Bambi Must Die

The case against Minnesota's 1.2 million forest-destroying, disease-spreading deer

But the truth is, even where they are below the social carrying capacity--there are still a few corners of the state where this is true--deer do plenty of damage. It is damage that is much harder to see than a ruined vehicle or wrecked suburban garden but also far more invidious. In fact, a growing body of evidence suggests that our overabundance of hungry whitetails is causing significant, potentially irreversible harm to forest ecosystems. The case against the whitetail doesn't end there. The rising number of deer is also implicated in the spread of Lyme disease, now the most common insect-borne disease in North America.

There is a nasty list of indictments to be brought against our gentle friends of the forest and it leads to an avoidable verdict: Friends, Bambi must die.

In the mid-1980s, Don Waller first began thinking about the harm deer might be doing to the plant communities in hardwood forests. A professor of botany and environmental studies at the University of Wisconsin at Madison, Waller had spent most of his career studying what he refers to as "noncontroversial things, like how plants have sex." But increasingly, his students were urging him to investigate the management--or as he puts it the "mismanagement"--of the national forests. In particular, Waller says, they pressed for more study of the ecological effects of wide-scale logging in the forests of Wisconsin and the Upper Peninsula of Michigan.

Going in, Waller understood what deer hunters and loggers have long known: Logging, especially as it has been practiced in the upper Midwest, creates ideal deer habitat. Whitetails, which wandered across the Aleutian land bridge to the New World 15 million years ago, are today an "edge species." In other words, it's a type of animal that prefers a forest with clearings (whether created by fire, blowdowns, or logging) to larger, unbroken tracts of old growth. As a result of land-management practices, whitetail densities have been increasing at alarming rates. A natural population for a hardwood forest might be between five and ten deer per square mile. But in some areas, Waller notes, Wisconsin has recorded as many as 58 deer per square mile.

When Waller started examining the plant communities of the national forests, he began rooting around the research literature for studies that addressed the effect all these deer might be having.

Despite a surprising dearth of information, it didn't take long for Waller to begin building a case against the whitetail. It just took a botanist's eye. In their surveys, Waller and his colleagues would identify the full-grown trees on a particular forest plot and then look for evidence of natural regeneration--in other words, seedlings. In areas with high deer populations, they discovered, the seedlings of tree species that deer like to eat (white pine, hemlock, sugar maple) seemed to be few and far between. In the areas with lower deer populations, the natural regeneration was more robust.

In Waller's view, the implications were obvious: The forest composition, at least as far as trees were concerned, seemed to be undergoing a significant transformation because of overforaging by deer.

Another important question remained. What was the expanding deer population doing to the most varied part of the forest, the understory plants? To get an answer, Waller referred to the work of John Curtis, a well-known figure in botanical circles for his comprehensive study of Wisconsin plants. During the 1940s and '50s, Curtis performed extensive plant censuses throughout the state, painstakingly recording the species and populations at various plots. Armed with Curtis's data, Waller and his fellow researchers returned to 62 of those sites, where they got on their hands and knees and recorded the exact numbers and types of understory plants they found.

"I expected there would be some changes, but I was surprised by the amount we saw," Waller recalls. Plants that were once common--mainly, grasses and sedges--had become even more common. But plants that used to be relatively rare--wildflowers, lilies, and orchids---had gone into marked decline.

The effects were most pronounced in places where deer hunting had been prohibited and populations had swelled. At Lake Gogebic State Park in the Upper Peninsula and Brunet Island State Park in Wisconsin, for instance, approximately 50 percent of the understory plant species that Curtis had recorded half a century earlier had entirely vanished. By contrast, in the few parts of Wisconsin where the deer populations had been kept low by acute hunting pressure, such as the Menominee Indian reservation, there was still plenty of plant diversity.

Waller looked for alternative explanations. Perhaps, he speculated, the differences were the product of natural growth cycles and varying levels of sunlight. In the end, no other hypothesis stuck. The forest understory was changing, Waller concluded, and whitetails were the main cause.

 

About five years ago, researchers from the University of Minnesota struck out for the western suburbs and began setting up deer "exclosures"--acre-sized plots of forest with 10-foot high fences to keep the deer out. After erecting the fences, the researchers let nature take its course.

Today, outside the exclosures, where the deer can get at the understory, the ground is still essentially bare--in effect, a biologically impoverished moonscape. Inside the exclosures, however, undergrowth has begun to come back. So far, nine plant species that had entirely vanished from the immediate vicinity have reestablished themselves in the deer-free area--evidence that recovery from the depredations of the whitetail is possible but slow.

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