Advertisement
YOU ARE HERE: LAT HomeCollectionsFires

With care, the forest will live

September 29, 2009|Julie Cart

Brent Roath quickly recast the question. Yes, he agreed, the U.S. Forest Service scientists who have spent the last two weeks in the San Gabriel Mountains examining the effects of the Station fire are like forensic pathologists combing a crime scene.

Except in this case, the patient is still alive.

"We're more like doctors, and our patient is ill. We're trying to figure out how to make it better," said Roath, regional director of post-burn analysis and a 33-year Forest Service veteran.

Although the 45-member team's report will remain under wraps for some time, the preliminary findings are in: Don't pray for rain.

Using sophisticated burn maps generated by satellite imagery and factoring in the breathtaking steepness of the now-denuded hillsides, the scientists warn that even moderate winter rain could trigger landslides and catastrophic debris flows capable of inundating many of the San Gabriels' 37 foothill communities.

Beyond that, the scientists concluded that although 250 square miles of the Angeles National Forest burned, the trees and chaparral in the fire-adapted ecosystem will bounce back.

However, much of the wildlife that makes its home in the 655,000-acre forest was killed or dislocated. Biologists say they found an unusually high number of large animals caught by the fast-moving fire. Teams have come across carcasses of bears, mountain lions, bobcats, coyotes and gray foxes, apparently unable to find escape routes.

"Deer took a big hit," said Kevin Cooper, a wildlife biologist.

The BAER team (for Burned Area Emergency Response) worked 14-hour days to complete its work, retreating each night to laptops at the "BAER Den," a Residence Inn conference room in Burbank.

Specialists were on the ground in every part of the 160,000-acre burn area, measuring, photographing and testing. The team included soil scientists, hydrologists, archaeologists, botanists, wildlife experts and a hazardous materials crew. The fire peeled back a layer of cover to reveal unknown Native American oven sites, scores of illegal dumps and a stash of 50-gallon drums filled with an as-yet unidentified liquid.

One day last week, Roath steered a white Forest Service SUV up the Angeles Crest Highway, which was closed to the public but nonetheless busy. Crews used graders to clear boulders, semi-tractor-trailers hauled debris and workers with chain saws cut trees that threatened to fall across traffic lanes.

Overhead, helicopters carried water-dropping buckets or ferried dangling loads of replacement utility poles.

For the most part, the landscape was devoid of color. Gray-white ash has banked in places, like dandruff on the shoulders of the mountains. Roath, a soil scientist who began his Forest Service career on the Angeles, is still awed by the immense natural forces once marshaled to lift this mountain range that is still rising and settling.

He noted that debris cones -- accumulated rock and sand at the bottom of sharply defined ridges -- are sprouting up everywhere, as though the mountains are shedding dead skin.

The San Gabriel Mountains have the potential to unleash calamity under normal circumstances, without the overlay of fire to complicate things. They are mountains on the move; the rock is fractured and disintegrating.

Roath said that as BAER team members collected their data, they could hear the rattling sound of mountains falling.

"In some cases boulders are coming down from gravity alone. They don't need rain," Roath said.

Vegetation plays a critical role in shoring up hillsides. When rains come, the drops hit the plant canopy first, which slows the water and distributes it more evenly into the soil. Absent vegetation, rain pounds down and washes away topsoil, sand, small rocks and burned plant material.

Thus begins a process that scientists call "entraining" -- the terrible freight of broken mountainside that gathers energy as it roars inexorably downhill.

Storms cause sediment to back up in ravines already loaded with fire debris. The flow bulges and spreads, picking up larger stones, then boulders. It gains speed as it descends, blowing obstacles out of its way. That debris, too, joins the train. As highway culverts become full, the entire river of rock flows over the roadway, collapsing it.

The broken asphalt then becomes a passenger on the cascading wreckage.

Trees, automobiles and houses scarcely slow the torrent.

"Debris flows are a little hard to control," said Sue Cannon, a debris flow expert with the U.S. Geological Survey in Denver, adding that the San Gabriels present a "classic setting for major debris flow."

Along the upper Big Tujunga Road, fire appeared to have followed the drainage, burning trees that straddled the creek, leaving "a pretty well-toasted riparian area," said Jan Beyers, a Forest Service plant ecologist.

Advertisement
Los Angeles Times Articles
|
|
|