by Leslie Cameron and Bill Browning
In mid-November, ARMN members Bill Browning, Jeff Elder, Steve Young, and Leslie Cameron met with Arlington Parks and Recreation Conservation and Interpretation Manager Rachael Tolman to evaluate a deer “exclosure” in Gulf Branch Park.
The deer exclosure was built in 2017 as part of an Eagle Scout project for a local Boy Scout troop to protect the vegetation inside from deer browse. As the white-tailed deer (Odocoileus virginianus) population in Arlington has grown, their impact on Arlington’s forests has grown too. Deer exclosures are one strategy for protecting habitat from deer browse and can also play a role in collecting data on the impact of deer in our forests. They can also potentially play a big role in educating people, who can compare protected and unprotected areas as they walk by. In the 4 years since it was constructed, the deer exclosure in Gulf Branch has fallen into disrepair.
The group discussed repairing or rebuilding the exclosure (exclosures need to be 8-10 feet high to effectively exclude deer) and reducing the size to make it easier to maintain. To collect data on the impact of deer, a fenced exclosure (the “variable”) is paired with a same-size nearby unfenced reference plot (the “control”). The diversity of species and quantity of vegetation in both plots is documented over time. Signage can inform the public about the project, as well as discourage residents from disturbing it.
Impact of deer on a healthy forest
Deer are Virginia’s largest herbivore. An adult eats 5-7 pounds of vegetation a day, or a ton each year. If there are more deer than the land can support, deer browse begins to degrade the understory in a forest. The forest understory—forest floor, herbaceous plants, shrubs, seedlings, and young trees—supports native ground-nesting birds, insects, reptiles, and amphibians. Deer browse limits the food and cover for these species, and they decline. The understory also includes the young trees that form the forests of the future. A forest without its understory cannot regenerate, which means that there will be no mature trees in the future. Because deer prefer native plants, deer browse disturbs the diversity of plants, and allows invasive plants to multiply in their place.
Male deer also rub antlers on trees, which can damage them. For more background on the effects of deer on our forests, see the May 2020 ARMN blog article, “White-tailed deer and Forest Health in Northern Virginia.”
Deer population over time
By the 1930s, deer had almost disappeared from Virginia and had declined in many eastern states. States implemented regulations to protect deer and their habitat, and the population began to rebound. Effective predators of deer (like the gray wolf and eastern cougar) were extirpated from Virginia, and development and fragmentation have increased edge habitat, which deer prefer. These changes have contributed to a rapid increase in the population of deer.
Assessing Arlington’s deer population and next steps
In response to concerns about the impact of deer in Arlington’s forests and other natural areas, Arlington County hired an independent contractor to conduct a drone survey of the population in spring 2021. Some Federal property owners (National Park Service, Pentagon, Arlington National Cemetery, Reagan National Airport) did not grant permission for the aerial drones so these areas were excluded. Further, the contractor was unable to obtain a permit to fly the drones at night when the heat signatures are easier to detect. The survey counted a minimum of 290 deer in Arlington that were concentrated in wooded and natural areas. Four of the survey sections had deer counts at levels which most experts agree is too high for regeneration of native plants. All of Arlington’s seven Natural Resources Conservation Areas had too many deer. The contractor recommended aggressive deer management, particularly in those areas.
Arlington is in the process of hiring a second consultant to determine if a deer management strategy is needed and if so, to develop an implementation plan. Please see the County’s website for its current plan.
One management strategy some jurisdictions have considered is immunocontraceptive vaccines such as porcine zona pellucida (PZP) or GonaCon. In practice, this strategy has challenges with open herds. Annual injections may be needed to produce infertility. These vaccines are injected by hand into captured deer or hypodermic darts are fired remotely. Deer are susceptible to capture myopathy muscle damage that results from the extreme stress of being repeatedly captured. Darts delivered remotely can miss the target or fall out before delivering the dose. Despite many attempts nationwide, there are few reported instances where these medical intervention strategies have proven even marginally effective. Moreover, the Virginia Department of Wildlife Resources does not approve of these techniques for managing the size of deer herds.
Another strategy is managed hunting, which can take several forms, depending on location. This method usually involves professional sharpshooters or volunteers with rifles or archery tackle. Managed hunts can be conducted safely in restricted or urban areas, and done properly, result in very low rates of nonlethal wounding for deer. As noted in the 2020 ARMN blog piece cited above, neighboring jurisdictions have taken steps to manage their deer populations. Fairfax County has had a deer management program in place since 1998. Montgomery County established a deer management program in 1996. Both counties use all three hunting methods. The National Park Service established a deer management plant in 2012; the NPS primarily uses professional sharpshooters who hunt at night in collaboration with a variety of police authorities. All three jurisdictions have had no safety incidents since their programs’ inceptions.
Where they are highly concentrated, deer are damaging forests and degrading habitat in Arlington, at the expense of the other species that occupy the ecosystem, including mammals, birds, reptiles, and insects. Without natural large predators (wolves or mountain lions,), the deer population is out of balance. It is important to take steps to restore this balance to protect the future of Arlington forests and all their inhabitants.
Actions members of the public can take
Learning about the impact of deer on forests and other natural areas is critical. Anyone can assist in education efforts:
- Share this blog piece with friends and neighbors in community newsletters and on “Next Door” or other community social media.
- Is your neighborhood community group interested in a deer education presentation? If so, send that information to ARMN via “Contact Us” on armn.org.
- Ask about nature walks to bring attention to the impact of deer in natural areas via ARMN’s “Contact Us” feature.
- Participate in Arlington programs that are approved to rebuild and maintain deer exclosures and gather data on the impact of deer on natural areas.
- Avoid feeding deer or encouraging them to approach. You may also protect your landscape with a deer exclosure and other strategies. For more details, see: Virginia Cooperative Extension publication, “Deer: A Garden Pest.”
For more information
The following resources have more information about the impact of deer in natural areas and about Arlington’s process for assessing the problem and determining next steps.
Arlington County Deer Survey and Next Steps: