Deer Excluded in Pursuit of Research

| February 27, 2009

Two Odocoileus virginianus cruising the northern base of Monument Hill for tasty shoots poking through the forest floor stop suddenly.

“What the heck?” one mutters to the other. “Hal, do you see that?”

Before the white-tailed deer is a black mesh fence, nearly invisible in the gloaming light but for the yellow and white plastic flags tied along its length. Inside the roughly 49- by 33-foot enclosure, is nothing different than what is outside the fence — yet.

Assistant professor of biology Janet Steven suspects that, over time, there will be an observable change in the flora that carpets the ground inside the fence. Furthermore, she and her colleagues in the biology department theorize that the real deer on whom the aforementioned fictional Hal and his talking companion are modeled, will have something to do with it.

The white-tailed deer population on Sweet Briar’s campus is big and getting bigger, leading to concerns that overgrazing is harming the diversity of native plants that grow here. There is historical evidence to suggest a problem, thanks to plant lists compiled by Ernest P. “Buck” Edwards, who retired from Sweet Briar as Duberg Professor of Ecology in 1990, and his late wife, Mabel Thacher Edwards.

“While we have no record of the abundance of individual species in the past, Buck and Mabel Edwards’ plant list from the eighties has species I’ve never seen blooming on campus in the four years I’ve been here,” Steven said last fall, when plans for building a “deer exclosure” for research purposes were first discussed.

On a recent warm day in mid-February, a crew of about 15 biology and environmental sciences majors erected the 7-foot-high fence in an area that Steven, biology professor Linda Fink and SBC naturalist-in-residence Michael Hayslett had previously staked out for the project. Hayslett and Fink led the effort, which also got a boost from Bill Perry of the Virginia Department of Forestry and volunteer Nat Reasor, a certified Virginia Master Naturalist with the local VMN program.

The nifty fencing system, which was purchased online, went up in an afternoon. The vertical posts slide into hollow sleeves that can be pounded into the ground — no laborious post-hole digging. The high-strength polypropylene mesh grid is secured to the posts with zip ties. Following Hayslett’s direction, the students cleared a corridor in the brush about 2 feet wide and 8 feet high for the fence line.

Keeping vines and branches away from the fence distorts the deer’s depth perception, discouraging them from attempting to leap the barrier, he explained. White-tailed deer can clear a 6-foot obstacle, he said, if they can judge its height. The plastic flags were installed to prevent them from running into the mesh, which is designed to disappear against the background foliage.

Steven said Monument Hill has both high deer densities and good plant habitat, and it’s easily accessible for classes. This spring and summer, she and her Plant Kingdom students will take data on the abundance and size of understory plants and shrubs growing inside the exclosure. The same observations will be recorded in a control plot outside of the fence.

“We will compare the two to estimate the impact of deer on plant growth,” Steven said later in an e-mail describing how the data will be used. “Over the years, students will be able to use both the data they collect and data from previous years to determine whether plant populations are declining because of overgrazing by deer.”

She said future classes might look in more detail at the effects of grazing on a particular species, compare biodiversity inside and outside of the exclosures, or examine the impact of deer on invasive plant species.

“In addition, as patterns become more obvious, we may incorporate a lab into Introduction to Organisms and or Laboratory in Plants and Human Affairs that uses the exclosure,” Steven said. “If this exclosure generates good data, we will also look into putting up more exclosures across campus.”

Fink, who predicted that the exclosure will yield differences in plant growth pretty quickly, noted that the project will serve a valuable purpose regardless of the outcome. “It’s a learning experience,” she said. “The process of doing it is as important as the data.”

Jennifer McManamay

Category: Academics, Environmental Science, Environmental Studies