Wildfire Regime in the Boreal Forest and the Idea of Suppression and Fuel Buildup

The explanation often given for the large wildfires that have burned each year in North America in the last two decades is that fire suppression after the 1950s produced a buildup of fuel and changed the landscape-age mosaic (e.g., Gayton 1998; Smalley et al. 2000), creating conditions for catastrophic fires. This idea of “unnatural fuel buildup” ( Brown 1983) was originally developed for Pinus ponderosa ecosystems in the interior West of the United States, where a historical regime of frequent surface fires had maintained open-canopy conditions. With the arrival of European settlers, the frequency of surface fires decreased, changing both the accumulation and arrangement of fine fuel. Growth of an intermediateheight layer of vegetation and the increased bulk density of canopy fuel allowed surface fires to burn into the crown, thus creating a crown-fire regime (Fuli et al. 1997; Shinneman & Baker 1997). Unfortunately, this fuel-buildup idea has been uncritically and inappropriately applied to closed-canopy ecosystems that have always had crown-fire regimes. Keeley and Fotheringham (2001 [this issue]) explain in the lead article of this forum why this concept is not valid for the California shrublands, and they present evidence that the presuppression fire regime had been one of standreplacing crown fires. We show here that the idea of unnatural fuel buildup is also invalid for the boreal and subalpine forest, another closed-canopy ecosystem with a crown-fire regime ( Johnson 1992). Despite differences in climate and vegetation between chaparral and boreal forest, many of the basic arguments and explanations we present are similar to those of Keeley and Fotheringham. Fire Regime of the Boreal Forest

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