How a Forest Stopped a Fire in Its Tracks

July 22, 2003


SUSANVILLE, Calif. – Where the fire came through Blacks Mountain ExperimentalForest last September, the ground is

ash and the trees are charcoal. Black and gray are the colors, lightened onlyby small mounds of red dust at the base of some of the charred trunks – theleavings of bark beetles – and flecks of green where new growth pokes above

the ash. Through the tall, ravaged columns, however, a living pine forest isvisible. And as visitors inspecting the fire

damage walk toward the living forest, they come to an abrupt transition.September’s blaze was named the Cone Fire, for the hill where it was firstthought to have begun. It burned 2,000 acres of Lassen National Forest, and1,600 of those were in Blacks Mountain Experimental Forest, a 10,000-acre areawithin Lassen set up in 1934 for ecological study by the Forest Service.

When the Cone Fire swept through these woods it came to a patch of forestthat was different from the rest, and stopped dead, like a mime at an invisiblewall. What stopped the fire was an experimental plot that had been selectivelylogged to thin it, and had been burned in controlled fashion. The result was anopen forest, much the way it might have been 500 years ago when regular forestfires swept through the high dry country and no one tried to stop them. “Itjust stopped,” Carl N. Skinner said, looking satisfied but almostsurprised. Mr. Skinner, a geographer with the Forest Service at the ReddingSilviculture Laboratory in Redding, Calif., and Dr. Steve Zack, a conservationscientist with the North American Program of the Wildlife Conservation Society,along with other Forest Service colleagues, are showing a reporter the resultsof an accidental experiment that still impresses them each time they visit it.

“Night and day,” Dr. Zack said. “If we hadn’t treated this itwould have just blown right through this area,” Mr. Skinner said. Themembers of the group are part of a cooperative research project involvingdifferent parts of the Forest Service and the Wildlife Conservation Society. Theresearchers have been trying different forest management plans on 12 250-acreresearch plots for about seven years. The point was never to find out how bestto stop fires. Instead the research was meant to develop a general picture ofhow different management techniques affect forest ecosystems. In the past, manyforests were either cut down for timber or left alone. A century of firesuppression resulted in the accumulated underbrush and thick tree growth thatcan fuel catastrophic wildfires. Parts of Blacks Mountain and the surroundingLassen National Forest have had enough time to grow thick and brushy.

In the experimental plots, some were selectively logged, either to removebigger trees, to mimic one lucrative logging approach, or to leave a wide rangeof tree sizes. The plots that had the large trees removed were so-called lowdiversity plots.

“So much of this kind of forest has had the large trees removed over theyears,” Mr. Skinner said, and now “we have very dense forests thatneed thinning now from a fire hazard perspective. This is what many of them aregoing to end up looking like.”

Other plots were both thinned and subjected to prescribed burns – fires setby the researchers, a management policy that is followed in many nationalforests. Finally, some areas were subjected to prescribed burns only. Theresearchers – fire ecologists, wildlife specialists, botanists – have followedthe changes in plant growth, tree growth and wildlife populations in all thedifferent situations.

Ponderosa pine forests are no strangers to fire. Mr. Skinner has takensamples of trees up to 700 years old to find out their fire history. Most treesshowed evidence of some sort of fire about every 7 to 10 years. And big, intensefires occurred every 20 years or so, up until a century ago when the idea offighting forest fires took hold.

Once the natural fires were stopped, Dr. Zack said, the Ponderosa and Jeffreypine forests from Baja California to British Columbia grew thick. Underbrush,fallen limbs and dry needles accumulated to make fuel to feed fires that wouldconsume the large trees and destroy whole stands of timber.

When the Cone Fire hit, it created a controlled experiment on how differentmanagement techniques, at least in this area, affected a big forest fire.

The results are clear to the naked eye. The fire started in an area where thewoods were thick, and quickly became intense enough to consume the woods that itwent through.  It was blown south and west, but it was turned away first bya mechanically thinned plot, which it scorched before dying out, and then by aplot that had been subjected to thinning and prescribed burning. The fire didnot penetrate that patch at all. In the thinned area that had no controlledburn, Mr. Skinner pointed to the effects of the Cone Fire. “We definitelychanged the fire behavior and made it so the fire dropped to the ground and madeit so that from a point of view of putting out fires it’s easier to putout,” he said, “but still there’s sufficient fuel here to cause a lotmore damage to the stand that was left here.” Doing controlled burns, withno thinning, worked better. But the best of all was a combination of thinningand controlled burns. The stands of moderate-size trees, what the researcherscall “low diversity,” stopped the fire cold. The high diversitystands, which included more large trees, showed some scorching for 30 yards orso, as the fire burned the needle bed that had accumulated over five years sincethe last controlled burn. Then the fire died out. Dr. Scott Stephens, directorof the Stephens Laboratory for Wildland Fire Science at the University ofCalifornia at Berkeley, has been to Blacks Mountain Forest and seen whathappened when the Cone Fire hit. He said in an interview that this kind ofaccidental research with rigorous data was very rare.

He would have predicted, he said, that thinning and burning together wouldstop a fire, but was surprised that the plots that were thinned but not burnedsurvived as well as they did. Many trees died, but enough lived for the stand torecover.

The key, he said, was that when the small trees were cut, they werecompletely removed, rather than leaving remnants on the forest floor, as wasdone with the larger trees. That reduced the fuel on the ground. “It reallypoints to surface fuel reduction,” he said, as the most important step toprevent big fires. Dr. Stephens said the Bush administration’s current HealthyForest Initiative was mainly about reducing regulation and does not specify firemanagement regimens. He also said he thought that not enough emphasis in theinitiative was placed on reducing surface fuels by prescribed burning or othermeans. Whether large trees were removed or left made a big difference forwildlife, Dr. Zack said. Large trees, and large dead trees, are attractive towoodpeckers and other creatures. Although prescribed burns are common, they arealso controversial, partly because of a fire in New Mexico in 2000 thatdestroyed 200 buildings in Los Alamos, leaving hundreds of people homeless. Thatfire resulted from a prescribed burn by the National Park Service that got outof control.

Cost is also an issue. In plots where large trees were removed, timber saleswere lucrative enough that the net gain was $1,400 an acre. Where only smallertrees were cut, the Forest Service suffered a net loss of $200 an acre. Dr. Zackand Mr. Skinner and their colleagues agree that no single panacea will solve theproblems resulting from a century of fire suppression. Still, they can point tothe evidence on the ground, where you can stand on a line between charred treesand healthy ones.


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