Large Santa Ana wildfires have been a regular occurrence along the southern California coast for more than 560 years, UC Berkeley study finds

By Robert Sanders, Public Affairs

BERKELEY--As California's fire season heats up, a team of California and Nevada geographers has sobering news for those living in fire-prone areas along the coast.

After digging up evidence that regular fires have devastated coastal areas for more than five hundred years, they caution that big wildfires pushed by Santa Ana winds and fueled by dry vegetation are likely to occur no matter how aggressive we are at fighting small blazes.

Reporting in the current issue of Quaternary Research (Vol. 51, p. 295-305), the scientists show that, for the past 560 years, big Santa Ana fires have occurred in the Santa Barbara area on average every 20 to 30 years, irrespective of what coastal residents were doing to suppress or prevent them.

The team consists of Scott A. Mensing, an assistant professor at the University of Nevada, Reno; Joel Michaelsen, a professor of geography at the University of California, Santa Barbara; and Roger Byrne, an associate professor of geography at the University of California, Berkeley. Both Mensing and Michaelsen began the research project while working on their doctorates in geography at UC Berkeley.

"Even with modern fire suppression, our ability to suppress very big fires in chaparral is extremely limited," Mensing said. "Given certain weather conditions - very dry weather and strong, Santa Ana winds - if the chaparral is ignited it can burn large areas in a very short time."

The scientists looked at the history of large fires in the coastal area around Santa Barbara, going back to the 15th century. In this century, fires burning more than 50,000 acres occurred in the Santa Barbara area in 1925, 1955, 1965 and 1985, despite active attempts since the turn of the century to suppress them.

"Some claim that fire prevention has created the problem by causing a buildup of fuel that allows catastrophic fires pushed by Santa Ana winds," Byrne said. "Our results show that's probably not a fair criticism. These fires will occur no matter what - they're just a natural part of the environment here."

The conclusion that such large wildfires are inevitable probably applies to other coastal areas of California with a similar Mediterranean climate and vegetation, Mensing said - basically the coast from Santa Barbara south to the Los Angeles basin. However, coastal conditions like these occur to some degree from San Francisco to San Diego.

"Based on what we've seen, any time you get dense chaparral, dry conditions and high winds, we can't control the fires that break out," Mensing said, pointing to the 1991 fire in the Oakland and Berkeley hills that burned 3,000 homes and killed more than two dozen people.

Chaparral is a term for brushy, treeless areas, comprised in the Santa Barbara area mostly of chamise, manzanita and ceanothus - all plants that have adapted to periodic fires.

"Nobody wants to hear it, but the solution is to control growth in high fire-risk areas by rezoning to limit construction," Mensing said. "Keep homes out of there."

The historical data on big fires in the Santa Barbara area came from a unique record - seasonally layered sediments in an undisturbed undersea basin in the Santa Barbara Channel, between the mainland and the Channel Islands. Like tree rings, the yearly layers in the sediment cores obtained from this basin provided a high resolution record of environmental change, Byrne said.

Researchers at Scripps Institution of Oceanography dated the cores by carefully counting the individual layers and by cross correlation with tree ring records from nearby areas.

Mensing and Byrne analyzed microscopically small particles of charcoal in the cores. High concentrations of charcoal indicate a large near-shore fire with a smoke plume pushed offshore, presumably by strong Santa Ana winds. Some of the charcoal fragments show a distinctive cell structure identified as coming from grass or wood.

Based on the chronology of the core, the team assigned specific years to samples covering the period AD 1425 to 1985. The charcoal evidence shows that during this period there were 20 "large" fires - fires that burned more than 50,000 acres. The cores do not record evidence of fires beyond about 50 kilometers away, Byrne noted. For example, a large fire in 1966 that burned to the north of Santa Barbara did not produce a significant increase in charcoal in the core.

The time between large fires - 20 to 30 years - was about the same no matter who was living on the coast: the Chumash Indians, who dominated the area until about 1770 and, based on historical records, apparently burned the area frequently; the Spanish and early Americans (1770-1900), who outlawed fires in the area to prevent wildfires; or recent generations (1900-1985), who have emphasized quick-response fire suppression.

Michaelsen correlated the charcoal record with tree rings to determine whether or not there was a climate connection. He found that big fires typically occurred after a long period of wet winters, at the beginning of a drought.

The findings dovetail with a report two months ago in the journal Science. That study concluded that fires in chaparral are difficult to put out no matter how old or recently burned the brush. This implies that prescribed burns - small, controlled fires set to limit the buildup of highly flammable fuel - don't work. The chaparral eventually will go up in flames anyway, Mensing said.

"Based on our channel record, it appears that very large fires are a natural part of this environment," he said. "They're not just a reflection of fire suppression, but of the flammable chaparral, and the Santa Ana weather condition that periodically develops along the coast."

Byrne previously had analyzed another core from the Santa Barbara basin - one that spanned the years 730 to 1505 AD - and found similar evidence of large fires. The current study confirms this earlier work and for the first time provides a complete record that spans the Chumash, Spanish and American periods of settlement.

The work was funded by the National Science Foundation and the California State Integrated Hardwood Range Management Program.

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