Last year's devastating fires ignited new research challenging the assumptions for managing arid, fire-prone regions.

Natural fires, such as those found in Southern California, appear to be driven more by weather conditions than by the age of the region's plant life, according to a paper published in the May issue of Frontiers in Ecology and the Environment.

Examining the fire history of Southern California coastal and foothill shrublands, the research team discovered that the majority of shrubland burning risk was fairly steady, at about 2.7% each year. Of the 10 SITES surveyed, only one showed a marked increase in fire hazard as the plants grew older.

“Our results contradict the widely held belief that large wildfires in California shrublands are the direct result of unnatural fuel accumulation due to fire suppression,” said Max Moritz, a wildland fire specialist at the University of California, Berkeley.

These findings are important for fire management because local U.S. Forest Service departments consider pre-fire fuel manipulations a primary mean of dealing with the fire hazard inherent in these shrublands, Moritz said.

Rotational prescription burning to maintain a landscape of different age classes is thought to inhibit large fire development. The Moritz study suggests this strategy will be ineffective.

His results suggest a serious need for a reevaluation of current fire management and policy, which currently is based largely on eliminating older stands of shrubland vegetation.

Moritz said prescription burning in crown-fire ecosystems also has limitations not experienced in forest ecosystems.

Earlier work has shown it can be ecologically harmful to native species to employ prescription burning in relatively young shrublands before a sufficient seed bank has accumulated to ensure successful regeneration.

In addition, prescription fires in older shrublands are limited to weather conditions that minimize the chances that the flames will escape containment (in winter and spring), but these conditions may also inhibit post-fire recovery of vegetation.

“Although prescription burning and other fuel manipulations should still be useful at strategic locations along the urban-wildland interface, we may need to accept large fires as natural and inevitable events on many shrubland landscapes,” Moritz said.

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