Eating Themselves Out of House and Home
In some areas, exploding populations of white-tailed deer are obliterating layers of woodland habitat; is there a solution
- Frank Kuznik
- Oct 01, 1998
Scattered clumps are all that remains of the first snowfall in northern Ohio, diminutive pockets of white dotting the woodlands of the Cleveland Metro- parks. Inside a conference room at park headquarters, wildlife biologist Tom Stanley looks wistfully out the windows and imagines a harsher climate, one that would provide a ready solution to a difficult problem.
"Up in Minnesota, they get snow this time of the year that stays on the ground until spring, packed four or five feet deep," he says. But in Ohio, "even in our worst winters, the deer can paw through to grasses and shrubs. You just don´t get significant die-offs."
Not that Stanley has anything against deer. In fact, as chief of natural resources for the parks, he´s charged with protecting them. But a seasonal thinning of the herd would help him remedy a situation faced by a growing number of wildlife managers: too many white-tailed deer.
In forests throughout much of the country, and particularly in parks and reserves in the East, white-tailed deer are at record population levels. "We´re seeing 30, 40, even 60 deer per square mile almost everywhere now, compared to the 10 to 12 or fewer deer per square mile we believe were here pre-European settlement," says Donald Waller, professor of botany and environmental studies at the University of Wisconsin-Madison.
Historically a boom-and-bust species, deer are the beneficiaries of a severe drop in predators, such as wolves and mountain lions, and an explosive growth in "edge" areas bordering their woodland habitat--especially suburban backyards brimming with tasty gardens and shrubs. Freed of natural constraints, deer are having a substantial, and in many cases adverse, effect on plants and other animals. They are eating certain trees and shrubs into near oblivion in some areas, in the process obliterating whole layers of habitat.
"I see it as being a very widespread and major problem," says Robert Warren, professor of wildlife ecology and management at the University of Georgia. "There are places that overbrowsing by deer has created situations where, even if the herd is reduced, it may not be sufficient to allow the area to restore itself to its natural state."
In portions of the Cleveland Metroparks (and adjacent Cuyahoga Valley National Recreation Area) heavily populated by deer, a number of once-common shrubs, vines and flowering plants--woodland asters, goldenrods and rarer species such as trillium and fringed gentian--are in serious decline. Sumacs, stripped of their bark by hungry deer, are rapidly disappearing. Jewelweed, an important food for small birds and mammals, is virtually gone. In some areas, tree seedlings have been browsed so intensely that forest regeneration has ground to a halt.
As a result, both plant and animal species are vanishing from the ecosystem, according to a 1997 vegetational survey of the Cleveland-area parks. Food and cover for many ground-nesting birds and small mammals have disappeared, the report notes. Several small animals, such as chipmunks, are now seldom seen along the trails and bike paths.
A local task force concluded that the most effective way to prevent further damage would be using sharpshooters to remove about 570 deer (from a 1997 population estimated at 8,000, about 37 per square mile). Though relatively small, that number would thin out the most densely populated areas, giving plants and animals there an opportunity to recover. Additional deer harvests would further reduce the population to a projected carrying capacity of 10 to 30 deer per square mile.
Deer culling is not new; park managers from Connecticut to California have used it, often after fencing, relocation or birth-control programs proved impractical. Relocation and fencing are often prohibitively expensive. Birth-control programs, which call for repeated innoculations, are difficult to administer effectively to free-ranging herds. In addition, Stanley points out, government officials have been reluctant to grant approvals for either deer relocation or birth control.
Given the lack of viable alternatives, experts say that hunting is the appropriate choice. "With the absence of large predators, hunting has been the most effective method to keep populations in check," says Doug Inkley, senior scientist for the National Wildlife Federation.
But shooting deer is frequently controversial. In northern Ohio, the hunt was prevented last winter by a court injunction obtained by In Defense of Deer, a grass-roots group opposed to shooting deer for any reason. "It´s not a deer problem, it´s a people problem," insists Bonnie Vlach, founder and president of the group. "People move into these posh developments alongside the park, then start complaining when the deer come out and eat their shrubs. If you just leave well enough alone, the system will regulate itself."
Stanley disagrees on both counts. "We´re not suggesting we need to reduce the deer population because there are too many in people´s backyards," he says. "The issue is the damage to the Metroparks, which is so drastic we´re losing significant biodiversity. If we let the population go, I think there´s ample evidence that the damage will be so great, the forest ecosystem will not recover in a normal person´s lifetime."
A nightmarish realization of that scenario lies just 150 miles south, in Sharon Woods, a one-square-mile park in the Columbus area. The deer population there grew from zero in the early 1970s to about 500 in the early 1990s, with devastating results. "We called Sharon Woods an ecological desert," says Larry Peck, assistant director of Franklin County Metroparks. "From a height of six feet down, there was nothing but deer and pawpaws, a native plant they don´t like. They ate everything else, even the bark off the trees."
Wildflowers, once a noted attraction in the park, vanished, as did most of the ground cover--a total of more than 150 plant species. Bereft of habitat, small mammals, reptiles and ground-nesting birds fled. "Basically, anything that lives in the understory was gone," Peck says. "Butterflies, insects--you name it." Even predators such as owls disappeared.
