This column originally appeared in the September 16, 2007 issue of the Poughkeepsie Journal.
White-tailed deer are one of the most visible wildlife species in the Hudson Valley. Despite the pressures of human development and habitat loss, deer populations are flourishing throughout our region. As our forests become more fragmented, managing deer becomes increasingly difficult. Left unchecked deer overpopulation can have a range of negative impacts on forest ecosystems.
Healthy forests have four layers of vegetation, beginning at the ground level with grasses, wildflowers, and seedlings. Shrubs and small saplings make up the second layer, while larger saplings comprise the third. The fourth layer consists of mature canopy trees. Combined, these layers make up a forest's vertical structure. The habitat diversity contained within this structure is essential to an array of wildlife species, including songbirds, owls, hawks, small and medium sized mammals, insects, and amphibians.
When deer herds are well-balanced, a forest's vertical structure thrives. A person standing in a healthy forest would have a difficult time looking through the trees. Ground cover and low-lying vegetation is lush and the forest is bustling with plant and animal life. When deer numbers escalate, vertical structure is literally consumed. Deer reduce or eliminate vegetation below six feet in height— the farthest their hungry mouths can reach— leaving behind a desolate understory.
The loss of low-lying vegetation comes at a high price for animals living in the forest. Shrubs, saplings, and herbaceous plants provide important nesting, feeding, nursery, and escape cover to many forest dwelling birds, mammals, amphibians, and insects. The reduced state of plant complexity also works against the deer themselves. Scarce food resources cause a decline in deer health, and fawn mortality increases due to a reduction in adequate escape cover.
Deer are selective feeders that focus their efforts on plants that appeal to their palates. Unfortunately, this behavior reduces plant species diversity. When deer numbers are high, plants like trilliums, lilies, and wild orchids seldom survive. Young saplings are also preferentially eaten. As a result, over-browsing by deer can prevent the regeneration of desirable timber and acorn-producing trees like oaks, resulting in a loss of both wildlife food and timber resources.
Through their dietary preferences, deer can shift a forest's balance from native to introduced exotic species. Hay-scented fern, garlic mustard, Japanese barberry, honeysuckles, and ailanthus tend to thrive when deer numbers are high because they are less palatable to deer and they have no local pests or diseases. When these species dominate the forest understory, they can inhibit the establishment and survival of native tree seedlings; over time this can shift the tree composition in a forest.
If deer over-browsing is left unchecked, the forests of the future will look very different from those of today. Plant diversity will likely be dominated by invasive exotic species that afford little value to wildlife and are useless as timber products.
Deer management in New York State is overseen by professional wildlife biologists who are guided by science-based principles of ecology and management. Their goal is to balance deer populations in a way that yields a healthy forest ecosystem while being sensitive to the desires of society. In the case of deer management, the principles of wildlife biology and ecology, not politics, should determine local deer numbers. This approach will ensure the long-term sustainability of our forested ecosystems. The alternative to sound management is biodiversity loss, which leaves us all impoverished.
Stay informed, and be a voice for habitat-based deer management. Remember, when our forest ecosystems deteriorate, wildlife suffers, and poor habitat means less wildlife— for everyone.
Ray Winchcombe is a wildlife biologist at the Institute of Ecosystem Studies in Millbrook, NY. |
