Scientists compared the effectiveness of fire fuel reduction methods under the U.S. National Fire and Fire Surrogate Study. Four articles examine the effects of prescribed burns, mechanical treatment (usually thinning of the smallest trees) and a combination of both with control plots at 12 study sites in forests across the United States.
Many U.S. forests once experienced frequent natural fires that removed many of the low-lying plants, including downed woody plants, shrubs and grasses that fueled these burns. But human activities, such as livestock grazing, preferential logging of large trees and outright fire suppression or exclusion have led to changes in forest structure. Increases in tree density, smaller tree size and increased fuel load place as many as 10 million hectares of U.S. forest at high risk of hazardous fires, the authors write.
Under extreme weather conditions, the authors found that prescribed fire alone, a combination of prescribed fire and mechanical fuel removal, and fuel removal alone were all effective at reducing fire severity. More specifically, they report that to quickly restore forests with few, large-diameter trees, a combination of prescribed burns and mechanical fuel removal achieved the best results.
The authors note, however, that this combination treatment also favored nonnative species invasions at some sites. In addition, a combination of prescribed burns and mechanical thinning increased the incidence of tree death from bark beetles and wood borers. Still, the authors emphasize that a no-treatment option is not sustainable in these fire-prone environments. They recommend caution and case-by-case assessments of best management practices for different forest types.
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