Previous fires moderate burn severity of subsequent wildland fires in two large western US wilderness areas
The authors examined fire-on-fire interactions in two wilderness areas to determine the extent to which a wildfire can influence the severity of a subsequent fire and, if so, how long does the effect last. They also looked at the influence of topography and vegetation on burn severity of reburned areas.
The authors found a positive feedback between the initial severity of a fire and the severity of a later reburn when the first fire burned at high severity. They suggest that high severity fires can leave behind dense stands of fire-killed trees, potentially creating heavy fuel loads and ladder fuels when a subsequent fire strikes. Alternatively, a shift to a shrub state after high severity fire can result in a subsequent reburn of high severity fire. However, they also found that stands that are within unaltered, short-interval fire regimes tend to self-regulate the burn severity of secondary fires, and burn at the same or lower severity, suggesting that the initial fire moderated the burn severity of the second fire. This mitigating effect lasted up to 22 years in some of the burned areas studied, but generally decayed as time since fire increased.