Factors affecting fuel break effectiveness in the control of large fires on the Los Padres National Forest, California

As wildfires have increased in frequency and extent, so have the number of homes developed in the wildland–urban interface. In California, the predominant approach to mitigating fire risk is construction of fuel breaks, but there has been little empirical study of their role in controlling large fires. We constructed a spatial database of fuel breaks on the Los Padres National Forest in southern California to better understand characteristics of fuel breaks that affect the behaviour of large fires and to map where fires and fuel breaks most commonly intersect. We evaluated whether fires stopped or crossed over fuel breaks over a 28-year period and compared the outcomes with physical characteristics of the sites, weather and firefighting activities during the fire event. Many fuel breaks never intersected fires, but others intersected several, primarily in historically fire-prone areas. Fires stopped at fuel breaks 46% of the time, almost invariably owing to fire suppression activities. Firefighter access to treatments, smaller fires and longer fuel breaks were significant direct influences, and younger vegetation and fuel break maintenance indirectly improved the outcome by facilitating firefighter access. This study illustrates the importance of strategic location of fuel breaks because they have been most effective where they provided access for firefighting activities.

Spatial Relationship of a Wildfire, Fuelbreaks, and Recently Burned Areas1

The Wheeler Fire #2 on the Los Padres National Forest, California, burned over 118,000 ac (47,755 ha) in 2 weeks. Several weather and physical factors contributed to the large size of this fire: drought conditions, high temperatures, erratic winds, low humidity, steep topography, poor access, and continuous stands of chaparral. This fire presented the rare opportunity for evaluating the coincidence of a wildfire, fuelbreaks, and recently burned areas. Observations indicate that the spatial relationships of fuelbreaks, roads, prescribed burns, and wildfires are important determinants of fire behavior and growth, and they merit special consideration in fuels and fire management planning. More case study documentation would provide fire managers with valuable information for developing guidelines on how to approach similar problems, under the same or different conditions. West. J. Appl. For. 2(2):55-58, April 1987.