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Conserving Forests and Native Plants through Deer Management

The white-tailed deer is perhaps the most influential wildlife species in PA's forested ecosystems.  When their population is out of balance with habitat, they impact state forests and parks by browsing tree seedlings, shrubs, and wildflowers beyond their capacity to reproduce, impacting the ability to sustain a healthy, fully functioning forest.

To accomplish its mission of conserving Pennsylvania’s forests, DCNR manages deer on its lands and promotes sustainable deer management on all commonwealth forest lands.

Deer Management Assistance Program

The Deer Management Assistance Program (DMAP), established by the Pennsylvania Game Commission, allows DCNR to promote forest regeneration by targeting the most vulnerable and severely impacted tracts for additional antlerless deer harvests.

DCNR’s goals for DMAP are to:

  • Promote a diverse, healthy natural habitat that supports wildlife diversity and healthy deer populations
  • Provide additional hunting opportunities
  • Establish and maintain regeneration to support sustainable forestry practices with minimal need for deer fencing
  • Promote a healthy, sustainable forest and native, wild plant communities

To meet these goals, DCNR will follow these objectives:

  • Increase the number of native plants that are indicators of a balanced deer population
  • Increase the number of regeneration sample plots adequately stocked
  • Decrease the number of plants browsed by deer
  • reduce the need to fence for successful forest regeneration
  • Maintain good hunter participation

How Does DCNR Decide Where to Place DMAP Areas?

DCNR foresters and biologists determine where to place DMAP areas based on numerous criteria. One source is deer impact data.

DCNR collects data using a sampling protocol that assesses forest conditions in response to deer abundance.  Across 2.2 million acres of state forest land and 10,000 sample plots, DCNR staff are collecting data on these variables:

  • Percentage of plots with acceptable seedlings
  • Presence of native wild plants preferred by deer
  • Percentage of competing vegetation and site limitations
  • Percentage of species browsed

Foresters review this data to understand deer impacts in local forest districts. Other sources of information help determine DMAP decisions, such as:

  • Past regeneration successes or failures
  • Deer fencing needs
  • Current and future management activities
  • Sale of DMAP tags and hunter success rates

How Many Deer Should There be on State Forest?

There are many opinions about how many deer there should be on state forest land. While deer numbers can generate a lot of discussion, DCNR focuses its efforts on habitat conditions.

“Biological carrying capacity,” which refers to a forest’s ability to support deer while maintaining healthy habitat, can vary year to year.

Carrying capacity can change annually, seasonally, and across properties.

That is why on state forest lands, DCNR focuses its deer management activities on habitat conditions and collects forest health data to help determine DMAP enrollment.

Deer’s Impact on Habitat Conditions and Forest Growth

Establishing young forests enhances the mix of forest habitat and is good for other wildlife and overall forest health. Out-of-balance deer populations impact other wildlife and frustrate efforts to establish healthy, young forests.

Impacts to Other Wildlife

Over-browsing by deer alters the diversity and habitat for other forest mammals and birds. 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
  • Other small mammals

This in turn, reduces the predator populations that feed on them, including:

  • Owls
  • Hawks
  • Fishers
  • Other carnivores

In addition, over-browsing can eliminate the shrub layer and greatly reduce the diversity of forest-floor plant species. Many wildlife species utilize the shrub layer and feed on forest-floor plant species, such as:

  • Appalachian cottontail
  • Snow shoe hare
  • Ruffed grouse

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

Because more light is able to reach the forest floor and trigger new growth, plant and tree populations tend to increase after forest disturbances such as:

  • Timber harvests
  • Wind events
  • Insect outbreaks
  • Fires

This only occurs where deer impacts are low enough to allow this new growth to establish and flourish.

Excessive browsing of early forest regeneration can suppress certain tree species and promote the expansion of unpalatable or resilient species, further slowing the regeneration process.

By exhausting their major food source and obstructing forest regrowth, deer in high numbers can cause a forest’s ability to support future deer populations to decline.

Conclusion

The Bureau of Forestry recognizes the ecological importance and considerable influence of white-tailed deer on commonwealth forests, and is dedicated to maintaining a healthy forest plant community in balance with a healthy deer population.