Still baffled by mountain chaparral that is withering and dying on local hillsides, fire officials said this week that they plan to step up creation of firebreaks around the San Fernando Valley this spring to protect residential neighborhoods.
Los Angeles County Fire Department officials said their first priority will be to set a series of small, controlled fires south of Woodland Hills to create a 450-acre safety zone around the vulnerable northern edge of Topanga Canyon.
Similar burned-away firebreaks--dubbed "prescribed burns" by firefighters--are planned this year in Calabasas, Agoura Hills, Chatsworth, Simi Valley, Newhall and Valencia.
Increased use of such firebreaks was spelled out as a two-day symposium on urban-area brush control began in La Canada Flintridge. A Wednesday session drew more than 100 firemen, mountain parkland managers, flood-control experts and environmental scientists.
Fire officials said they can save money and satisfy environmentalists by putting the torch to hillsides under controlled conditions. Using bulldozers to clear an area is at least 10 times more expensive and causes erosion later, they said.
Researchers said a series of high-altitude reconnaissance flights over local mountains has failed to pinpoint what is killing brush and leaving slopes laden with tons of highly flammable dead vegetation.
The dying chaparral has been reported in the San Gabriel and Santa Monica mountains and in the Santa Barbara area.
U.S. Forest Service researcher Phillip Riggan said, "We're still trying to find out what the problem is. We think drought stress is the key to the condition."
He said he was referring to unusually heavy rain a few winters ago that may have caused the brush to grow faster than normal, leaving the vegetation weakened when rainfall became lighter. Air pollution and an "acid fog" condition near Los Angeles also could have contributed to the problem, he said.
Riggan said the latest estimates are that as much as 60% of the ceanothus shrubs on about 200,000 acres of wild land in Southern California will succumb.
At residential areas that are surrounded by brush, "you're going to be looking at a spectacular fire," he said.
Benefits of Breaks Shown
Although computer-enhanced, infrared pictures--snapped from a modified U-2-type spy plane owned by the National Aeronautics and Space Administration--did not unravel the shrub mystery, they offered new proof of the benefits of pre-burned firebreaks, he said.
Aerial photos taken after July's brush fire in the Lake Sherwood area south of Westlake Village showed that the fire halted in an area blackened by an earlier brush fire, he said.
County Fire Department Capt. Scott Franklin said nearly 12,000 acres in mountainous areas around the San Fernando Valley have been earmarked for firebreak-burning this spring.
Firefighters will set the small fires on windless days when humidity measurements show that brush will burn slowly, he said. That way, firefighters can control flames to burn large clumps of brush but preserve some smaller live shrubs needed for erosion control. Environmentalists generally support the burning exercises because such low-intensity fires aid in the regeneration of native seeds.
Last year's firebreak effort was cut short by hot, dry weather, when it was feared the fires could not be controlled.
Franklin said the crest of Topanga Canyon, between Mulholland Drive and Santa Maria Road, is his department's top priority for firebreaks because "Topanga Canyon has a tremendous fire threat.
"We want to start breaking that up. We get a fire coming in from Woodland Hills and we're talking about losing hundreds of homes in Topanga," he said.