Prescribed burns have been a favoured method of forest management and fire control for many years. 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 recent research suggests that 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," says Jon Keeley of the USGS in California's Sequoia-Kings Canyon National Parks, "it is not appropriate for the boreal forests of Canada and the chaparral shrublands of southern California."
Prescribed burns fail 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.
Keeley's criticism of overuse of prescribed burns has found some support north of the Canada / U.S. border. Canada's extensive boreal forests are one example of a closed-canopy forest. E.A. Johnson of the University of Calgary says boreal forests have relatively short trees. He says that 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 forest fires in these areas.