Fuel treatment prescriptions alter spatial patterns of fire severity around the wildland-urban interface during the Wallow Fire, Arizona, USA

Fuel reduction treatments are implemented in the forest surrounding the wildland–urban interface (WUI) to provide defensible space and safe opportunity for the protection of homes during a wildfire. The 2011 Wallow Fire in Arizona USA burned through recently implemented fuel treatments in the wildland surrounding residential communities in the WUI, and those fuel treatments have been credited with providing firefighter opportunities to protect residences during the Wallow Fire and thereby preventing the loss of homes that otherwise would have been burned. To characterize the spatial pattern of fire severity (represented by crown scorch and bole char) as the fire entered the treated areas from the wildland we fit non-linear models to the relationship between each severity metric and distance from the treatment edge in the direction of fire spread. The non-linear curve we chose provides an estimate of the distance into the treated area at which the severity metric is substantially reduced. Fire severity as measured by crown scorch and bole char was reduced a greater distance into the fuel treatment that allowed for clumps of trees and buffers for wildlife habitat than for the fuel treatment that resulted in evenly distributed trees with complete removal of ladder fuels. Crown scorch persisted further into the treated areas than did bole char, which implies that a high intensity surface fire was maintained in the treated areas. All of the fuel treatments we studied in the Wallow Fire demonstrated reduced fire severity before encountering residences in the WUI, demonstrating that there are multiple paths to fuel treatment design around the WUI.