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Science Chronicles: Deer Overabundance and Ecosystem Degradation: A Call to Action

Allen Pursell, Troy Weldy and Mark White* 8/8/2013

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“I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer.” —Aldo Leopold, A Sand County Almanac, 1949
In August, 2012 The Bloomberg View published a staff editorial entitled Deer Infestation Calls for Radical Free-Market Solution. The Wall Street Journal then ran a story in November 2012 entitled America Gone Wild, noting the impact of overabundant deer. If business news organizations can talk freely about deer, TNC needs to speak openly as well. Aldo Leopold long ago warned us of the problems of a growing deer herd. Have we waited too long to heed his advice, or is there still time to reverse the damage done?

Photo: The forest understory is nearly absent except for Japanese stiltgrass. Note the deer appears to be especially thin. Valley Forge National Historical Park, PA. (Ron Rathfon)

No native vertebrate species in the eastern United States has a more direct effect on habitat integrity than the white-tailed deer. There are no hard numbers, but in many states deer populations continue to rise well beyond historical norms. In many areas of the country deer have changed the composition and structure of forests by preferentially feeding on select plant species.
In northern Minnesota, TNC staff demonstrated that decades of overbrowsing led to recruitment failure for many tree species, a shift in subcanopy and canopy dominance towards non-preferred white spruce, and significantly lower forest productivity (White 2012). In New York, TNC scientists report that one-third of New York’s forests are currently compromised as a result of excessive herbivory (see New York Forest Regeneration Study).
Findings similar to these have been documented across the country. U.S. Forest Service researchers have noted that even if areas with high deer densities were managed to reduce the impact of deer, there may be long-lasting legacy effects (Royo 2010). Webster (2005) found severe and lasting impacts at Smoky Mountain National Park to be so complete that some plants such as trilliums were unlikely to recolonize local areas on their own. Deer are also well-documented vectors for the dispersal of non-native exotic plants (Knight et al. 2009, Baiser et al. 2008, Williams and Ward 2006).
Indirect effects on wildlife have been reported as well, such as widespread declines of North American songbird populations (Chollet 2012). One study found forest songbirds that preferred nesting in the shrub and intermediate canopy layer declined in abundance and species richness as deer density increased (deCalesta 1994).
White-tailed deer likely impact every landscape east of the Mississippi River. The damage has been insidious — both slow moving and cumulative. Unfortunately, the harm is often overlooked, or worse, accepted as somehow “natural.”
In our opinion, no other threat to forested habitats is greater at this point in time — not lack of fire, not habitat conversion, not climate change. Only invasive exotic insects and disease have been comparable in magnitude. We can argue about which threat is more significant than another, but no one who walks the eastern forests today can deny the impact of deer to forest condition.
It is clearly true that fire suppression has had a widespread impact on successional trajectory and tree species composition. A natural fire return interval would be a great benefit to many eastern forests. Yet even where fire is present, excessive deer herbivory has been shown to depress tree species diversity or at least minimize the benefits of fire. In the words of a recent study on the interactions of fire, canopy gaps, and deer browsing: “… restoring disturbances without controlling browsing may be counterproductive.” (Nuttle, 2013)
While we acknowledge that climate change is a long-term stressor that will lead to significant changes in eastern forest ecosystems, high deer populations have had a much greater negative impact currently and over the last several decades. At present there is little evidence of direct climate change impacts on eastern forests (Beckage et al. 2008, Woodall et al. 2009, Zhu et al. 2012, Rustad et al. 2012). With climate envelope and other modeling systems, we have a general understanding about likely range shifts and compositional changes in eastern forests over the next 50-100 years. However, due to the many interacting factors such as atmospheric deposition (nitrogen, ozone), insect pests and pathogens, invasive plants, CO2 enrichment, longer growing seasons, and white-tailed deer populations, there is a high degree of uncertainty about the future condition and function of eastern forests in a changing climate (Frelich and Reich 2009, Rustad et al. 2013).
