Drastic Deer Damage Requires Drastic Deer Reduction

from the NY Times online, http://topics.blogs.nytimes.com/

By Emile DeVito

Land managers are aware of the catastrophic impact of super-abundant deer on tree regeneration and the loss of biodiversity in the metropolitan New York region’s herbaceous forest wildflowers. Now another phenomenon, the loss of the woody shrub layer, has reached a critical stage across most of the region (outside the New Jersey Pine Barrens). Above-ground stems of native forest shrubs are relatively short-lived compared with the life span of the rootstock. Vigorous new shoots replace older, senescent stems on a regular basis.

Deer now completely inhibit the establishment of new shoots, and older stems continue to die due to the normal aging process. Deer browsing results in a “crew cut” of dead basal shoots and exhausts the shrub’s root energy. This phenomenon is occurring in all native shrub species, from the upland Viburnums and Hamamelis (witch hazel) to wetland Lindera (spicebush) and Vacciniums (blueberries).

Right now in much of the metropolitan New York region, the last forest shrubs are within one or two years of death. As shrubs die, the absence of their leaf layer from the ground up to 12-18 feet allows the forest floor to become significantly more brightly lit. The extra light promotes the growth of alien invasive plants like Japanese stiltgrass (Microstegium). Without a shrub layer, alien invasive plants explode in density, gaining a strong foothold even under intact forest canopy.

But there is good news. In the Watchung Reservation, a parkland area in Union County, N.J., fencing that has kept deer out for 13 years has helped promote the regrowth of native woody trees and shrubs and perennial herbaceous plants in spots that had absolutely zero visible native plants in the understory when the fences — called exclosures — were erected in 1995.

These new areas of forest understory are dense and shade the ground, and they are suppressing invasive alien species that were abundant at the time of fencing. There is variation between plots; in some locations alien species are still common. But in every plot native species are now the dominant vegetation. In fact, in some locations — in the deep shade cast by native, regenerating trees — shrubs and wildflowers are outcompeting alien weeds!

It is clear that the only way to give our forests a chance to recover from both overbrowsing by deer and alien plant invasions is a two-step approach: 1. a drastic reduction in the deer herd, to a level so low as to achieve the functional equivalent of an exclosure (winter deer populations must be about 5 per square mile for a drastically damaged forest to begin to recover), and 2. the collection of local native seeds by local master gardeners or other volunteers, with associated gardening programs to re-introduce the native shrub layer where it cannot return on its own.

No field research needs to be done before initiating drastic deer herd reduction.

Collecting data sets filled with zeroes regarding plant regeneration is a waste of time and money. The deer population in the New York region needs to be driven down, way down toward 5 deer per square mile in order for our forests to begin a slow recovery. Research and deer censuses, fine-tuning for an optimal deer density under a forest recovery-based deer management program, can begin when the deer herd is approaching reasonable levels. Until native plants are regenerating in abundance, there is absolutely no reason to undertake the expensive task of counting deer.

Deer reduction can only occur with drastic changes to deer management, such as:

1. tax credits or other monetary incentives for every female deer (doe) harvested by an individual.

2. doe harvest requirements for landowners who receive a preferential, lowered property tax assessment for engaging in forestry programs that protect natural resources. Without aggressive management to reduce doe abundance, forestry programs have little chance of success in regenerating trees and other forest components. Deer fences may be substituted for hunting programs, where surrounding lands are not accessible to hunters.

3. economic incentives for municipalities and counties to initiate doe control programs.

4. legalizing the sale of local venison for food and hides for small manufacturing enterprises.

5. free butchering of deer for venison donations to homeless shelters.

6. other changes and innovations that represent thinking “out of the box.”

We are now stuck in the box of century-old fish and wildlife laws. These laws and rules were created when there were no deer, and the population had to be re-established with deer from the Midwest and the South, and then nurtured. Now, with suburban landscapes providing ample food during winter and cool-season agriculture providing abundant food by early March, no deer is ever stressed by winter, and all females bear at least twins by May.

This uncontrolled population explosion of deer has led to the conversion of our forests to a collection of alien weeds and vines in the understory, in which there is absolutely no reproduction of native woody trees and shrubs or herbaceous wildflowers. Our native forests and associated biodiversity will melt away, as can already be seen in many places, if we continue to ignore these threats.

Biodiversity is not the only natural resource at stake. Overbrowsed forests with only annual and biennial alien invasive weeds on the forest floor do not absorb rainfall as well as a healthy forest, resulting in more storm runoff, erosion, and siltation of water courses. Forests that have lost their layer of shade-tolerant shrubs and regenerating trees cannot store as much carbon as a forest that is filled with vegetation at all levels.

All nonprofit environmental groups, government agencies, sportsman clubs, farmers, professional foresters and community groups need to work together to reduce the regional deer population to a biodiversity-based carrying capacity, which must initially be significantly lower than 10 deer per square mile, but could be boosted to about 20 per square mile when the forest is once again filled with tree seedlings and saplings, a dense shrub layer, and a forest floor carpeted with wildflowers! But until we observe native vegetation rebounding and shading the forest floor from low heights of only 3-20 feet, we don’t need to waste limited resources by counting deer. Deer densities are so high right now that knowing their actual number is irrelevant to solving the problem.

If we do not pursue such a course of ecological forest restoration, future generations will consider our inaction to be an example of gross negligence in the management of natural resources.

Dr. Emile DeVito, a conservation ecologist, is Manager of Science and Stewardship for the New Jersey Conservation Foundation.