Previous Fires Moderate Burn Severity of Subsequent Wildland Fires in Two Large Western US Wildnerness Areas

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Fire exclusion has reduced frequency of fire and areas burned in many dry forest types, which may affect vegetation structure and composition, and potential fire behavior. Recent research suggests that landscapes with unaltered fire regimes are more "self-regulating" than those that have experienced fire-regime shifts; in self-regulating systems, fire size and severity are moderated by the effect of previous fire. To determine if burn severity is moderated in areas that recently burned, researchers analyzed 117 wildland fires in 2 wilderness areas in the Western US that have experienced substantial recent fire activity. Results show burn severity is significantly lower in areas that have recently burned compared to areas that have not. Results further indicate that burn severity generally increases with time since and severity of previous fires. These findings may assist land managers to anticipate the consequences of allowing fire to burn and provide rational for using wildfire as a "fuel treatment".