Fire Confirms Fears About Brush Dieback

The widespread death of mountain shrubbery, which has worried Southern California firefighters for months, caused the Lake Sherwood brush fire to burn faster and hotter than it would have otherwise, a Los Angeles County Fire Department official said.

Preliminary examinations indicate that the dieback problem may change mountain ecology seriously enough to aggravate brush-fire problems for years, Capt. Scott Franklin warned.

He said it was clearly evident that the fire burned hotter in the dieback areas--”hot enough to break rocks.” High heat worsens long-term soil damage, which increases erosion and changes vegetation patterns.

In a related action, U.S. Forest Service scientists who have been researching the dieback since it was noticed in the early spring, seized on the opportunity offered by widespread brush fires this week. They talked NASA into flying a hastily arranged high-altitude research mission over the fire zones Tuesday.

Lack of Rain

Researchers now suspect the dieback is related to a lack of rain this year, after several rainy winters that encouraged wild brush to grow beyond its ability to survive in such a dry year. Some researchers think air pollution may also be involved.

Franklin estimated that ground temperatures reached 1,200 degrees in the dead-brush zones of the Lake Sherwood fire, twice as high as the 600 degrees such a fire would normally generate.

At such high temperatures, he said, “the soil goes through physiological and chemical changes.”

One result is that the seeds and roots of wild shrubs, which adapted through evolution to lower-temperature wildfires, are harmed by such high heat. Another is that the top layer of soil is baked into a sheet of resin-coated particles “like tiny popcorn,” which easily washes away in the first rainfall, he said.

‘Starting to Erode Already’

“Some of it is starting to erode already, even without the rainfall,” Franklin said.

He said the area where the Lake Sherwood fire burned was one of those he surveyed earlier this year for dieback damage, “and the fire followed the dieback patterns exactly.” He said the fire left a mosaic pattern of charred but perhaps salvageable vegetation “where the dieback had not reached, and nothing but white ashes where the dieback was.”

The dieback has claimed several species of mountain shrubs, but firefighters were most concerned about the loss of wild lilac. Because of their high moisture content, live wild lilac bushes resist burning, forming natural fire barriers. But the dieback converted the fire-resistant shrubbery into volatile dead wood, adding greater danger precisely where, in the past, firefighters counted on help from nature, Franklin said.

Trouble for Future

Franklin, who earlier estimated that the dieback had added as much as a million tons of highly flammable dead wood to the county’s mountain slopes, said he was worried “not just about this year, but because this fuel buildup will be with us for years to come . . . so we start experiencing fires earlier in the year” without waiting for the summer to dry out live vegetation.

“What we’re concerned about is a change in the ecosystem,” he said.

At some point, he said, fires that generate high heat could eliminate the natural growth “and replace it with a lower order of vegetation, sagebrush or grass, or things like that, which are more volatile on a short-term basis.”

He said that, “instead of having a high-intensity fire every 12 to 20 years” in the natural shrubs, “we could wind up with things that fuel a high-intensity fire every five years.”

An area of Chatsworth where there was such a change after a series of high-temperature fires in 1957 and 1958, “is just now starting to come back,” he said.

Determining the heat generated by this week’s fires, and the ground heat they built up, was the most important part of the NASA flight, said Philip Riggan, a U.S. Forest Service scientist.

Riggan is part of a team formed by the U.S. Forest Service, the California Department of Forestry and the Los Angeles County Fire Department to determine the extent, cause and effects of the dieback.

He asked NASA’s Ames Research Center near Sunnyvale for the mission Tuesday, he said, and within hours it was added to a previously planned flight, unrelated to the fires, over the Southern California area.

The flight was carried out by a NASA ER-2, an updated version of the U-2 spy plane with earth resources instruments, including infrared sensors that detect heat from great distances. The plane, which flies at about 60,000 feet, operates from the NASA office at Moffet Field, near San Jose.

Comparing Information

The data gathered by the flight will be compared with information from a similar flight June 11 over the dieback areas in the Santa Monica and San Gabriel mountains, Riggan said. The flight Tuesday also covered the Santa Ana mountains in Orange County “because the dieback is spreading down there,” he said.

The flight covered five fires in Southern California, he said, providing material that will take months to analyze. “We were pleased to get the images,” he said, “especially those of the Ojai fire, which was burning very vigorously when the pilot went over.”

The dieback increases the heat of a fire in part, Riggan said, because the dead wood includes large branches, which might resist burning if the shrub were alive and filled with moisture. “It’s like the difference between burning kindling in your fireplace and getting a big log burning. The big fuel releases more energy, more heat,” he said.