Given regional increases in fire activity throughout western North American forests, understanding how fire influences the extent and effects of subsequent fires is particularly relevant. In areas where fire regimes and forest structure have been dramatically altered, there is increasing concern that contemporary fires have the potential to set forests on a positive feedback trajectory with successive reburns; one in which extensive stand-replacing fire could promote more stand-replacing fire. On the other hand, low severity fire effects, in which surface and ladder fuels are reduced and dominant trees survive, have been shown to contribute towards subsequent low severity effects when reburned. The impact of initial fire effects between minimal overstory tree mortality (<20%) and complete (or nearly) overstory tree mortality (>95%), i.e., moderate severity, on fire effects in reburns is unclear. In this work we investigated the vegetation/fuel development pathways following different severity levels of initial fire and ascertained the influence of these on subsequent fire. Specifically, we examined the influence of forest structure, tree species composition, and shrub cover measured following initial fire on the severity in subsequent large wildfire events.
Results/Conclusions
Shrub cover and dead tree biomass (both standing and on-the-ground) were identified as influential, both of which were positively related to reburn severity. Our findings emphasize that the wide range of fire effects in reburns, which are not only a product of initial fire severity, but the initial forest condition (prior to fire) as well.