Gifford Garden Notes
Just what can be done to lower (and maintain) deer densities to levels where their impacts on forest ecosystems are minimal?
by Brad Roeller
Just what can be done to lower (and maintain) deer densities to levels where their impacts on forest ecosystems are minimal? In the last couple of decades, much research has been directed to addressing questions concerning optimal population levels, and methods of achieving these levels. Through controlled experiments utilizing deer enclosures which simulate different deer densities, it is now believed that deer populations in the range of 10 to 20 deer per square mile will minimally impact, or not impact at all, forest ecosystems. Remember, that in the Hudson Valley densities of white-tailed deer average 45 per square mile. How do we get to this optimum deer population? Well, there is no easy answer, but there is reason for hope.
An enlightened approach to managing a forest is to look at the whole ecosystem of the forest and develop a management strategy by which the full array of forest values and functions is sustained at the landscape level over long periods of time. In many areas of the country, deer are positively valued as both an economic and recreational resource. In 1991 there were over 10 million hunters in the US who spent over $5.1 billion dollars on travel and equipment associated with hunting and photographing white-tailed deer. Lowering deer populations to suggested levels would have considerable impact on this powerful group of forest resource users. However, all forest resources should be managed to produce "simultaneous sustained yield of many interrelated populations in an ecosystem". Simply put, to sustain multiple resources, including deer, requires that management for each individual resource be compatible with that of others. Managers of forests, and practitioners of ecosystem management, where it requires reducing deer density, must be prepared to address and counter political and social pressure that will resist such action (deCalista, 1992).
Just what are the options for reducing deer density? Well, many suggest, "why not trap the deer and relocate them to areas where they won't do harm?" Unfortunately, this has proved both impractical and harmful to the deer. One study documented 85% mortality of relocated deer one year after their release. Biologists have identified a disease, capture myopathy, linked to this delayed mortality in trapped and translocated deer. Additionally, the costs associated with this technique range from $400-$2,931 per deer.
Lethal methods of reducing and controlling deer populations have yielded mixed results. Trapping and euthanasia has proven inefficient and expensive. Sharpshooting programs have been employed in several communities in the northeast where experienced personnel lethally remove deer. A variety of techniques can be used in sharpshooting programs to maximize safety, humaneness, discretion, and efficiency.
Controlled hunting is the application of legal, regulated deer hunting methods in combination with more stringent controls or restrictions as dictated by landowners or elected officials. IES has run a controlled hunt for well over 20 years as part of an internal management program to maintain deer densities within acceptable levels. Wildlife biologist Ray Winchcombe, utilizing an integrated approach to monitoring and assessing the local deer herd, targets (no pun intended) the desired number and composition of the annual deer harvest. However, resolving the inevitable conflicts associated with lethally removing large numbers of deer, either through a sharpshooting program or controlled hunts, is an ever-present challenge to communities and wildlife managers.
Perhaps the best hope for managing local deer populations in large areas will lie with the experimental fertility control agents utilizing contraceptive vaccines to regulate free-ranging deer populations. After 4 decades of research, effective antifertility programs for controlling populations simply do not exist. Research continues concentrating on steroid contraception drugs, immunocontraception (agents which stimulate the production of antibodies against proteins and hormones essential for reproduction), and with contragestation. Costs, delivery methods, and the oversight of the FDA (as all these drugs are classified as experimental, hence subject to Federal oversight), means that research needs to continue.
Many researchers feel that oral applications of antifertility agents, utilizing bait stations, will be the best chance for managing deer herds in large areas. Obstacles such as dosage control, absorption of active ingredients, and the ingestion of bait by non-target wildlife, all have to be dealt with. According to experts in this field, we are perhaps 3 to 5 years away from developing a single-dose oral contraceptive.
Unless steps are taken to address the issue of high deer populations and the associated impacts on our forest ecosystems, continued high levels of deer herbivory may cause irreparable damage to our local forests. These steps can range from simply opening up your property to deer hunters, to promoting multi-faceted, community-based initiatives to maintain an optimal population of deer in your region.
Next week: The calendar says spring!
Gifford Garden Archives, January 2003 - present
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