Fuel treatments change forest structure and spatial patterns of fire severity, Arizona, U.S.A.

Abstract

Fuel reduction treatments are often designed to achieve multiple resource management objectives in addition to reducing potential fire hazard. In the White Mountains of Arizona State (U.S.A.), the 2014 San Juan Fire burned through several thinning prescriptions designed to achieve wildlife habitat objectives. Many studies have documented reduced fire severity for a standard set of fuel treatments, but the range of variability in fuel treatment effectiveness for alternative treatment designs is poorly understood. We used nonlinear mixed-effects modeling to estimate the distance into the treated area at which fire severity decreases and randomization tests to compare forest structure. High-severity fire effects were estimated to be reduced between 114 m and 345 m into the treated area. The range of variability in observed-distance high-severity fire effects persist into the treated area and, in conjunction with estimated relationships between posttreatment forest structure and severity, can inform the design of alternative fuel treatment prescriptions with various target prescriptions. We found that as cover was maintained in a treatment unit for wildlife habitat, the size of the fuel treatment necessary to observe a reduction in severity needs to be larger. Our study will inform decision makers on the size of treatments required to accomplish management objectives.