USA –– MISSOULA, Mont. — On a forested mountainside charred in a wildfire in 2003, Richard Hutto, a University of Montana ornithologist, plays a recording of a black-backed woodpecker drumming on a tree.
The distinctive tattoo goes unanswered until Mr. Hutto is ready to leave. Then, at the top of a tree burned to charcoal, a woodpecker with black feathers, a white breast and a yellow slash on its crown hammers a rhythmic response.
“This forest may have burned,” says Mr. Hutto, smiling, “but that doesn’t mean it’s dead. There’s a lot going on.”
The black-backed woodpecker’s drum signals more than the return of life to the forest. It also may be an important clue toward resolving a debate about how much, and even whether, to try to prevent large forest fires.
Scientists are at loggerheads over whether there is an ecological advantage to thinning forests and using prescribed fire to reduce fuel for subsequent fires — or whether those methods actually diminish ecological processes and biodiversity.
The U.S. Forest Service, which manages nearly 200 million acres of public land, believes limited thinning and burning will prevent catastrophic wildfires. The agency contracts with logging companies to cut down large and small trees across sweeping landscapes, and uses prescribed fire. Besides protecting homes, experts say, these methods also re-create the natural state of the forest.
The approach, developed primarily as a result of tree ring studies, seeks to reconstruct the forests of the West before the 20th century, when the large-scale suppression of wildfire first occurred.
Some ecologists and environmentalists, however, are challenging the Forest Service’s model, saying it is based on incomplete science and is causing ecological damage.
Recent research, they say, shows that nature often caused far more severe fires than tree ring records show. That means the ecology of Western forests depends on fires of varying degrees of severity, including what we think of as catastrophic fires, not just the kinds of low-intensity blazes that current Forest Service policy favors.
They say that large fires, far from destroying forests, can be a shot of adrenaline that stimulates biodiversity.
The black-backed woodpecker could be an important indicator of which side is correct.
The bird lives almost exclusively in severely burned forests. It thrives on the fire-chaser beetle and the jewel beetle, which are adapted to fires and can detect heat 30 miles away with infrared sensors under their legs. Both species lay eggs only in scorched trees whose defenses have been wiped out by fire.
The black-backed woodpeckers feast on the beetles’ grubs. Their coloring has evolved to blend in with charred trees so they are not visible to hawks and other predators as they peck away.
Tracking the presence of the woodpeckers can indicate whether there are enough severe fires to stimulate their ecosystems and keep their numbers, as well as those of other species, healthy.
William Baker, a fire and landscape ecologist at the University of Wyoming, contends that the kind of limited fires that are being employed to control bigger fires were not as common in nature as has been thought.
For a recent paper in the journal Global Ecology and Biogeography, published with Mark Williams, Mr. Baker employed an unorthodox method to reconstruct fire history that challenges current analysis of tree rings. (The study was financed by the National Science Foundation andthe U.S. Agriculture Department.)
Mr. Baker and Mr. Williams examined thousands of handwritten records created by federal General Land Office agents who surveyed undeveloped land in the West in the mid-19th century. The surveyors used an ax to mark trees at precise intervals and took meticulous notes on what the vegetation between marked trees looked like — meadow, burned forest or mature trees.
Altogether, Mr. Baker’s students combed through 13,000 handwritten records on 28,000 marked trees and hiked miles in Oregon, Colorado and Arizona to find some of the trees and compare today’s conditions with those from the 1800s.
They found that low-intensity fires that occurred naturally were not as widespread as other research holds and that they did not prevent more severe fires. Mr. Baker concluded that big fires are inevitable and argues that it is best for ecosystems — and less expensive — to put up with them.
“Our research shows that reducing fuels isn’t going to reduce severity much,” he said. “Even if you reduce fuels, you are still going to have severe fires” because of extreme weather.
Jennifer Marlon, a paleoecologist at Yale University who has studied 3,000 years of fire history in the West, said her work led to a similar conclusion. Compared with the past several thousand years, she said, “fires in the West the last hundred years have been unusually low.”
But other fire researchers say they are not yet ready to abandon the current model.
“It’s interesting data and needs to be tested,” said Peter M. Brown, a dendrochronologist in Fort Collins, Colo., who studies fire history and consults with the Forest Service. But it’s not nearly enough, he said, to change the current model.
Some see support for the argument against prescribed burning in the fading populations of black-backed woodpeckers in California, Oregon and South Dakota. This year four environmental groups filed a petition to have the bird declared endangered, blaming the Forest Service’s policy for the decline.
Proponents of the free-fire theory say that while human lives and property should be protected, beyond that widespread wildfires should be viewed as necessary ecological events that reset the clock on a landscape to provide habitats for numerous species for years and even decades to come. This principle stems from research into “disturbance ecology.” For instance, when a hurricane blows down a large swath of forest or a volcano erupts, it strongly stimulates an ecosystem, scientists have found.
“Disturbances are very important; they are huge,” said Mark Swanson, a Washington State University ecologist who recently published a paper noting that recovered areas thrived after the eruption of Mount St. Helens in 1980. “You actually have an increase in species richness, sometimes to regionally high levels.”
Mr. Hutto, the University of Montana ornithologist, said he believes that the Forest Service approach is misguided. He pointed out that morel mushrooms thrive on charred ground, and that birds, including the mountain bluebird and black-backed woodpecker, then move in.
Similarly, a plant called snowbush can remain dormant in the soil for centuries until heat from a fire cracks its seed coat, and it blooms profusely.
“The first year after a fire is when the magic really happens,” Mr. Hutto said.