Characterizing fuel treatment effectiveness in Utah

Background/Question/Methods: Fuel reduction treatments are regularly used by land managers to mitigate the negative effects of large, severe wildland fires. Depending on the habitat type, fuel treatment objectives may seek to decrease final wildfire size and/or decrease burn severity. Despite their wide-spread application and expenses in the millions, there is a lack of consensus on the effectiveness of fuel treatments in modifying wildfire behavior on large spatial scales. In part, this is due to the fact that logistically only a small portion of the landscape can be treated and an even smaller percentage of fuel treatments are actually encountered by wildfires. This study used broad-scale spatial analysis and existing datasets to characterize how wildfires have interacted with real fuel treatments state-wide in Utah. Wildfire and fuel treatment perimeter data were provided by the Bureau of Land Management and Forest Service. The study included 4,016 fuel treatments and 1,726 wildland fires from 1997 to 2019. For treatments that were intersected by wildfire, effectiveness was determined based on metrics associated with wildfire size and burn severity. The likelihood that a wildfire would encounter a fuel treatment, and conversely, that a fuel treatment would be encountered by a fire, were also estimated.

Results/Conclusions: We found that 4.3% of treatment footprint acres were subsequently burned by wildfire, and 1.3% of wildfire acres encountered a treatment unit. Approximately 20% of treatments were 100% burned, but 80% were only partially burned, suggesting that most treatments are effective in slowing or stopping the spread of wildfire. We evaluated burn severity in forested areas, and found that severity was reduced in treated areas, on average, compared to untreated areas of fires. Larger and more recent fuel treatments were more effective in reducing wildfire size and burn severity. Finally, units that consisted of a single treatment were less effective in reducing wildfire effects than units that had received multiple treatments. Our results suggest that fuel treatments have low probability of being tested by wildfire, but when fires encounter treatments they tend to meet objectives of slowing, stopping, or reducing the severity of wildfire.