Surging Deer Populations Are a Crisis for Eastern Forests

An easy 10-minute walk from Rheinstrom Hill Audubon Sanctuary and Center in upstate New York, a visitor can pause and take in two distinct forests. On the right side of a winding trail, the woods are lush. Crimson tips of sumac peek above a tightly woven bouquet of young oak, hickory, and aspen, and a tangled understory of blackberry and witch hazel conceals rummaging towhees and mewing catbirds. It’s a messy barrage of green, practically throbbing with life.

Not so on the left side, where the trees stand far apart, like the remains of a half-used matchbook. Here the eye travels easily to the horizon, past barren stems poking up from a thin carpet of dead leaves. Even at the height of summer, this area is brown and eerily quiet, its silence broken only by the occasional knocking of a woodpecker. The difference between these two stands of woods? Deer.

As most anyone with a backyard garden can attest, there are a lot of deer sauntering around the United States these days. In suburban areas, it’s common to see deerproof cages wrapped around trees or dead deer crumpled on the shoulder of a road. One car dealership in northeast Ohio marks “collision season” with its deer-for-steer deal, offering 20 pounds of beef to customers who bring in their deer-damaged vehicle for repair. Many cities and towns take a more tactical approach: Sharpshooters set out after dusk, armed with silenced weapons and a mandate to thin ever-growing herds.

White-tailed deer are the most widespread and familiar deer species in the United States. While conversations about their overabundance typically center around suburban landscapes, there’s growing recognition that too many deer can jeopardize the health of forests, too. They provide easy transportation for invasive species and disease-carrying ticks, and their prodigious munching reduces the forest’s ability to store carbon. More worryingly, overbrowsing decimates the shrubby understory and prevents seedlings from growing into new trees, threatening the future of the forest itself.

Not just the plants suffer; so does every creature that relies on them. One study in Pennsylvania found that when high densities of deer roamed a forest, the abundance and diversity of birds that use midstory vegetation plunged by 37 percent and 27 percent, respectively. Five species were extirpated from the study area when deer density reached 20 or more animals per square mile.

Eight years ago, deer density at ­Rheinstrom Hill hovered around 45 per square mile. That’s when staff at the ­Hudson Valley sanctuary removed old trees to generate new growth and erected a polypropylene fence around a 2.5-acre plot. They hoped that by excluding deer, they could grow a young forest, something the 1,000-acre preserve lacked—and along with it bring back the birds that nest, hide, and forage there.

But what appeared inside the fence, and how quickly it appeared, surprised even the staff. “The Chestnut-sided ­Warbler, Eastern Towhee, and Indigo Bunting—those popped up almost immediately,” says David Decker, a land steward for Audubon New York. Seven years later, more surprising visitors arrived: Black-throated Blue and Black-throated Green Warblers, birds that had never been observed in the sanctuary. “Even though there was 1,000 acres of forest, it wasn’t healthy enough,” Decker says.

The birds were just the start. Decker and his colleague Suzanne Treyger, the group’s senior forest program manager, watched in amazement as myriad native trees sprang from the soil: sassafras, sumac, and multiple kinds of maples and oaks—at least 13 species in all, almost double those found in the rest of the woods. “This is what the forest should look like,” Treyger says, gesturing toward the verdant, fenced-in plot.

Yet very few forests in the Northeast do. When it comes to the many threats facing eastern forest birds, which by some counts have declined by 30 percent since the 1970s, Treyger says whitetails loom large: “We list deer right up there with climate change.”

Most of the region’s woods are about the same age, having taken root around the time Americans ditched their farms and migrated en masse to cities in the late 19th century. As those forests matured, white-tailed deer, once nearly hunted to extinction, staged an impressive comeback. Their success has slowly ­morphed into an intractable crisis.

“The forests of the Mid-Atlantic and Northeast are in imminent danger of collapse,” says Cornell University ecologist Bernd Blossey. “And there is little hope that business as usual or incremental changes will suffice to address the ­serious issues we face.”

While conservationists and land managers scramble for solutions like fencing, advocates like Blossey are calling for a more ambitious approach: marshaling the power of the federal government to address what has become a national emergency.

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or millennia, Indigenous tribes coexisted with and relied on white-tailed deer for food, clothing, and tools. Estimating deer populations is more art than science, but the National Park Service figures that eastern woods hovered around 8 to 11 deer per square mile prior to European settlement.

