Background: Maximizing the effectiveness of fuel treatments at landscape scales is a key research and management need given the inability to treat all areas at risk from wildfire. We synthesized information from case studies that documented the influence of fuel treatments on wildfire events. We used a systematic review to identify relevant case studies and extracted information through a series of targeted questions to summarize experiential knowledge of landscape fuel treatment effectiveness. Within a larger literature search, we identified 18 case study reports that included (1) manager assessment of fuel treatment effectiveness during specific wildfire events; (2) fuel treatment effects on fire size, severity, and behavior outside of the treatment boundaries; and (3) the influence of fuel treatments on fire suppression tactics. Results: Seventeen of the 18 case studies occurred in the western United States, and all were primarily focused on forested ecosystems. Surface fire behavior was more commonly observed in areas treated for fuel reduction than in untreated areas, which managers described as evidence of treatment effectiveness. Reduced fire intensity diminished fire effects and supported fire suppression efforts, while offering the potential to use wildfires as a fuel treatment surrogate. Conclusions: Managers considered treatments to be most effective at landscape scales when fuels were reduced in multiple fuel layers (crown, ladder, and surface fuels), across larger portions of the landscape. Treatment effectiveness was improved by strategic placement of treatments adjacent to prior treatments or past wildfires, in alignment with prevailing winds, and adjacent to natural fire breaks (e.g., ridgetops), efforts that effectively expanded the treatment area. Placement in relation to suppression needs to protect infrastructure also can take advantage of continuity with unvegetated land cover (e.g., parking lots, streets). Older treatments were considered less effective due to the regrowth of surface fuels. Treatment effectiveness was limited during periods of extreme fire weather, underscoring the need for treatment designs to incorporate the increasing occurrence of extreme burning conditions. Overall, fuel treatment effectiveness would be improved by the increased use of landscape-scale treatment designs that integrate fuels, topography, prevailing winds, fire or treatment history, and available infrastructure.