No such uncertainty exists regarding the negative impacts of high deer populations on eastern forests; the body of evidence is unequivocal. In this article, we present only a small fraction of the literature on deer impacts. Reducing the impact of deer herbivory is currently a key forest restoration strategy (White 2012, Nuttle et al. 2013) and likely will become more important in order to help maintain resilient, functioning forests in a warming climate (Galatowitsch et al.2009).
Engaging society to address the problem will be difficult, probably similar to our experience with wild pig eradication in California and Hawaii, but on a wider scale. Views on deer management are deeply entrenched, both among those who hunt and those who don’t. People have strong opinions when it comes to deer. If The Nature Conservancy were to take an unambiguous position that deer densities must be lowered, we would certainly make enemies and possibly lose donors, but new alliances could emerge.
Natural Allies?
TNC can look to a number of non-traditional partners in an effort to influence policies that reduce deer numbers. Among these partners are hunters, auto insurance companies and the driving public, the public health sector, the timber industry, and agriculture. We provide a brief rationale for each of these below.
Hunters. Hunters spend billions of dollars each year in pursuit of white-tailed deer. The success of the Quality Deer Management Association (QDMA) in attracting members is evidence that many hunters, especially younger hunters, increasingly understand that deer must be managed in balance with their habitat. QDMA’s philosophy revolves around “Healthy Habitat, Healthy Herd.” Such hunters could be very helpful.
Insurance Companies and the Driving Public: State Farm Insurance estimated that in the year ending June 30, 2012, there were 1.23 million deer-vehicle collisions in the U.S. The chance of a driver striking a deer during those 12 months was 1 in 171 nationwide, but as high as 1 in 40 in West Virginia. The cost is enormous with an average expense of $3,305 per collision, totaling over $4 billion nationwide (State Farm Mutual Automobile Insurance Co. 2012). In West Virginia there were an estimated 30,203 deer-vehicle collisions in 12 months — roughly $83 for every licensed driver in the state. Ask drivers whether they are concerned about deer on roadways, and most will say, “Yes!”  At a public hearing, someone stood up and said, “I’m here because Indiana was once a great place to ride a motorcycle. Not anymore. There’re too many deer.” Insurance companies and public safety interests could make a big difference supporting deer reduction strategies.
State Farm deer map
Map from State Farm Insurance Co.
Public Health Sector: There is strong evidence that the rise and spread of tick-borne illness is associated with large numbers of deer as deer can be significant reservoirs of tick-vectored diseases (Allan 2010). The threat of contracting a tick-borne disease is prominent in the minds of many. The public health sector — both government and private — could be effective partners in managing for lower deer densities, with testimonials by individuals whose lives have been affected by tick-borne illnesses.
Timber Industry: Foresters have long held that deer browsing limits silvicultural options. Take the Central Hardwoods Region and Appalachians where oak forests are not successfully regenerating. Deer browsing has led to an understory dominated by ferns — at the expense of valuable oak seedlings — across large areas of the Allegheny Plateau.
Agriculture: Given their economic motivation, farmers could be persuasive allies in deer management policy. In 1990, crop damage associated with deer topped $318 million nationwide (Fagerstone and Clary 1997). Perceptions of farmers toward deer and other wildlife reveal that many of them (40%) would oppose the creation of a wildlife sanctuary near their property because wildlife damage is so severe (Conover 1998). Most farmers (53%) in this same study attributed their problems to deer. Livestock producers are not immune either. Wild deer in at least two states are known to harbor bovine tuberculosis, a disease of great concern to cattle producers. 
A Call to Action
Change is possible but it won’t be easy or quick.
Deer management cannot be regulated at the federal level. As early as 1896 the Supreme Court ruled that states have "ownership" of their wildlife. As a result, each state has its own intricate rules. State regulations need not be standardized, but efforts at reform must be made state-by-state. This process will be slow as rules are generally promulgated by processes that ensure adequate evaluation by respective wildlife authorities and to allow for public review.
