Efforts to rebuild strips of woods along streams here and nationwide are being hindered by dying tree saplings. MU professor’s studies shed light on the problem.
David Zegers in front of a fenced-off section of meadow while students Nathan Smith and Lindsey Clark check traps for mice.
David Zegers of Millersville University pinches an ear tag onto a meadow vole.
By AD CRABLE
Millersville
Updated Oct 03, 2008 13:34
The meadow vole, having spent the night confined in a live trap baited with rolled oats on a farm just west of Millersville, responds to its liberation by sinking its teeth into the hand of David Zegers.
The Millersville University biology professor has taken precautions, but he still feels the nip through the garden gloves.
Firmly pinching the vole — a type of mouse — by its rear legs to immobilize it, Zegers gently blows on the rodent's tiny head to blow the hair away from an ear. Then, he presents the vole with an ear piercing, attaching a numbered galvanized tag originally designed for the fins of fish. Zegers much prefers the method over the old way of tagging rodents — clipping off a toe.
The vole, none the worse for wear, is released back into the dew-dripping grass and sent on its way.
Zegers and what he finds out about voles and other meadow-loving mice may have a bearing on the quality of Lancaster County's many damaged streams and, by extension, the ailing Chesapeake Bay.
Once again allowing wooded buffers to grow up along streams is one of the simplest, least expensive and most effective ways of improving water quality. The riparian buffer strips, as they are called, catch soil and fertilizers running off adjacent farm fields.
They shade the stream, helping fish and aquatic life. They provide food and cover for a host of mammals, birds and bugs.
Pennsylvania leads the nation in setting aside land around waterways — nearly 200,000 acres — and improving it under the state-federal Conservation Reserve Enhancement Program.
But, there has been one notable road bump: Sometimes many of the tree saplings planted in the buffers die in the first several years. Mortality often ranges from 30 to 60 percent. Deer browsing is not the main culprit, as the saplings are placed in protective plastic tubes.
That's what happened to Daniel Yocom, a MU biology professor when he bought a farm outside of Millersville. In 2001, wanting to be a good steward, he took seven acres on both sides of an unnamed tributary to the West Branch of Little Conestoga Creek out of farm production and enrolled them in CREP.
But three years after planting the trees that he hoped would one day become a streamstide forest, 60 percent of them were dead. When he pulled the placement tubes up, some contained mice nests. Tubes had been dug under and eaten through. He found teeth marks on quite a few of the dead trees.
Yocum, who is doing his own research into which soil fungi might best support tree survivability, approached his colleague Zegers. Could such devastation have been from the ravages of meadow mice when they are known to eat tree bark during winter, he wondered.
So, as trees were replanted, Zegers, working with students and a small grant from MU's faculty grants program, set up parameters for a scientific study.
Around three plots, each 25 feet by 25 feet, the crew erected a screen fence with an anti-climbing armor of metal flashing and systematically began live-trapping and evicting the rodent population. Three other plots of the same size were unprotected. Twenty-three traps were placed in each grid.
Six times a year, four days a week, twice a day, Zegers and crew check the traps. This summer he is being aided by Lindsey Clark, a senior aspiring biology teacher from Airville, and Nathan Smith, a Cleveland State University senior provided by the National Science Foundation's Research Experience for Undergraduates.
The two get up at 6 a.m. — two hours earlier than the earliest class at MU — to sweat in the sun.
"It's a lot of repitition but it's fun because it's a surprise every time you open the (trap) door," says Clark.
So far, now in the fourth year of a six-year study, the team has caught several hundred meadow voles, Pennsylvania's most common vole — some get "trap happy" and return again and again for the oats.
Also trapped and released have been far lesser numbers of short-tailed shrews, Norway rats, white-footed mice and a few sparrows.
Are voles killing trees?
To his surprise, Zegers says in this field at least, it doesn't appear so. There is a 9 percent higher survivability rate in the plots with the protective fences, but, overall, most of the trees are living regardless of the high rodent population moving on runways under the heavy grass.
"It may end up they're (mice) not the big factor," Zegers says. "It may be a very localized thing." Or, mice may go after young trees only in particularly severe winters.
It may turn out another component of Zegers' study may be of most use.
The theory is that mice tend to avoid bright light and move around and eat in the dark, which is why they seek out fields of dense vegetation.
Would cutting grasses around the trees, letting in light, discourage mice movement?
Zegers' preliminary research is yes, they don't like to move in exposed areas. The emerging findings are buttressed by lab work in which voles chose feeding chambers with little or no light and avoided bright conditions.
The findings also may mean trees survive better in shorter plastic tubes as the standard 4-foot-tall tubes, though protecting against deer, make it dark at the bottom of the tree, thus inviting mice activity.
"So far at least, it seems to be telling us a story," says Zegers of the light and vegetation-height studies.
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Vole study