In an intact ecosystem, deer populations are held in check through predation, disease, and food availability. But settlers quickly dismantled healthy forests, clearing the land for timber and agriculture and slaughtering deer for hides and venison. By 1890 an estimated 300,000 ­whitetails roamed the entire country. You’d have been hard-pressed to find a single deer in the Hudson Valley.

Few Good Options

Ballooning deer herds degrade forest habitat while also placing people at risk. To curb populations, officials around the country are choosing from an arsenal of imperfect solutions.

Professional Removal 
Many towns opt to manage deer by hiring professional sharpshooters. The approach is effective: One suburban study showed it resulted in significantly fewer deer-vehicle collisions. The American Veterinary Medical Association approves the method as a humane form of lethal control, and it’s relatively inexpensive at $200 to $400 per deer. But many residents oppose culling efforts, citing concerns over animal welfare and public safety. Although opponents unsuccessfully sued to get sharpshooters out of Rock Creek Park in Washington, D.C., the density of native plant seedlings nearly tripled after less than a decade of culling. 

Fertility Control
Where public safety or politics make sharpshooting unfeasible, some officials are trying fertility control. In a Cincinnati, Ohio, neighborhood, a sterilization program has reduced the deer population by 30 percent in 5 years. But fertility control, while more acceptable than hunting to animal lovers, comes at a steep price: more than $1,000 per deer on average. In Staten Island, New York, where hunting is illegal, officials have spent nearly $6 million on deer vasectomies to cut down the borough’s herd by almost a third. 

Predator Reintroduction
Because the extirpation of wolves, mountain lions, and bears is one reason deer numbers soared, reintroducing predators to control populations seems logical. For obvious reasons, though, it’s far from palatable in urban and suburban areas and has yet to be attempted. Furthermore, in places where predators have rebounded naturally, their ability to keep herds in check is still up for debate. When deer harvests plunged in Michigan’s Upper Peninsula, hunters blamed a growing population of gray wolves. State biologists, however, argued that land-use changes and harsh winters were responsible for the crash. Coyotes are significant deer predators, but a 2019 study covering six eastern states found that they don’t kill enough whitetails to reduce populations. 

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Then all at once, the cervids’ luck changed. Deserted farms began to sprout forests, while startling declines in wildlife triggered a cultural reckoning—and the modern conservation movement. By the early 1900s the federal government had banned market hunting; game wardens were patrolling the woods to enforce new hunting laws; and a number of sportsmen’s organizations and nascent state game agencies began releasing ­captive-raised deer back into forests. After settlers had spent centuries wiping out predators like wolves and mountain lions, those woods were now a veritable haven for deer. As a result, whitetail populations exploded over the next few decades. Today there are estimated to be more than a million in New York State alone.

The impacts of deer overpopulation can be difficult for the average person to notice; chipmunks still scurry about, and sunlight still streams through the canopy. To a forester, the devastation is more obvious: the lack of species diversity, the prevalence of invasive plants, the stunted seedlings. In his 1949 essay “Thinking Like a Mountain,” famed naturalist Aldo Leopold looked out over a deer-laden landscape and saw “every edible bush and seedling browsed…every edible tree defoliated…as if someone had given God a new pruning shears, and forbidden Him all other exercise.” Leopold suspected the damage would transform the forest and persist well into the future. He was right—and roundly ignored.

Fifty years after Leopold published his essay, another forester was growing dismayed by the denuded woods in his charge. Since 2000, as director of Cornell University’s 4,200-acre Arnot Teaching and Research Forest outside of Ithaca, New York, it’s been Peter Smallidge’s job to maintain the storied forestry program’s “outdoor laboratory.” But a few years into his tenure, Smallidge noticed that seedlings in the Arnot were rarely growing above ankle height.

In 1998 the Arnot, which had allowed hunting for decades, launched the Earn-a-Buck program. The initiative aimed to thin local herds by offering hunters an incentive: kill two does and earn the privilege to shoot a buck. “We had really significant harvests,” Smallidge reports. “Long story short: It didn’t have any effect.” There were just too many deer for the program to make much difference. Still, Smallidge says staff hadn’t fully grasped the scale of the problem until 2004, when it was time to perform regeneration treatments in portions of the Arnot—or, as Smallidge puts it, “replace the current forest with the next forest.”

