, are in the final death throes of an attack by emerald ash borers that have infested the Pearson Metropark east of Toledo.

But it's not the trees that Kathleen Knight, a research ecologist with the U.S. Forest Service, is focusing on.

Right now, she is concentrating on a 2-foot-tall garlic mustard plant and a young honeysuckle shrub that are growing thick in a patch of sunlight that would have never hit the forest floor when the ash trees had leaves.

Knight and Ohio State University ecologists fear that the voracious borers will trigger dramatic changes in Ohio's forests - beyond killing millions of ash trees. They also might help invasive plants thrive in sun-drenched areas that were once kept in shade.

About a third of the state - 7.8 million acres - is covered in forest, according to the Ohio Department of Natural Resources. That includes about 191,000 acres of state forests. About 10 percent of the trees are ash.

The chain reaction is what worries experts. If the invasive plants push out shade-loving plants such as wild geraniums, ginger, Virginia creepers and sensitive ferns, they might also make life impossible for the microbes, insects and animals that depend on those native plants.

"There's a term for this," Knight said. "It's called 'invasive meltdown.' "

Knight and John Cardina, an OSU invasive plant ecologist, will spend the next several years measuring the changes emerald ash borers cause in forests. The work will be spread across 155 research plots in Ohio and 114 in southern Michigan.

Their goal is to give state and local government foresters information and strategies to deal with all of the problems associated with the borer.

Previous research has focused on ash trees, including the 254 million threatened in Ohio.

The borers were first discovered near Detroit in 2002, where they had likely hitched a ride from Asia in packing crates.

The insect has since been found in 35 Ohio counties. It is spreading through Pennsylvania, Illinois, Indiana, Maryland and West Virginia.

Ash-borer larvae eat tunnels through the soft wood beneath bark that supply trees with water and nutrients. They can kill adult trees in three to five years.

Invasive plants and shrubs thrive on forest edges, but are kept in check inside by sun-blocking trees, Cardina said.

"Suddenly, they've got this burst of light energy and no competitors," Cardina said.

Multiflora rose, for example, can grow in dense thickets that choke out other plants. Its thorny branches offer no shelter for birds that normally nest in shrubs.

Other invasive plants can change soil chemistry or quickly suck up essential nutrients that native plants and microbes need to live.

That means the stakes are high for those who maintain public forests and parks.

"We have a staff person whose primary responsibility is dealing with invasive species," said John O'Meara, Franklin County Metro Parks director. With the ash borer, "it's only going to get worse."

David Lytle, state forester with the Ohio Department of Natural Resources, said that if invasive plants get a stranglehold, they can create simple ecosystems that could be devastated by a single disease or event.

"You keep pulling parts out of the (forest) machine and, eventually, it doesn't function as well," Lytle said. "It may break."

Cardina said he hopes their research will provide some good news.

"The question is, how long is it before we really do have these bigger impacts?" he said.