A combination of birth control, relocation and hunting efforts have since reduced the deer population in Sharon Woods to about 40, and some wildlife and plants are coming back. "But my resource managers tell me that ultimately, if we want all the native plants back," says Peck, "we may have to reintroduce some ourselves."
Sharon Woods is an extreme case. Typically, far fewer deer impact a number of preferred plant species gradually, over a period of years or even decades. Those changes can be subtle and hard to track. "It´s very difficult to study deer browse on herbaceous species, because if the deer have eaten something, it´s gone," says Waller. "It doesn´t leave an historical signature, the way a browsed tree seedling might."
Waller found revealing study sites on the Apostle Islands in Lake Superior, only some of which have deer. "We were concerned about some species of lilies and orchids being browsed to extirpation. And indeed, that´s what our study turned up," he says. The bluebead lily (also known as Clintonia), for example, disappeared when there were more than 12 to 14 deer per square mile. Another species, Canada yew, grows thick on the islands without deer, but is virtually nonexistent on those with them. Nor are such losses confined to the islands.
"Yew has pretty much disappeared in the upper Midwest except on Indian reservations, steep cliffs and in the Lake Superior snowbelt--places deer have a difficult time getting to, or in the case of Indian reservations, are regularly hunted," Waller says. "We´re also seeing browse-sensitive tree species, like hemlock and northern white cedar, dropping out. Most mixed hardwood stands are going to pure sugar maple."
Even in large contiguous woodlands, where there are more opportunities for seeds to spread and grow, the loss of tree species can be dramatic. Overbrowsing in the Allegheny forests of northwestern Pennsylvania has transformed large areas of mixed hardwoods into a near monoculture. "At lower densities there´s still a good mix of trees, but once you get above 40 deer per square mile, they´ve basically eliminated almost everything but black cherry, which is hard for them to digest," says David deCalesta, a research wildlife biologist at the Northeastern Forest Experiment Station in Warren, Pennsylvania.
DeCalesta recently returned to a colleague´s study sites from eight years earlier to document the effects of habitat loss on songbirds. He found no difference in bird populations in the upper canopy, where deer can´t reach. On the ground, biodiversity has shrunk dramatically--some 50 species, including Jack-in-the-pulpit, red elderberry and hobblebush, are gone, replaced largely by ferns. But the remaining vegetation is still thick enough to house ground-nesting birds.
In the mid-canopy, however, deCalesta found that the number of bird species had declined by 27 percent, while the total population dropped by more than a third. "In areas of high deer density, there´s a big hole in the mid-canopy," he says. "While there´s still enough habitat for some birds, for others there´s no nesting or feeding structure left."
How far the effects of overbrowsing ripple through the ecosystem has yet to be fully measured. But as the number of studies grows, so does the apparent impact. In Illinois, Michigan, Maryland, Kentucky, New Hampshire, Georgia--almost anywhere scientists have examined the ecological damage done by deer--they´ve added to the list of plant species being adversely affected. This comes as no surprise to Warren.
"The plant community is the basic foundation of an ecosystem," he explains. "If you alter that, you´ve altered the very basis of production, and that reverberates up and down the food chain. Any level of the ecological community, even invertebrates, can be affected."
Do those effects justify managing deer? Some citizens´ groups say no, because they find the animals endearing or, like Vlach, believe that human encroachment on wildlife habitat is the real problem. But even some scientists who acknowledge the ecological impact of deer are not convinced the answer is always yes.
"I don´t think we have firm evidence yet that lower-diversity forests are functioning any less well than they were before we had high deer densities," says Bill McShea, a research scientist at the Smithsonian Conservation and Research Center in Front Royal, Virginia. "If you have something in your park that´s the last population of this or that, then fine, get rid of the deer. But that´s a value judgment. In most forests, I think we can afford to wait and see how this comes out."
Waller, for one, is not willing to take that risk. "We know very little about the rates of recolonization of some of these herbaceous plants," he says. "If you eliminate all the bluebead lilies, we don´t know how long it will take that population to bounce back--it could be 10 to 20 years, or 150 to 200. Until more research is done, we can´t even speculate what the long-term effects will be."
Warren believes that some areas, such as the Allegheny Plateau, have been overbrowsed for so long they´ve reached an "alternate stable state," in which the natural succession of species--those that would flourish under normal reproductive and climatic conditions--has been permanently supplanted by a lower, less diverse order.
"When you´ve got a situation in a northern deciduous forest where the deer chronically nip off tree seedlings, over decades you can totally exhaust the seed source," he says. "There´s nothing left to regenerate the natural species."
But forests are always changing, with or without deer--and deer are notorious for their cyclical population swings. Given that, some critics say the smartest strategy would be to do nothing. "Let nature take its course," urges Vlach. "Whenever we get in there and try to control things, we make them worse."
"Generally speaking, I agree with that," responds Stanley. "But we´ve already tampered with the system by removing the predators, allowing another species to grow way beyond what it´s supposed to. Left alone, yes, something will eventually knock back the deer population. But we´ll be left with an ecosystem significantly different from the one we had."
Can ecosystems recover from the damage inflicted by deer? Perhaps, if people reduce the deer herd and then replant or reseed the area, says Warren. "The question is," he says, "should we wait until such dramatic and costly measures are necessary?"
Frank Kuznik recently relocated from Cleveland to Seattle, where the backyard opportunists are more likely to be coyotes than deer.