Mysterious Plant Blight Killing Off More Brush
The chapparal-covered hills of Southern California appear to be lush with greenery, nourished by unseasonal autumn rains.
That should be good news for firefighters and forest researchers worried by the mysterious “die-back†that has been killing brush on the mountainsides for the last three years.
Instead, it’s bad news.
Because the die-back was blamed, in part, on four years of drought, precipitation was expected to ease the problem. But researchers now believe the warm rains actually fueled the fungus that causes the plant blight, making the situation even worse. The die-back, which appeared to have peaked more than a year ago, has now shifted into second gear, ravaging what remains of brushy areas depleted by the first round.
Approaching 50%
“In some areas of the Santa Monica Mountains, the die-back is approaching 50% or more,†said Los Angeles County Fire Capt. Scott Franklin, coordinator of vegetation management.
“We don’t have a firm count, but a conservative estimate would be that it has already killed about 15% to 20%†of the brush in Southern California, he said.
“If these were trees instead of brush--things like redwoods that people get emotional about--the public would be going crazy,†remarked Philip J. Riggan, a U.S. Forest Service scientist, one of the leading researchers into the die-back phenomenon.
Indeed, Riggan says, there is concern that the problem may be spreading to ornamental trees and shrubs in the yards of foothill residents--and that it could endanger prized oak trees.
But the focus of the research now is how to stop the mysterious die-back from killing off thousands of acres of brush--greatly increasing the danger of brush fires.
The problem is that the dead, tinder-dry brush provides “tons of additional fuel per acre in a brush fire,†said Capt. Ron Mathis, superintendent of a county firefighters camp in La Canada Flintridge as he recently surveyed a hillside in the San Gabriel Mountains with Franklin and Riggan.
Burns Hotter, Faster
Dead brush burns more readily, as well as hotter and faster, than live brush. The swifter burning rate increases the danger that a blaze will flare into a populated area or that an eruption of flames will trap firefighters, injuring or killing them, said David R. Neff, regional resources program manager for the Department of Forestry.
Instruments placed in the path of fires in areas devastated by die-back showed that soil temperatures reached levels as high as 1,200 degrees, twice as hot as temperatures in burning areas with mostly live vegetation, Franklin said.
Higher temperatures do more damage to topsoil and chaparral seeds, worsening soil erosion and mud slide problems and making it more difficult for the burned-over area to recover.
Especially worrisome for firefighters is the loss of ceanothus , also called wild lilac, a widespread shrub that has been one of the chief victims of the die-back. Healthy wild lilac has a high moisture content and resists burning, forming a natural fire damper.
The die-back, first seen in the San Gabriel Mountains in 1984 and then in the Santa Monicas in 1985, is evident throughout Southern California, Neff said.
“Now we find it in Santa Barbara County--up around Lake Casitas is the northernmost reach--and south to Temecula in San Diego County and eastward into Riverside County,†Neff said.
In June, 1985, at the request of die-back researchers, the National Aeronautics and Space Administration flew an ER-2 reconnaissance plane--a civilian version of a U-2 spy aircraft--over Southern California at 60,000 feet, photographing the area with regular, infrared and heat-sensitive film in an attempt to map the extent of the blight.
Researchers say they still do not understand the origin of the die-back. It does not seem to have a single cause, but is the result of several interacting factors, perhaps including some that are not yet known, they say.
One of the factors appears to be the fungus-- botryosphaeria ribis --which was identified by state researchers in 1986 and has been found in wild lilac bushes in die-back areas.
But the fungus alone does not seem to cause the die-back, Riggan said. It appears to be common throughout the chaparral area, but otherwise healthy plants usually resist it, he said. One theory is that the heavy rains of 1982 and even heavier storms of 1983--the year the El Nino condition in the Pacific Ocean sent a series of destructive downpours through Southern California--encouraged the chaparral to grow larger, or faster, than normal.
“They just grew like crazy after those storms in ‘83,†Franklin said.
Larger Root Systems
But the overextended shrubs had trouble surviving in the drought that began in 1984 because the excessively large root systems could not find enough moisture in the soil.
The weakened shrubs were then finished off by the fungus, Riggan and others theorize.
Riggan also suspects air pollution is involved because shrubs in areas with high pollution levels are more susceptible to the blight, but he said he does not have enough data to prove the point.
If lack of water was the trigger for the epidemic, however, the recent rains should have fortified the chaparral, easing the problem.
“But when we checked, we found it was spreading again, faster than ever before, which seems to fly in the face of the drought idea,†Franklin said.
It seems clear by now that the rain has been causing the die-back to spread, Franklin and Riggan agreed. “The die-back is appearing in large areas that resisted it before,†Franklin said.
Why, they don’t know.
Franklin speculated that the rainfall was warmer than later winter rains, and that the warmth may cause the fungus to spread.
Historical Perspective
One of the most vexing questions for researchers is whether the blight is unprecedented or if it has happened before.
Neff said state researchers and consultants with more than 30 years of experience, “people who have spent all their lives observing the chaparral, have simply never seen anything like it.â€
Riggan said he has found nothing like it in scientific literature, noting “there are clues that maybe this has happened before, but the researchers didn’t recognize it.
“Years ago,†he said, “they used to believe that chaparral just had a short life span, which we know now isn’t necessarily true.â€
Researchers have no idea what to do to combat the blight, he said.
“This is a whole natural ecosystem. Unlike the forests up north, which have been cut over by loggers, sometimes many times, this system is the way nature made it.
“And it’s just vanishing before our eyes.â€