Nevertheless, some states are beginning to do the difficult work of changing policies to stabilize or reduce the number of deer. For example, Indiana recently enacted the first modern firearms season targeting female deer in the state’s history.
It will be difficult to overcome traditional hunter concepts of proper deer management as it is counter-intuitive to most hunters that fewer game animals are desirable. Decades of effort, patience, and expense were invested to enhance populations to the point where hunting success is now commonplace. To suggest that populations be reduced and therefore increase the effort needed to harvest a deer understandably generates resistance. Success will take a carefully crafted and sustained public relations effort.
Like almost all conservation problems, deer management is a societal issue. If the deer population is to be reduced, it must be reduced slowly. Rules that lower the population drastically will almost certainly spur a backlash from hunters who can appeal to their respective legislatures to overturn regulations they regard as harsh. In an effort to lower the population of deer in Wisconsin the DNR liberalized hunting dramatically. The result was a hunter revolt. Gov. Scott Walker campaigned on a pledge to fix deer management. Once elected, he made good on that promise by appointing a deer trustee to evaluate his state’s DNR. The trustee’s final report noted that by failing to adequately communicate with hunters and involve them in determining solutions the DNR had lost credibility (Kroll 2012). A similar push back may be occurring in Pennsylvania.
We propose the following:
  • Establish a working group, including representatives from TNC field offices, Central Science, and GR, to develop two products: 1) an organization-wide position statement on the deer issue; and 2) a toolkit for addressing deer overabundance state-by-state;
  • Report these recommendations to staff and trustees;
  • Reach out to traditional and non-traditional partners at the national level, including the Quality Deer Management Association; and
  • Encourage operating units to use the toolkit to address specific state-level policies that have led to unnaturally abundant deer.

TNC’s three primary conservation strategies are to 1) Protect and restore natural systems, 2) Use nature sustainably, and 3) Broaden support for conservation. A carefully crafted solution addressing the challenge of elevated deer populations will do all three.
In some sense one of the greatest losses of all is that deer are no longer viewed as the majestic and even mystical animals of the forest that they were only a few decades ago. To quote Bloomberg: “… it’s hard to think of a more insidious threat to forests, farms and wildlife, not to mention human health and safety, than deer.”   
How different that is from the time of John Muir, who wrote, “Standing, lying down, walking, feeding, running even for its life, it [deer] is always invincibly graceful, and adds beauty and animation to every landscape — a charming animal and a great credit to nature.”
Allen Pursell, Southern Indiana program director, The Nature Conservancy | Troy Weldy, director of ecological management, The Nature Conservancy in New York | Mark White, forest ecologist, The Nature Conservancy in Minnesota and the Dakotas
Allan B.F., L.S. Goessling, G.A. Storch, and R.E. Thach. 2010. Blood meal analysis to identify reservoir hosts for Amblyomma americanum ticks. Emerging Infectious Disease 16(3):433-440.
Baiser, B.J., L. Lockwood, D. La Puma, and M.F.J. Aronson. 2008. A perfect storm: two ecosystem engineers interact to degrade deciduous forests of New Jersey. Biological Invasions 10: 785-795.(Beckage, Osborne et al. 2008)
Beckage, B., B. Osborne, et al. 2008. A rapid upward shift of a forest ecotone during 40 years of warming in the Green Mountains of Vermont. Proc Natl Acad Sci USA 105: 4197-4202.
Beckage, B., B. Osborne, D.G. Gavin, C. Pucko, T. Siccama and T. Perkins 2008). "A rapid upward shift of a forest ecotone during 40 years of warming in the Green Mountains of Vermont." Proc Natl Acad Sci USA 105(11): 4197-4202.