In essence, regeneration treatments activate the natural life cycle of the woods, known as forest succession. This happens without human intervention, too, when a wildfire, severe storm, or other significant event takes down a swath of trees, allowing sunlight to reach the forest floor and new plants to grow in their place. Each phase of succession supports different birdlife, from meadowlarks during the early, grassy stage to owls and Ovenbirds in the old-growth years. At any time, the forest can experience another disturbance, kickstarting the process all over again.

But that year and the next, regeneration efforts at the Arnot failed. Seedlings popped up, but so did whitetails, making quick work of them. Almost as alarming as what the deer ate was what they didn’t. Like kids picking out marshmallows from bowls of Lucky Charms, deer tend to feast on the trees that foresters (and certain birds and insects) desire most and to leave behind the stuff that nobody wants.

“We grew back a forest, but it was the wrong kind of forest,” Smallidge says. The new trees, while native, had become unnaturally dominant, and each had its drawbacks. Hornbeam and striped maple, for example, don’t grow tall or produce good timber. Things were no better closer to the ground, where deer have been found to avoid—and therefore give a competitive advantage to—certain invasive plants like Japanese ­barberry and garlic mustard.

Smallidge was bereft but resolved. “As director, the legacy I leave behind was not going to be an impoverished forest,” he says. Hunting wasn’t working, and fencing, while gaining in popularity, would be difficult across the Arnot’s remote acres. Monitoring and maintaining miles of polypropylene fence would suck up valuable hours of staff time.

That’s when Smallidge and Arnot forest manager Brett Chedzoy had an unorthodox idea. Regeneration treatments produce a lot of slash, the commercially inviable trunks and treetops left behind after logging. Maybe, they thought, instead of just leaving it on the forest floor, they could use the slash to construct a shaggy but formidable barrier.

In 2017 the first slash walls went up at the Arnot. Piled 10 feet high and 20 feet deep, the walls enclosed 70 acres of recently logged forest. To address the legacy effect of deer—the abundance of undesirable seedlings in the plot—the logging crew “brushed the understory,” Smallidge says. “The equipment they use is like something out of The Lorax. It was very barren after they were done.”

But not for long. Six years later, on a bright day in late July, Smallidge stands buried to his waist in green. It’s the most diverse forest he’s grown in his 37-year career and something of a wake-up call; pressure from deer had warped his sense of how multifarious the woods could be. “The next forest is in place,” he says, delighted. As a pair of Cedar Waxwings swoops overhead, he sounds like a teacher calling roll: “We’ve got big-toothed aspen, quaking aspen, sugar maple, sweet birch, red oak, white pine. It’s a real mixture of species; you don’t see that anywhere.”

The slash walls weren’t built with birds as the focus, but a surge of avian life is among the most obvious signs of their impact. Every spring, Treyger leads a bird walk in the fortified forest. “The young forest birds in there—it’s deafening to hear how many are singing,” she says. “It’s just fantastic habitat that they’ve created.”

The Arnot now has 27 walls protecting 500 acres. Smallidge has become something of an evangelist, touting their ability to produce valuable timber and provide habitat and hunting grounds to mammals like foxes, fishers, black bears, and bobcats, which can clamber over or through the walls. More than 1,000 people—foresters, park managers, and private landowners—have come to the Arnot to view the slash walls, resulting in projects in seven other states. “This,” Smallidge says, beholding his healthy new forest, “is the success of my career.”

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espite their growing popularity, fences of any kind aren’t a panacea. They’re more like a personalized treatment plan at a premier hospital: great for those with the time and money. According to Cornell’s figures, slash walls cost $1.47 per foot, while plastic barrier fencing costs roughly three times as much. And both types have drawbacks: Polypropylene fencing is prone to damage and needs frequent maintenance. Slash walls require a fleet of laborers and heavy machinery. They are also temporary, as they slump about a foot a year; while they give the forest time to regenerate, within seven or eight years deer find their way back in. And fencing of any kind fails to address the larger question: What is to be done about all these deer?

It’s a controversial topic, as local officials from Staten Island to the Olympic Peninsula are finding out. Deer are responsible each year for more than $100 million in agricultural losses and traffic accidents estimated to cause nearly 60,000 injuries and more than 400 deaths. Where public consensus is possible, controlled hunting and sterilization programs have been the most popular management strategies. But while there have been isolated successes, neither option has proven reliably effective. In short, there aren’t enough hunters to have a significant impact on populations, and sterilization programs can be prohibitively expensive.

