Conservation Priority: Controlling Populations of White-Tailed Deer
White-tailed deer, (Odocoileus virginianus), are beautiful animals, part of the natural fabric of North America, adaptive and graceful. Deer are prey species, requiring predators to keep their populations in check. Without predators removing at least 40% of a deer herd per year, deer populations quickly grow and they eat more of the plants, nuts and seeds than an ecosystem can sustain. “Ecological carrying capacity” is the term for the point at which the number of organisms in a species become so abundant that they alter the ecosystems they live in. White-tailed deer have exceeded theirs.
Contrary to commonly held beliefs, suburban landscapes do not take away deer habitat – they create it. Deer are adaptive animals. Suburban development creates preferred edge habitat for deer, and human landscapes provide high concentrations of edible plants close to the ground where the deer can get to them. You can grow more deer in suburbia than you can in a purely forested landscape. The same is true in rural areas where forests are broken up by agricultural fields, pastures, house lots and powerline easements.
Deer are a prey species that requires predation to control their populations. Without predation they can double their numbers in as little as one year. With abundant food in rural and suburban landscapes, and almost no hunting pressure in suburban areas and declining hunting pressure in rural areas, deer numbers have skyrocketed state-wide. In many areas of the state, deer population numbers are at more than three to eight times the densities that native plant communities can sustain.
Biologists began to notice impacts from excessive deer browse in some parts of the country as early as the 1940s. Research began in earnest in the 1970s. Staff from the Virginia Department of Game and Inland Fisheries estimates that the Virginia deer herd numbers about 1 million animals. White-tailed deer are large herbivores, needing about 5 pounds of forage a day, with each animal eating about a ton of leaves, shoots, twigs, seeds and nuts per year. That equates to over a million tons of Virginia’s biota being converted to deer biomass per year. There are more deer and less of everything else.
This is happening across the state, a widespread filter of browsing animals steadily impacting our native plants. If left unchecked, deer browse will remove hundreds of plants and thousands of insects and dozens of small animals that depend on them. The losers include orchids, trilliums, oaks, milkweeds, hickories, blueberries and many other plants that provide food and shelter to numerous insects and birds.
The winners include a shortlist of native plants such has hay-scented fern and a long list of invasive plant species that support few other species. The difference is one between a native landscape with numerous wildflowers through spring and summer, abuzz with activity, compared to a simplified green landscape, devoid of colorful flowers and the sound of forest dwelling birds – an impoverished environment.
Henry Wilbur, retired Professor of Botany at the University of Virginia, has been working for the past nine years to show the correlation of deer browse to native plant decline in controlled experiments at the Mountain Lake Biological Research Station in Giles County, Virginia. Professor Wilbur and his colleagues demonstrated that over an eight year period, deer browse began to reduce the total number of plant species and dramatically reduced the size, abundance and ability to reproduce for most of the forest herbaceous plants. This research shows that plant energy reserves are decimated as they try to grow with repeated browsing. Further research will be done to determine the rate at which these plants go extinct in a forest stand over time.
Researchers from Cornell University found that deer browsing not only removes many native plants from the forest ecosystems, but alters the seed bank so that those species cannot return and forest succession is impacted for hundreds of years.
The result is that our remaining forest ecosystems are decimated. Deer eat everything native with few exceptions. They eat almost all of the non-woody plants in the forest as well as all shrubs and trees within their reach as well as the majority of the acorns and hickory nuts. They have now removed most vegetation from many of our forests below 5 feet.
The impacts include the loss of many of our woodland wildflowers, a change in forest stand composition to a few species such as tulip tree, American beech and red maple that have smaller seeds and appear to be less palatable to deer, and the disappearance of up to 75% of our forest bird species in many areas due to loss of the understory that provides them cover and the insect species they rely on for food.
Deer promote the spread of invasive plant species by transporting the seeds on their coats, hooves and in their feces, eliminating competition from native plants and disturbing soils. As our forests are oversimplified we lose native species, and once the existing trees die, there will be little to replace them except the few native species that deer find unpalatable and non-native species that provide little ecological benefit.
In 2008 the USDA Forest Service began to make dire predictions about eastern forests due to the over-browsing by white-tailed deer. The problem is so severe that even if we could reduce the number of deer immediately to within ecologically sustainable levels, it would take many decades if not centuries to recover our native plant communities.
If we act soon we can retain enough native plant stock and seed that many species could recover within remaining forests and repopulate surrounding areas over time.
This is even more critical in the face of climate change in the expected shift of species and communities across the landscape.
So what are we to do about it? Forest management professionals, advocating for the sustainable use and management of forest resources were clear: “To do this, white-tailed deer populations must be low enough to allow for the regeneration of forests and the development of desired plant communities and wildlife habitats.”
To reduce the number of deer, people generally raise the prospects of reintroducing large predators, sterilizing deer or administering birth control to curb population growth, and using lethal control methods to include hunting and sharpshooting.
Lethal control methods are the only deer population control option that have been shown to be effective. It is time for residents and local governments throughout Virginia to join with the Virginia Department of Game and Inland Fisheries, the Virginia Natural Heritage Program, large landowners and managers and others in supporting and urging efforts to reduce and manage the number of white-tailed deer in order to protect our native plant species, the communities in which they live and the animal species that depend on them.
The conversation needs to shift from deer to plants. We need to have fewer deer so we can have more of everything else – more native plants and the myriad of organisms they support. I would rather share the land with a diverse assemblage – see trailing arbutus, thimbleweed and lady-slipper orchids; hear the call of ovenbirds.
Source Document: Whitetail Deer in Northeastern Forests: Understanding and Assessing Impacts, USDA, November 2014 NA-IN-02-14_WhitetailedDeerNEForestsWEB