A systematic review of empirical evidence for landscape-level fuel treatment effectiveness

Background Adverse effects of wildfires can be mitigated within fuel treatments, but empirical evidence of their effectiveness across large areas is needed to guide design and implementation at the landscape level. We conducted a systematic literature review of empirically based studies that tested the influence of landscape-level fuel treatments on subsequent wildfires in North America over the past 30 years to evaluate how treatment type and configuration affect subsequent wildfire behavior or enable more effective wildfire response. Results We identified 2240 papers, but only 26 met our inclusion criteria. Wildfire sizes ranged from 96 to 186,874 ha and total treated area ranged from 8 to 53,423 ha. Total treated area within a wildfire perimeter was highly correlated with wildfire area (r = 0.89, n = 93 wildfires), and the average proportion of wildfire area that was treated was 22%. All studies demonstrated wildfire behavior changes within treatment boundaries (i.e., site-level effect), but only 12 studies provided evidence that treatments influence wildfires outside of treatment boundaries (i.e., landscape-level effect). These 12 landscape-level papers showed effects on fire severity, fire progression, and fire extent, but were dissimilar in design and analysis approaches, constraining the ability to generalize about the type and configuration of fuel treatments to maximize effectiveness. Conclusions It is clear that the state of knowledge based on empirical evidence is at its infancy. This is likely because of the vast challenges associated with designing and implementing sampling designs that account for combinations of spatial and temporal configurations prior to wildfire occurrence. We also suspect part of the reason empirical evidence is lacking is because the distinction between site-level and landscape-level effects is not well recognized in the literature. All papers used the term landscape, but rarely defined the landscape, and some specified identifying landscape-level effects that were truly site-level effects. Future research needs to develop innovative ways to interpret the role of fuel treatments at the landscape level to provide insight on strategic designs and approaches to maximize fuel treatment effectiveness.