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‘Exclosive’ Coverage

Fencing “exclosures” in Gold Mine Tract part of multigroup study on deer population and plant survival.

If you were a local tree, what kind of a local tree would you be?

The question is largely irrelevant — many saplings in the C&O Canal National Historical Park face long odds against reaching adulthood.

It’s less obvious in winter months, but a visitor to the park in the summer or late spring can get a different perspective just by crouching down. In many areas of the park near Great Falls, plants and trees are devoid of leaves below eye level.

“What we call it is a ‘deer browse line,’” said Marie Sauter, a biologist and natural resource specialist a C&O Canal National Historical Park. “You can see the leaves of the trees come down to a certain point. [Below] it can often be as clean as a whistle.”

The Gold Mine Tract of the park, near Great Falls, is home to 39.9 deer per square kilometer. “That’s twice of what is believed to be ecologically sustainable levels,” said Stephanie Flack of the Nature Conservancy.

Much like the county’s swollen deer population devours home gardens in residential areas, too many deer can wreak havoc on a park’s ecosystem as well.

“Deer can really hammer vegetation,” Flack said. “We have a whole generation of missing trees.”

HIKERS OR JOGGERS who frequent the trails of the Gold Mine Tract may have noticed small fenced-in areas near the pathways. They were built last month as part of a study on the interaction between deer and plant species, which scientists and naturalists are conducting on federal parkland on both sides of the Potomac River.

“From The Nature Conservancy’s perspective, this is a really important study, because it affects the Conservation Plan,” Flack said.

She’s referring to the 2001 Potomac Gorge Site Conservation Plan, a joint study between

the National Park Service and The Nature Conservancy.

The study names deer as one of the great threats to the natural resources of the Gorge, which is home to more than 200 rare species.

Some of the rare plant species are under increasing threat from several directions. Some non-native, or “invasive” plant species such as garlic mustard or stiltgrass, grow like wildfire in some areas of the Potomac Gorge.

Officials conducting the study hope to determine whether deer overpopulation worsens the imbalance of native and invasive plants.

THERE ARE SEVERAL ways that deer overpopulation may result in invasive plant species’ proliferation. First, the deer might just think that native species are tastier.

“It is believed that deer may preferentially eat native species,” Flack said.

For starters, deer may eat the native plant species, causing invasive ones can spring up in their absence.

“When we don’t have our healthy vegetation, our natural vegetation, creating a community out there … it paves the way for invasive plants,” Sauter said.

Like people, deer can also unknowingly spread invasives if seeds stick to their fur or their hooves.

AND WHAT IF the deer don’t feast on native plants? That’s part of what scientists hope to find out, hence the fencing “exclosures” throughout the Gold Mine Tract. Each exclosure surrounds a selected plant species or group of plant species.

Scientists conducting the study will monitor the plant diversity within each exclosure over time, as the fencing (hopefully) prevents deer from foraging on the flora within.

The exclosures have a flier attached to the fencing, explaining the project (see “Exclosure Signs” information box). Overall, there are 60 study plots of 16 square meters apiece in the Gold Mine Tract, 20 of which are fenced in.

Rod Sauter, Marie Sauter’s husband and a ranger at C&O Canal National Historical Park, hopes park visitors will remain on the marked trails of the Gold Mine Tract.

“People of course are going to be curious and walk up to them,” Rod Sauter said about the exclosures. “[We ask] for folks to try to observe them from a distance.”

Fliers on the exclosures encourage park visitors with questions about the project to call the National Park Service.

“We certainly are encouraging people to ask, be inquisitive and be informed,” Marie Sauter said.

BIOLOGISTS AND other scientists involved with the study expect it to be long-term, at least for 10 years, according to Marie Sauter.

Thus, there are no near-term plans for deer population control on the federal parkland. Montgomery County oversees managed deer hunts on local parkland each year, including an annual one at Blockhouse Point Conservation Park over the past four years.

Such deer control remedies are not going to take place in the federal land of the Potomac Gorge in the near future.

“We can’t do it without the science to back it up,” Marie Sauter said. “We’re collecting data and collecting information so we can get to that point.”