COS 99-5
Spatial patterns of fire severity and vegetation structure in multiple wildland fuel treatments surrounding the WUI in the 2011 Wallow Fire

Thursday, August 14, 2014: 9:20 AM
Regency Blrm F, Hyatt Regency Hotel
Maureen C. Kennedy, School of Environmental and Forest Sciences, University of Washington, Seattle, WA
Morris C. Johnson, Pacific Wildland Fire Science Laboratory, Pacific Northwest Research Station, Seattle, WA

Fuel reduction treatments are designed to reduce fire hazard, yet fuel reduction projects are often subjected to many competing interests such as wildlife habitat concerns, restoration of historical stand structures and fire regimes, and the aesthetic quality of the forest surrounding residential communities (the wildland-urban interface; WUI). Treatment prescriptions that consider balancing these often competing criteria may modify the efficacy of the fuel treatment prescriptions in reducing fire hazard, which is of particular concern in the WUI.  In the year 2011 the Wallow Fire in Arizona (USA) burned through recently implemented fuel treatments surrounding the WUI. Multiple fuel treatment prescriptions had been implemented, providing an opportunity to compare the efficacy of the prescriptions in reducing fire severity. One treatment allowed for clumps of trees and buffers for wildlife habitat in the treated area, balancing the concerns of the community with the overriding goal of reducing fire hazard. Another prescription resulted in evenly distributed trees with complete removal of ladder fuels, emphasizing hazard reduction above other criteria. We measured fire severity and vegetation structure after the fire in these two kinds of treatments.  


Non-linear models fit to fire severity (crown scorch and bole char) showed that high severity fire was maintained a greater distance into the fuel treatment that retained clumps of trees than the treatment in which ladder fuels were removed. Maximum values of crown scorch persisted further into the treated areas than did maximum values of bole char for all treatments, which implies that a high intensity surface fire was maintained in the treated areas. All of the fuel treatments had reduced severity relative to the neighboring untreated forest. Post-fire reconstructed values of canopy bulk density, tree density, basal area and stand density index show those values to be lower in the treated area than the neighboring untreated forest, which is consistent with lower fire hazard in the treated area. Canopy base height was higher in the treated area than in the neighboring untreated forest, which is also consistent with reduced fire behavior. Despite the differences in treatment prescription, all of the fuel treatments we studied demonstrated modified vegetation structure and reduced fire severity, which allowed for safe opportunity for the protection of homes during the wildfire. This demonstrates that multiple criteria can be balanced in designing fuel treatments in the wildland surrounding the WUI.