Bark beetle outbreaks, wildfires and defensible space: how much area do we need to treat to protect homes and communities?

Extensive beetle outbreaks across western North American forests have spurred debates about how to best protect communities from wildfire. Previous work has found that fuels in the wildland–urban interface and especially in the defensible space (40-m radius) around structures are the most important determinants of the flammability of structures during wildfire. We: (1) examined the extent of outbreaks in the western US and their intersection with the wildland-urban interface and its surrounding area and (2) calculated the combined area of defensible space around all wildland-urban interface housing units in the western US. This analysis indicates that: (1) >98% of areas affected by outbreaks are in remote areas rather than in the wildland-urban interface and (2) in the context of limited resources and the goal of protecting homes and communities from wildfire, the area required to create defensible space around all homes in the wildland-urban interface of the western US (which effectively reduces fire risk to structures) is substantially less than that needed to treat all beetle-affected forests (which does not reduce fire risk to structures as effectively). Thus, focussing fuel-reduction treatments in the immediate vicinity of homes and communities rather than in remote beetle-affected forests would be more effective at reducing fire risk to those structures and would incur lower financial and ecological costs.