DCNR’s Role in Deer Management: Conserving Pennsylvania's Forests and Native Plants
The mission of DCNR Bureau of Forestry is to ensure the long-term health, viability and productivity of the Commonwealth’s forests and to conserve native wild plants.
To accomplish this mission, the bureau sustainably manages the 2.2 million-acre state forest system for many uses and values, including recreational activities such as wildlife watching and hunting. But the bureau’s role in forest conservation, however, extends beyond state-owned lands. The agency is charged with protecting all of Pennsylvania’s forests from wildfire and damaging agents, and conserving and managing the state’s native, wild plant communities. The bureau also promotes the knowledge of resources and forest stewardship.
White-tailed deer are perhaps the most influential wildlife species in the forest ecosystem. Through selective browsing of native plants, shrubs and trees, they influence the vegetation that grows and the health of the forest. Deer also influence other wildlife species and other forest values, and can impact their own habitat.
To accomplish its mission of conserving Pennsylvania’s forests, DCNR must manage deer on its own lands and promote sustainable deer management on all Commonwealth forest lands.
When deer are out of balance with their habitat they can cause negative impacts on forest vegetation. Overbrowsing by deer has eliminated the understory – the lower vegetation layer that includes young trees, shrubs and other plants – in large areas Pennsylvania. Although primarily thought of as shrub and small tree browser, deer also feed extensively on many herbaceous plants (such as wildflowers and other low-growing plants) and even fungi. Some forest plants that deer prefer include large white trillium, blue-bead lily, Canada mayflower, and numerous lilies and orchids. Because they never outgrow the reach of deer, forest floor wildflowers other plant species are continually vulnerable to deer impacts.
Forest Habitat and Wildlife
Overbrowsing can also alter habitat features important for forest mammals and birds, including deer. Direct effects occur when deer compete with other species for the same limited food source. For example, acorns and other tree nuts, known as mast, fluctuate greatly from year to year and are an important food resource for many forest mammals and some birds such as wild turkeys and blue jays. Competition for mast can cause a reduction in white-footed mice, deer mice, chipmunks, gray squirrels, and other small mammals, which can reduce predator populations that feed on them, including owls, hawks, fishers and other carnivores.
Indirect effects occur when deer alter habitat features. Overbrowsing has eliminated the shrub layer and greatly reduced the diversity of forest-floor plant species. Therefore, vertical diversity (plant, shrub, and canopy layers) and horizontal diversity (the patches of different plant species across the forest landscape) are greatly diminished. Many wildlife species, such as Appalachian cottontail, snow shoe hare, and ruffed grouse, utilize the shrub layer and feed on forest-floor species. Some birds, such as ovenbirds and eastern towhees, nest and feed in the ground layer. Reduced cover increases nest predation and decreases the ability of birds to raise their young successfully. Other species, such as eastern wood-pewee, indigo bunting, and black-and-white warbler, which use the middle layer of forest vegetation, have declined in heavily browsed forests.
Impacts to Forest Growth and Development
Forest disturbances, such as timber harvests, wind events, insect outbreaks and fires, have profound effects on deer populations. Populations tend to increase in response to these types of disturbance that allow more light to reach the forest floor and trigger new growth. This only occurs where deer impacts are low enough to allow this new growth to establish and flourish and competing vegetation such as ferns do not interfere.
Typically, the growth response from these disturbances is short-term, subsiding as the crowns of the canopy trees rapidly expand to fill their new growing space. Excessive browsing by deer during understory growth can suppress certain tree species. This selective browsing also promotes the expansion of unpalatable or resilient species, such as hay-scented fern, New York fern, and American beech or striped maple seedlings and saplings, that may slow or prevent the later regeneration by trees. By exhausting their major food source and fostering conditions that obstruct its regrowth, deer in high numbers can cause a forest’s ability to support deer populations decline.
Impacts to Forest Management
A deer population out of balance with its habitat impedes the practice of sustainable forestry in all forest types in Pennsylvania. On state forest lands, DCNR has specific goals for regenerating forests with many types of trees and creating a diversity of habitat across the landscape. Since our forests regenerated after the widespread clear-cutting that occurred in the early 1900s, many are approximately the same age—between 80 and 120 years old. Establishing young forests enhances the mix of forest habitat and is good for wildlife and overall forest health. Out-of-balance deer populations, however, can frustrate efforts to establish healthy young forests. Often, deer exclosure fences are required to encourage new growth.
ConclusionDeer populations, when out of balance with habitat conditions, can impact forest health and many forest uses and values. DCNR is responsible for conserving the Commonwealth’s forests and native plant communities. Science-based deer management that factors in habitat conditions is necessary to ensure healthy and sustainable forests.