By Jeff Elder, Steve Young, and Kasha Helget
The white-tailed deer (Odocoileus virginianus) impact on local forests has grown, with the loss of many native trees and shrub seedlings to deer browse. ARMN provides detailed information about these adverse impacts in its “Learn About” feature entitled, Deer Population and Forest Health, as well as blog pieces posted 2020, and 2021 on the ARMN website.
ARMN has worked with Arlington County Park staff to construct and maintain deer “exclosures” in Gulf Branch and Glencarlyn parks in Arlington. These tall deer-proof fenced-off areas keep deer out of small areas of each park. The exclosures provide data on the effects of deer on our forests and help educate people who can compare protected and unprotected areas as they walk by.
The question is: do these exclosures work?
Gulf Branch Park
The deer exclosure was initially built as an Eagle Scout project in 2017. However, it had fallen on rough times (branches!) without subsequent repair. ARMN member Bill Browning talked to fellow member Jeff Elder about repairing the exclosure. So, Elder and his family did the work in November 2021. Browning organized a team of ARMN monitors to make weekly checks on the integrity of the exclosure. When branches fell on the exclosure, Elder would patch it back together. This June, Elder did an extensive evaluation inside and outside of the exclosure to see what differences could be sussed out of a deeper enumeration of vegetation on either side of the exclosure. He found much greater native plant biomass volume inside the exclosure than outside. Plants also tended to be healthier and maturing nicely within the exclosure compared to the less frequent, stunted, and sometimes chewed versions outside the barrier.
Area outside of Gulf Branch exclosure, heavily browsed by deer. Photo by Jeff Elder.
Elder also notes that the scale of the exotic invasives problem outside of the exclosure was and still is daunting. Elder concluded that setting aside areas in exclosures seems like a good protection measure analogous to marine sanctuaries in oceans. They help to preserve a diversity of native plant seeds despite any adverse conditions that may persist in suburban forests, especially those hard hit by overpopulated deer.
Glencarlyn Park
ARMN member Steve Young provided some background about how the deer exclosure came to be in the park. Before its present configuration that includes armament with rip-rap boulders, Long Branch stream meandered within its flood plain along a stretch from roughly Willow Pond along the access road to just before the Long Branch Nature Center (LBNC) building. In at least two spots, traces remain of steeper terrain where the outer edge of meanders began to cut from the flood plain into the banks. These features preserve remnants of old herbaceous plant communities that are largely absent elsewhere in the park. While the steeper grade reduced deer browsing pressure for a long time, as the deer population grew, browsing increased and plants began to disappear.
ARMN members and park staff agreed that it was worth setting up a smallish deer exclosure to protect one of these sites that happened to be located conveniently near the LBNC access road. So, volunteers erected the exclosure in July 2022. Even just two years later, the exclosure clearly is serving its purpose of protecting the native plant community. Like the Gulf Branch exclosure, the vegetation presence, abundance, and health are much greater inside than outside the fence.
Area inside of Glencarlyn exclosure, with plants that would be eaten by deer if not protected. Photo by Steve Young.
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