Science does underpin efforts to manage the deer population through hunting in every state. In practice, however, the science of deer management is no more immune to public pressure than is the science of stem-cell research.
At one extreme are those who object to killing animals on moral grounds. At the other are what might be called libertarian hunters. They remember forests abundant with deer over much of the last half-century and blame overzealous government biologists for producing today's comparative scarcity.
For their part, a broad consensus of scientists believes that for everyone's benefit, including the deer, hunters must adapt to a new role - as wildlife managers rather than just sportsmen - and game agencies must be willing to put up with the inevitable heat from constituents angry about their added civic responsibility.
The Pennsylvania Game Commission has been under intense pressure leading up to a coming vote on next year's hunting season. Some scientists outside the agency say the decision will indicate whether it is serious about thinning the deer herd before it further harms the forest. Some hunters say the vote will prove whether the commissioners believe in the state's heritage - and in them.
Deer management works by using hunters to mimic the effects of natural forces before civilization started meddling. Wolves and other predators, for example, used to kill large numbers of does and fawns trapped in the snow.
Even the trees were different - diverse in species and age - before man clear-cut the land a century ago, giving deer an all-you-can-eat smorgasbord that turned out to be a recipe for exponential growth.
In upstate New York, New England, and Canada, severe winters still periodically kill millions of deer. In Pennsylvania, New Jersey and states at similar latitudes, agencies that were formed around the turn of the century to bring deer back from near-extinction now are forced to control them to protect the rest of the ecosystem.
Besides hunting, available methods include contraception, fencing, trapping/relocation, and sharpshooting. All have been successful in specific, limited situations such as an island or a small park. None has proved feasible in deep woods.
With few predators, a well-fed deer herd can increase by 50 percent or more in one year. Indeed, a formula known as the exponential model shows that under optimum laboratory conditions, 10 females will grow to 4,076 deer in 10 years. (Bucks are serial breeders, so their exact number has little impact.)
Population change through lethal force is a simple matter of total births vs. total deaths. To reduce the herd exponentially, kill more does.
All states do this in one of two ways: They raise the number of permits for antlerless deer (mainly fawns and does). Or they increase the length of the antlerless seasons.
Unfortunately, most hunters prefer bucks. Many dislike killing females; some simply won't.
Repeatedly over the last 75 years, higher antlerless harvests have generated a hunter backlash, forcing the Pennsylvania Game Commission to reduce or cancel the next antlerless seasons. Groups of furious hunters this year have sought legislative intervention and threatened a hunting boycott if the commission doesn't scale back its allocation of antlerless tags.
Most states experienced similar turmoil long ago and moved on. Pennsylvania is "where we were in the '60s," observed Larry Herrighty, chief of wildlife management in Trenton.
Even without conflicting beliefs, managing deer is a complex assignment in the real world, where each acre differs.
Perhaps the biggest challenge is determining how many animals any given piece of habitat can support. The number can change significantly over time.
For instance, forests pass through known life stages, said Diefenbach, the research unit biologist. Younger forests, with higher proportions of seedlings and saplings that grew from clear-cut lands in the early to mid-1900s, can support up to 60 or so deer per square mile without damaging the habitat.
In middle-age forests, closely packed trees known as pole timber allow little light to reach the ground, limiting nutrients for deer; more than five per square mile may be too many. The oldest stage, saw timber, thins as trees die, allowing roughly 20 whitetails per square mile.
In decades past, hunters built camps in young forests "that provided lots of food for deer," Diefenbach said. "In the past 30 years, we're seeing shifts."
A lack of food can mean unhealthy deer and unhealthy forest. The deer eat everything they can to survive, including saplings and seedlings needed for the next generation of trees. Scientists report a cascade of changes that can reduce populations of blue jays, wild turkeys and white-footed mice (they compete with deer for nuts) and may increase gypsy moths (which are killed by mice).
On the other hand, a lack of whitetails means unhappy sportsmen, whose adrenaline kicks in with every sighting.
"Any deer reduction, whether it's by plan or by nature, gets a negative reaction," said Keith McCaffery, a retired deer research biologist in Wisconsin. So asking hunters to help solve the problem - on a college-entrance exam or in the real world - can be asking for trouble.
In the 1940s, McCaffery recalled, when Wisconsin's herd mushroomed, revered conservationist Aldo Leopold led the fight for an antlerless season.
"He almost lost his job."
Contact staff writer Don Sapatkin at 610-313-8246 or firstname.lastname@example.org.
About This Series
Deer can evoke strong urges - prey to be stalked, innocence to be saved, nuisance to be eradicated. This series looks at how people's responses affect the animals, their surroundings, and all our futures.
Next Saturday: In suburban Philadelphia and throughout New Jersey, deer present an entirely different challenge.
Last Saturday: New Americans nearly wiped out whitetail deer by 1900. Then a backlash set the stage for boom times.
The Pennsylvania Game Commission will vote April 26 on deer management.
For last week's story, scientific reports, policy papers, and related information, go to http://go.philly.com/deer.