Deer Impacts: Primary, Secondary (Interfering Plants), Tertiary (Faciltated Seed Predation)

Research Issue

Overabundant white-tailed deer (Odocoileus virginianus) herds have been shown to be a key determinant of understory plant species composition in  many parts of eastern North America over the last century.   The primary, direct effect of chronic overbrowsing is the reduction in growth and survival of browse-intolerant plant species which ultimately shifts species composition towards a few highly browse-tolerant or unpalatable species.  Such shifts in plant dominance patterns may secondarily result in altered plant-plant competitive dynamics in forests understories.  Finally, 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 Research

Over the past 50 years we have examined deer impacts on forest vegetation. Preliminary research showed the effects of deer overabundance on understory species composition. In the early 1970s, localized studies using exclosures clearly demonstrated that protection from browsing was necessary to regenerate forests in Pennsylvania’s Allegheny Plateau region.  By the 1980’s we moved beyond exclosure approaches to complete a stand-level enclosure study where vegetation development was monitored at 4 different known deer densities in four separate 160 acre sites.  Our current work builds upon these prior efforts by scaling up at to examine deer impacts at the landscape.  Across nearly 74,000 acres in the Kinzua Quality Deer Cooperative, deer population monitoring and extensive vegetation surveys are providing information on how both woody and herbaceous species respond to a systematic drop in deer levels.  Furthermore, we are extending our work to evaluate how deer browsing interacts with other factors (e.g., canopy gaps and fire) to influence vegetation structure.  

Results from this research and other regeneration research conducted by our unit in northwestern PA led to a partnership between the PA DCNR Bureau of Forestry and the US Forest Service Forest Inventory and Analysis (FIA) unit to include more detailed regeneration data collection on a subset of plots in Pennsylvania.  The results from these statewide studieshad a substantial influence on statewide forest and deer management policies.

Expected Outcomes

Results from our deer impact work continue to inform private, state, and federal forest resource management agencies, particularly in the specific management treatment sequence necessary to promote sustainable silviculture in the Allegheny region.  Our current work will provide insight into overcoming legacy effects of nearly a century of overbrowsing in the Allegheny region in order to sustain and promote biodiversity.  We will continue to improve our deer population/deer impact techniques including work on indicator plant species.  Finally, we will elucidate how deer impacts interact with other disturbances.

Research Results

Krueger, Lisa M., Peterson, Chris J., Royo, Alejandro, and Carson, Walter P., 2009. Evaluating relationshiops among tree growth rate, shade tolerance, and browse tolerance following disturbance in an eastern deciduous forest. Canadian Journal of Forest Research. 39: 2460 - 2469.

Reitz, S., A. Hille, and S. Stout.  2004.  Silviculture in cooperation with hunters:  The Kinzua Quality Deer Cooperative.   In:  Shepperd, W.D. and L.G. Eskew, compilers.  Silviculture in special places:  Proceedings of the National Silviculture Workshop.  September 8-11, 2003, Granby, Co.  Proceedings RMRS-P-34.  Ft. Collins, CO, USDA Forest Service, Rocky Mountain Station, pp. 110-126.

Horsley, S.B., S.L. Stout, and D.S. DeCalesta.  2003.  White-tailed deer impact on the vegetation dynamics of a northern hardwood forest.  Ecological Applications  13(1): 98-118.

Marquis, D.A.  1981.  Effect of deer browsing on timber production in Allegheny hardwood forests of Northwestern Pennsylvania.  Res. Pap. NE-475.  Broomall, PA:  USDA Forest Service, Northeastern Forest Experiment Station.  10pp.

Research Participants

Principal Investigators

• Alejandro A. Royo, USDA Forest Service- Northern Research Station Research Ecologist
• Susan Stout, USDA Forest Service- Northern Research Station Project Leader/Research Forester

Research Partners

• Todd Ristau, USDA Forest Service- Northern Research Station Research Ecologist
• Stephen B. Horsley, USDA Forest Service- Northern Research Station Scientist Emeritus
• David DeCalesta, USDA Forest Service, Retired.
• Kevin McAleese, Sand County Foundation.
• Chris Peterson, University of Georgia
• Lisa Krueger, University of Georgia
• Walter P. Carson, Univesity of Pittsburgh

For further information log on website :
http://www.nrs.fs.fed.us/sustaining_forests/conserve_enhance/timber/contrasting_silvicultural_systems/