You are here: NRS HomePartnerships / SILVAH


Deer Management in Pennsylvania

[photo:] Deer in lab pensDeer browsing has been the major factor affecting forests in Pennsylvania since the 1920s and continues to have a major impact today.  Prior to European settlement, deer abundance in Pennsylvania is estimated to have averaged about 12 deer per square mile.  Over the past 35 years, average deer abundance in PA has been nearly three times that high.  The primary impacts of deer over-browsing on forests include changes in species abundance, composition, and growth.  Over time, selective browsing on preferred species such as woody tree species and many forbs and shrubs, reduces species richness and shifts species composition towards less desirable browse-resilient species. Scientists at the Northern Research Station’s Forestry Science Lab in Irvine, PA, have been studying the impacts of deer on forest vegetation for more than 50 years. Much of this research has been informed by data gathered as part of a decade-long experiment comparing species abundance and diversity in forests where deer have been excluded (deer exclosures) with forest characteristics where deer are free to roam. 

Our research shows that the number of deer on the landscape can limit the ability of plants and other wildlife to survive there.  These results can persist for decades, even after deer abundance has changed.  More recently, our research focuses on the interaction of landscape patterns with deer density as a potential mitigator of deer impact on forest ecosystems. The partnership of public and private landowners, non-governmental organizations and public agencies that support the research and promote understanding of its results, have changed deer management policy. 


A strong partnership between the USDA Forest Service and the Bureau of Forestry within the Pennsylvania Department of Conservation has leveraged scientific expertise.

Studies are ongoing
Funding Institutions                            
Research Scientists Participating                       
Forest Service Researchers Participating
Annual Budget (approximate)
(both soft and appropriated dollars)



The long-term nature of these experiments has produced a continuing stream of data and publications.  NRS researchers have found that 

  • The primary direct effect of chronic deer overbrowsing is the reduction in growth and survival of browse intolerant plant species. 
  • Shifts in plant dominance may secondarily result in altered plant-plant competitive dynamics.
  • Through modification of plant composition and structure, deer overbrowsing may also exert indirect effects on the habitat and foraging patterns of other animal species.
  • Our current work will provide insight into overcoming legacy effects of nearly a century of overbrowsing in the Allegheny region.


Deer impact studies in Pennsylvania are being used as a basis for changing deer management policy in Pennsylvania. In turn, these changes have resulted in increased sustainability of forests. We have observed increases in the vigor and reproductive success (flowering and fruiting) of understory plants and some improvement in the diversity and abundance of tree species.

Lessons Learned

Scientists and managers, federal and state agencies, working together toward a common goal can achieve more than any of the entities can achieve working alone.

[photo:] Dr. Karl V. Miller, Warnell School of Forestry and Natural Resources, The University of Georgia “We laud the Northern Research Station for its role in the considerable effort of bringing together, creating ownership of, and incorporating the objectives of a diverse group of stakeholders toward development of an alternative deer management paradigm.”
--Dr. Karl V. Miller, Warnell School of Forestry and Natural Resources, The University of Georgia  

Partner Organizations

Last Modified: July 31, 2019