After blazes comes battle with erosion

Recovery: As nature heals itself in Southern California, experts plot ways to keep winter rains from washing away the exposed earth.

November 10, 2003|By Heather Dewar | Heather Dewar,SUN STAFF

Just days after rain quenched Southern California's wildfires, nature's disaster-recovery effort is already under way.

Deer are browsing in the burned-over zones where new growth has begun to appear. Long-buried seeds are preparing to sprout, in response to chemical signals in the wildfires' smoke. The same chemical cues draw insects to feast on dead wood - and the bugs in turn will draw songbirds in spring.

If nature had a free hand, fire would help keep the forests and scrublands healthy. And it would hasten the crumbling of young, unstable mountain ranges that, at 2 million to 5 million years old, are among the most rugged in North America, compared with the eroded 250 million-year-old Appalachians.

But more than 18 million people live in Southern California's valleys, canyons and mountains, and they want to tame the natural forces of fire and flood.

Twelve years after a disastrous Oakland Hills wildfire killed 25 people and destroyed more than 3,000 homes, Californians have learned that they might be able to control - if not prevent - wildfires in densely settled areas on the outskirts of a major city by eliminating most vegetation around buildings and along roads.

That's impossible in half-wild places like the San Bernardino Mountains, said Jon Keeley of the U.S. Geological Survey. There is no way to prevent fires in the chaparral that dominates all but the highest ground.

Scientists and land managers will allow nature to take its course on most of the 740,000 acres burned during October's firestorms. But experts are plotting a series of strategic battles against erosion.

When the region's autumn fires are followed by winter rains that course down steep, bare slopes, the result is a turbo-charged erosion cycle that has helped create what little flat terrain Southern California has, said Duke University ecology professor Norm Christensen, an expert on Western wildfires.

"Most of the sediment that makes up the Los Angeles Basin was probably deposited there as a result of fires," said Christensen, who led the federal government's scientific assessment of the 1988 wildfires in Yellowstone National Park. "It is a natural process. On the other hand, there are 20 million people in harm's way, so it's hard to put a happy face on it."

Land managers can't stop the erosion, but they're trying to control it, steering mudslides and flash floods away from roads, bridges and subdivisions. Much of the work is carried out by strike forces called Burned Area Emergency Response teams.

The BAER squads use satellite photos, aerial surveys and computerized mapping techniques to quickly assess erosion threats.

"They target only places where a flood can end up right in a community or a reservoir," said U.S. Forest Service ecologist Jan Beyers.

Land managers used to try stopping erosion by scattering rye grass seeds by airplane immediately after a fire. But research has shown that the seeding of non-native plants does more harm than good, said Keeley.

Unlike the seeds of native plants, which germinate in the spring, the European grasses sprout in the fall, making it look as though the land is healing. But they can't tolerate the region's long, dry summers and quickly die off, providing new fuel for fires. The result, Keeley said, is a speeded-up fire cycle. Some of this year's fires were in chaparral that burned just two years ago.

"People think chaparral is adapted to fire, but it's not that simple," Keeley said. "It's adapted to fires that come between 20 years and 100 years apart."

Most chaparral plants don't start producing seeds until they're at least 10 years old. If fires come more often, introduced grasses replace the native shrubs - which has already happened in about one-quarter of the chaparral.

Many private landowners still use aerial seeding as a form of "litigation protection," though they know it won't stop mudslides and will increase the fire risk, Keeley said. But the technique has fallen out of favor on public land. Instead, the BAER teams are turning to experimental techniques, such as heli-mulching - using helicopters to scatter hay across the most flood-prone slopes.

The crews move fire-downed trees, creating sediment channels that funnel debris away from homes, bridges and roads. It's labor-intensive work, and it doesn't satisfy the public hunger for a quick flush of green in a stark landscape.

"There's public pressure to do more," said Beyers. "People want to see something happening in the area that's burned. They don't understand that it will regrow if you leave it alone."

About 80 percent to 90 percent of the October wildfires were in chaparral, which stands the best chance of recovery from the fire, Keeley said.

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