How big is enough? Vegetation structure impacts effective fuel treatment width and forest resiliency

Fuel treatments are designed with multiple management goals, including improving suppression capacity and restoring the historical structure of dry forests. Fuelbreaks are a class of fuel treatment that remove fuels within a wide strip of land, with an overarching objective to reduce fire behavior and provide safe access for suppression. In an empirical analysis of shaded fuelbreaks that burned during the 2014 Bald Fire (15,950 ha on the Lassen National Forest, California, USA), we found that overall fire severity was reduced in the treated areas relative to untreated. A non‐linear mixed effects model estimates that the reduction was detected more than 400 m into the treated area, greater than the standard width of the prescribed fuelbreak. Both pre‐ and post‐fire species composition differed between treated and untreated forest, with few living stems remaining in the measured untreated areas. In the post‐fire treated area, we documented a mixed conifer forest dominated by larger diameter Pinus, implying that the fuelbreak did result in a more resilient post‐fire structure and composition. These results indicate that fuelbreak design may need to be wider than generally prescribed and that even during extreme fire conditions fuel treatments can result in resilient forest structures.