Treyger recognizes that the debate over solutions is “a tricky one.” Still, she says, the time to act is now: “So many of our forest birds are declining and some of them so significantly, we can’t wait.” The Cerulean Warbler, for example, has seen a 63 percent population decline over the past 50 years. The songbird prefers to nest in white oak, a tree species highly prized by hungry deer.

Like Smallidge, Treyger and Decker have been showing their fences off to visitors. In New York, 75 percent of forests are private, and the pair are hopeful their project can inspire guests to deerproof their own backyards. “We know we can’t fence everything. We can’t build slash walls everywhere,” Treyger says. “You might not be able to do 100 acres, but a 6-acre cut has been shown to make a difference. We can still have a big impact on the landscape.”

Blossey, the Cornell ecologist, doesn’t disagree—he has installed deer exclosures on his own 350-acre property outside of Ithaca—but he has a less rosy outlook about relying solely on local solutions, fearing they are too scattershot and too fragmented to make a difference. “We need to fundamentally overhaul how we make decisions,” he says. “We need ­federal ­leadership.”

When reached for comment on the federal government’s approach to deer, the U.S. Fish and Wildlife Service deferred to the U.S. Department of Agriculture. A USDA spokesperson subsequently referred questions about deer overpopulation to the FWS. Both agencies declined to comment.

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lossey never meant to study deer. The ecologist spent many years working on invasive plant management until “deer forced themselves onto the agenda.” It was impossible to study one without the other. Now he believes out-of-control deer populations belong high on the list of threats to forest health: “There cannot be any conservation in the United States without considering big herbivores.”

That’s why he’s begun advocating for a more integrated approach to the deer problem—one that’s not siloed among state departments of natural resources, but spearheaded by federal agencies responsible for wildlife, human health, transportation, and agriculture across interstate boundaries. Only the U.S. government has the clout to solve the problem, he and his coauthors argue in a recent paper.

Blossey’s idea may be a new approach to deer, but hardly a new response to a widespread ecological crisis. The federal government has played a primary role in a number of conservation emergencies. For example, the North American Waterfowl Management Plan was developed in response to crashing waterfowl populations in the 1980s. It requires the FWS—in partnership with tribal governments, ­Mexico, and Canada—to monitor bird populations and set harvest limits, while the states use those guidelines to determine their own bag limits and seasons. The program has largely been successful, and waterfowl are one of the few groups of birds in the United States not in dramatic decline. Elsewhere, the FWS and the USDA have spent decades removing thousands of invasive nutrias—voracious, semiaquatic rodents—from the Delmarva Peninsula in an attempt to protect vanishing marshlands.

Effective deer management, Blossey argues, will demand long-term investment and test public attitudes about the ethics of widespread culling. That’s because a national strategy will also require a ­substantial reduction in deer herds, at least at first. “There’s no hope for ­anything else other than lethal control,” he says. That should involve a ­coordinated, ­research-driven process funded, ­measured, and managed by the federal government, Blossey says, not left to individual states, cities, and property owners to figure out for themselves.

As if his proposal wasn’t controversial enough, Blossey maintains that the only way to thin herds sufficiently to fix the problem is by bringing back regulated market hunting, in which private entities kill and sell wild game—a practice that is currently illegal and flies in the face of the widely embraced North American Model of Wildlife ­Conservation. However, many deer-culling programs already provide venison to nearby residents and local food ­pantries, a practice that could be implemented on a nationwide scale to reduce hunger as well as reliance on cattle farming, a big contributor to greenhouse gas emissions. Deer will die regardless, he argues, either by human hands or, as Aldo Leopold once predicted, from disease and starvation brought on by “their own too-much.”

Despite the grim choices before us, Blossey feels hopeful about the future of American forests and the creatures that live in them. “There’s so much resilience built into these things,” he says, looking out over the wooded valley beyond his back porch. “Think about what has happened here: pollution, plowing, clear-cutting, acid rain,” he says. “With everything that was done to these woods, there were very few extinctions in the entire ­Northeast. It’s incredible to think about it.”

If eastern forests are to survive yet another existential crisis, it will be because people choose to act, whether through local initiatives or federal action. “It was us who messed up this system,” Blossey says. “It’s our job to fix it.”

This piece originally ran in the Summer 2024 issue as “The Buck Stops Here.” To receive our print magazine, become a member by making a donation today.