Improving restoration of mixed-severity fire regimes: Looking back to move ahead

Background/Question/Methods

Roughly 43% of area treated for forest restoration or fire mitigation under the National Fire Plan fall within mixed-severity fire regime types.  One of the central questions that must be answered to understand the efficacy of current forest restoration policies in mixed-severity forests is the probability that a treated stand will experience wildfire during the “relevant” treatment lifespan.  Policymakers and managers are assigning substantial ecological and economic benefits to forest restoration treatments, such as deterring adverse ecological impacts of severe wildfire and reducing costs of wildfire suppression and post-fire rehabilitation.  These benefits are based on the assumption that treated stands will burn within the treatment lifetime; however, there has been little analysis of the extent to which previous restoration treatments within mixed severity forests have burned, the probability that they will burn, or the temporal duration of treatment benefits.  We assessed the percentage of mixed-severity regime forest area treated under the National Fire Plan that was located near (within 1.5-km of) a subsequent wildfire, compared treated areas to wildfire probability models for the western US, and assessed treatment lifespan by testing for relationships between year treated and fire severity (dNBR) for the subset of treatments that experienced subsequent wildfire.

Results/Conclusions

Findings suggest that only a very small percentage (< 10%) of forests within mixed-severity fire regimes that have been treated for restoration will experience wildfire in the short-term (4-yrs after treatment).  Similarly, area treated had on average relatively low burn probabilities (under 0.3).  Burn probabilities of treated stands were roughly equivalent to those of forests across the West, suggesting a need for more strategic placement of treatments intended to mitigate the effects of severe wildfire.  Overall, findings suggest that treatments may not contribute to reducing the ecological and economic costs of wildfire; thus there is the need for expanding the objectives of restoration treatments in mixed severity forests to improve ecological outcomes in the absence of subsequent wildfire.