Bloomberg View. (2012, August 8). Deer infestation calls for Radical Free-Market Solution. Bloomberg.com. Retrieved January 18, 2013 from http://www.bloomberg.com/.
Chollet, S. and J. Martin. 2012. Declining woodland birds in North America: should we blame Bambi? Diversity and Distributions doi: 10.1111/ddi.12003.
Conover, M.R. 1998. Perceptions of American agricultural producers about wildlife on their farms and ranches. Wildlife Society Bulletin 26(3):597-604.
deCalesta, D.S. 1994. Effect of white-tailed deer on songbirds within managed forests in Pennsylvania. Journal of Wildlife Management 58(4): 711-718.
Fagerstone, K.A. and W. H. Clay. 1997. Overview of USDA Animal Damage Control Efforts to Manage Overabundant Deer. Wildlife Society Bulletin 25(2): 413-417.
Frelich, L.E. and P.B. Reich. 2010. Will environmental changes reinforce the impact of global warming on the prairie–forest border of central North America? Frontiers in Ecology and the Environment 8: 371-378.
Galatowitsch, S., L. Frelich. 2009. Regional climate change adaptation strategies for biodiversity conservation in a midcontinental region of North America. Biological Conservation 142: 2012-2022.
Knight, T.M., J.L. Dunn, L.A. Smith, J. Davis, and S. Kalisz. 2009. Deer facilitate invasive plant success in Pennsylvania forest understory. Natural Areas Journal 29(2): 110-116.
Kroll, J.C., D.C. Guynn, Jr, and G.L. Alt. 2012. Final Report and Recommendations by Wisconsin White-tailed Deer Trustee and Review Committee. 2012. Madison, Wisconsin. 136 pp.
Nuttle, T., A.A. Royo, M.B. Adams, and W.P. Carson. 2013. Historic disturbance regimes promote tree diversity only under low browsing regimes in eastern deciduous forest. Ecological Monographs 83(1): 3-17.
Royo, A.A., S.L. Stout, D.S. deCalesta, T.G. Pierson. 2010. Restoring forest herb communities through landscape-level deer herd reductions: Is recovery limited by legacy effects? Biological Conservation 143: 2425-2434.
Rustad, L., J. Campbell, J. Dukes, T. Huntington, K. Fallon Lambert, J. Mohan, N. Rodenhouse. 2012. Changing Climate, Changing Forests: The Impacts of Climate Change on Forests of the Northeastern United States and Eastern Canada. USDA Forest Service, Northern Research Station General Technical Report NRS-99: 56pp.
State Farm Mutual Automobile Insurance Co. (2012, October 23). It’s West Virginia Again. Mountain State Leads State Farm’s List of States Where Deer-Vehicle Confrontations Are Most Likely. Statefarm.com. Retrieved January 18, 2013 from http://www.statefarm.com/.
Wall Street Journal. (2012, November 2). America Gone Wild. online.wsj.online.com. Retrieved January 18, 2013 from http://online.wsj.com/. 
Webster, C.R., M.A. Jenkins, J.H. Rock. 2005. Long-term response of spring flora to chronic herbivory and deer exclusion in Great Smoky Mountains National Park, USA. Biological Conservation 125: 297–307.
White, M.A. 2012. Long-term effects of deer browsing: Composition, structure, and productivity in a northeastern Minnesota old-growth forest. Forest Ecology and Management 269:222-228.
Williams, S.C. and J.S. Ward. 2006. Exotic seed dispersal by white-tailed deer in southern Connecticut. Natural Areas Journal 26(4): 383-390.
Woodall, C.W., C.M. Oswalt, J.A. Westfall, C.H. Perry, and A.O. Finley.  2009. An indicator of tree migration in the eastern United States. Forest Ecology and Management 257: 1434-1444.
Zhu, K., C.W. Woodall and J.S. Clark. 2012. Failure to migrate: lack of tree range expansion in response to climate change. Global Change Biology 18: 1042-1052.