Deer Herd Management
Baltimore County’s deer herd management program is necessitated by the deer-driven degradation of the forest ecosystems at a few of our largest forested parks. At the request of the Coalition for Responsible Deer Management, the Baltimore County Council authorized a deer cooperator (sharpshooter) program for Baltimore County parks in March 2011. Operations began with the 2011 to 2012 season, working with the Maryland Department of Natural Resources (MD DNR) Forest Service and the U.S. Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) Wildlife Services.
How Do Deer Affect Forest Health?
Deer are among the greatest agents of change in our forests today. Deer eat understory and ground vegetation, including the leaves of young trees and the acorns (seeds) of mature trees. In a balanced ecosystem, this behavior is benign. However, the dramatic overabundance of deer in Baltimore County forests has directly compromised the regenerative ability of the forests, reducing the ability of the forests to intercept rainfall, slow surface water flow, prevent soil erosion, filter ground water, and cycle nutrients. The lack of native plants in the understories of forests resulting from deer browse eliminates food and habitat for other wildlife, thereby reducing biodiversity. Deer’s preference for native plants also allows for the proliferation of invasive species, which shade the forest floor and prevent the germination of native tree seeds. In addition to browse pressure, many tree saplings die from buck rubbing. The overall significance of deer for changing forest ecosystems results in their designation as a “keystone” herbivore. As seen in the photo above, the excessively-browsed forest at Oregon Ridge Park contrasts with diverse forest growth inside a fenced private yard that excludes deer.
Why Are Deer Overabundant?
Deer population densities increased following European settlement in North America, when populations ranged from an estimated one to two deer per square mile (Alverson et al., 1988). Habitat modification, predator elimination, and protective legislation enabled deer populations to increase in the 1800s, but they soon dropped to near extinction with high market hunting pressure until the early 1900s. Since then, restrictive hunting legislation, development-driven forest fragmentation, and continued predator suppression have created unnaturally favorable conditions for the white-tailed deer (Rooney, 2001).
A study in March 2009 reported an average deer density in Baltimore County of 95 deer per square mile, with higher than average densities in parks and suburban areas (Gilgenast et al., 2009). Wildlife and forest managers recommend deer densities of 15 to 20 deer per square mile as a desirable herd density that will not degrade our forests.
White-Tailed Deer: Prolific Feeders, Prolific Breeders
Deer prefer oak leaves and acorns. A 150 pound deer consumes six to nine pounds of forage daily, which equates to 24 to 36 oak saplings per day. In addition, 57 percent of a deer’s summer diet is acorns. Does can bear 16 offspring in their lifetime.
What is Being Done to Protect Forests in Baltimore County from Deer?
Deer herd management in Baltimore County began with the City of Baltimore’s efforts to control deer at the reservoirs that supply drinking water for 1.8 million citizens in the Baltimore region. The City of Baltimore uses public bow hunting and deer cooperator approaches in the reservoir watersheds. Loch Raven reservoir, which has been managed for deer since 2008, is considered a priority area, as the 1,600 acres of forests there protect the quality of some 20 billion gallons of untreated drinking water.
Between 2008 and 2012, a total of 1,312 deer were culled (1,036 from managed bow hunting, 276 from USDA Cooperators) at Loch Raven Reservoir. High numbers of deer have also been culled from Liberty and Prettyboy Reservoirs, where public hunting has been allowed for decades (324 and 336 deer, respectively, during the 2011 to 2012 season).
Baltimore County entered a Cooperative Service Agreement with the USDA APHIS program for the 2011 to 2012 season at Oregon Ridge and Cromwell Valley Parks, following forest health assessments that showed significant adverse impacts of deer on forest regeneration. Under this agreement, deer harvest operations are conducted at night using infrared night-vision equipment with semi-silencers. Deer are processed and distributed to Baltimore County food banks.
At Oregon Ridge Park, with forest cover totaling 895 acres (1.4 square miles), the target sustainable deer herd population is approximately 21 deer at a density of 15/square mile. In January and February 2012, sharpshooters removed 60 deer from the park, representing less than half the number of deer counted during an informal helicopter survey in spring 2008. Cooperators removed 75 deer at Cromwell Valley Park and 50 at the adjacent Loch Raven Reservoir property in February 2012.
For the 2012 to 2013 season, Baltimore County received recommendations regarding culling an additional 50 deer each at Oregon Ridge and Cromwell Valley Parks, in response to ground-level Forward-Looking Infra-Red (FLIR) surveys that counted 75 deer and 67 deer, respectively, in one evening. Given that not all deer in an area are counted during the reconnaissance, it is expected that the deer reduction will be sufficient to significantly reduce deer pressure on the forest, perhaps allowing a break in harvesting for a year or more after 2013.
What are Other Risks Posed by an Overabundance of Deer?
In addition to hindering forest re-growth and reducing ecological diversity, overabundant deer populations act as hosts for Lyme and associated tick-borne diseases. They also destroy residential and commercial landscaping, damage agricultural crops, and cause dangerous and expensive deer-vehicle collisions. Indeed, Baltimore County’s map (PDF) of deer-vehicle collisions reveals a concentrated belt of accidents across the middle, suburban portion of the County, where deer are most abundant.
Managing deer at appropriate levels can ensure the presence of a sustainable deer population, while promoting the health of forests, protecting regional water quality, and lowering risks to people, crops, landscaping, and communities.
Alverson, W.S., Waller, D.M. and Solheim, S.L. 1988. Forests too deer: edge effects in northern Wisconsin. Conservation Biology (2), 348-358.
Gilgenast et al. 2009. A Study of the Deer Population of Baltimore County, Interim Report. Page 11.
Rooney, T.R. 2001. Deer impacts on forest ecosystems: a North American perspective. Forestry (74), 201-202.
Revised March 13, 2013