Prescribed Burning: Do We Really Know What We’re Doing?

New research shows that prescribed burning may be used too widely. The theory is that by reducing the unnatural fuel buildup caused by decades of fire suppression, prescribed burning reduces the risk of catastrophic fires. But this theory doesn’t fit all ecosystems, and prescribed burning can sometimes cause more harm than good.

“Although prescription burning has proven to be a viable means of reducing fire hazard in some forest types, it is not appropriate for the boreal forests of Canada and the chaparral shrublands of southern California,” says Jon Keeley of the USGS in Sequoia-Kings Canyon National Park, Three Rivers, California. Keeley and other researchers explore fire management in five papers in the December 2001 issue of Conservation Biology.

The idea of using prescribed burns to reduce large, intense forest fires throughout the western U.S. came from studies of yellow pine forests in the interior West, such as northern Arizona. Historically, these yellow pine forests had frequent surface fires that resulted in an open-canopy mosaic of old and young stands of trees. Fire suppression led to an unnatural buildup of small trees and dead branches and needles on the forest floor, which then fueled catastrophic crown fires.

But although prescribed burning makes sense for these yellow pine forests, this management technique is not warranted everywhere in the West. Notably, prescribed burning fails to reduce crown fires in closed-canopy forests and shrublands, where large, intense fires are natural and burn through young and old stands alike, says Keeley. Moreover, prescribed burning can have adverse ecological consequences in closed-canopy forests and shrublands. For instance, when prescribed burns are more frequent than the natural fire regime, they can outstrip native species’ ability to recover and so lead to local extinctions.

One example of a closed-canopy forest where the “yellow pine” model has been misapplied is Canada’s boreal forest, which grows in high latitudes and typically has short trees. These forests have always had stand-replacing crown fires, and there is little evidence that fire suppression efforts have reduced the size or frequency of these fires, say E. A. Johnson of the University of Calgary in Canda and his two colleagues.

Another ecosystem where the “yellow pine” model has been misapplied is southern California’s chaparral, where prescribed burning has been widely used to create a mosaic of different-aged patches. The idea was that young patches have less fuel to support a fire, so they would help keep blazes from spreading. The problem with this idea is that southern California’s large fires are driven by high “Santa Ana” winds and are not stopped by young chaparral patches, says Keeley.

This view is supported by the fact that despite active fire suppression, the area that has burned in recent decades has remained constant or increased, say Keeley and C. J. Fotheringham of the University of California at Los Angeles. Another reason they oppose widespread prescribed burning in southern California chaparral is that it can have adverse ecological consequences. For instance, frequent fires can promote the invasion of non-native grasses.

While the authors of most of the fire management papers in the December issue of Conservation Biology agree with Keeley, one does not. Richard Minnich of the University of California, Riverside argues that today’s catastrophic fires in southern California chaparral are far from natural, and he favors the current regime of widespread prescribed burning. “From a management perspective, my model provides a mechanism that may reduce catastrophic fires. Their method offers no management alternative,” he says.

Keeley and Fotheringham counter that the answer is to reduce urban sprawl into wildlands, teach land planners that fire management cannot eliminate fire hazard, and teach homeowners how to reduce fire hazard.

Further Information:
Keeley, J.E. and C.J. Fotheringham. 2001. History and management of crown-fire ecosystems: A summary and response. Conservation Biology 15(6):1561-1567.

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