Culling sick trees may open forests to invasive plants

Holes in the forest canopy after ash trees were removed as part of the emerald ash borer eradication effort. The eradication may open the door for invasive species, according to a Kent State University researcher at the fifth annual Oak Openings Research Forum.

Attempts to rub out one bad actor from the forests of Northwest Ohio may have opened the door to a mob of other wildlife miscreants.

Constance Hausman, a researcher from Kent State University, is tracking the fate of the forest in Pearson Metropark after ash trees infested with the invasive emerald ash borer were cut down and hauled away in an attempt to stop the advance of the tree-killing pest.

Although the metallic green beetle continues its march through Ohio unfazed by attempts to cut off its progress, preliminary research suggests beetle eradication may be providing an invitation for a number of invasive plants, Ms. Hausman told the crowd of more than 100 gathered yesterday at the Main Branch of the Toledo Public Library for the fifth annual Oak Openings Research Forum.

Ms. Hausman began tracking changes in a variety of Pearson Metropark forest plots in 2005.

She is comparing plots where tree harvesting equipment rolled through the forest on caterpillar tracks and removed ash trees to plots where ash trees were left standing, regardless of infestation.

Forest plots where trees were harvested show increased soil compaction, and a greater degree of sunlight reaching the forest floor.

The result is an advance in undesirable invasive plant species into the forest. Those invaders include the white-blossomed garlic mustard, which can rapidly take over a forest plot and out-compete more desirable native plants, and the Canada thistle, a fast-growing European invader that can reach six feet in height, produce millions of seeds, and easily crowd out native plants.

Drastic changes in plant communities echo through the ecosystem, robbing insects and other animals of the food and cover they need, which can in turn mean less food for the animals that eat them.

Like many invasive species, garlic mustard and Canada thistle prefer disturbed areas - and the emerald ash borer eradication program is creating disturbance.

In these harvested plots, leaf canopy that sheltered the forest floor disappeared. Ms. Hausman's data showed plots that previously were seldom more than dappled with sunlight are now subject to direct sun for hours.

The heavy equipment squished the soil, most dramatically at the level where most plant roots reside. This compaction eliminated pockets of moisture and air that previously honeycombed even the heavy clay soils of the Pearson Metropark.

It will take decades for soils to recover from the compaction, she said, which also impairs the soil's ability to absorb rainfall, thereby increasing runoff and erosion.

Her future study will include forest plots where infested trees are removed without the use of heavy equipment, creating forest with less leaf cover but little soil compaction.

Elliot Tramer, a University of Toledo professor, is studying how an ash forest is changing as ash trees die in the Swan Creek area of the Oak Openings Preserve Metropark. Those trees are not being removed.

He's long been skeptical of efforts to stop the ash borer.

"I predicted it wouldn't work,'' Mr. Tramer said. "I'm certainly not surprised by any of Constance's preliminary data. They're creating an environment that's much more amenable to invasive plants."

Mr. Tramer says he doesn't expect to see the same attack of invasive plant species in the parts of the forest he's studying, despite the increased penetration of sunlight that's created when dead trees fall.

"In my area, because it's a flood plain, it's a very different type of regime. It tends to be nettles that come up in spring and stay up," he said. Those nettles may be able to block invasives from making inroads, particularly since the area will not face the additional complication of having soils compacted and torn up by heavy equipment.

If there's any good news in the ash borer invasion, it may be for medium sized woodpeckers, who appear to be enjoying a green beetle feast.

"In 10 out of 12 visits, red-bellied woodpecker were out there, hitting these ash borers very hard," Mr. Tramer said.

"Unfortunately," he said, "not hard enough to get rid of all the ash borers."

Contact Jenni Laidman at:

jenni@theblade.com

or 419-724-6507.