Deer may be a bigger threat to Eastern forests than climate change.
By Allen Pursell, Southern Indiana Program Director, The Nature Conservancy in Indiana; Troy Weldy, Director of Ecological Management, The Nature Conservancy in New York; Mark White, Forest Ecologist, The Nature Conservancy in Minnesota and the Dakotas
“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, The Nature Conservancy (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?
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.
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