Fact sheet: Do fuel treatments reduce fire severity in ponderosa pine forests? Tree mortality patterns one year after the Wallow Fire

In recent decades, more frequent, larger and more severe wildfires have erupted in dry forest types (e.g., ponderosa pine) across the western United States (Westerling et al. 2006). Given predictions for a warmer and drier climate across the interior West, such fires are likely to continue. In an effort to mitigate large, severe wildfires, fuel treatments are under way across the West. The priority sites for these fuel treatments are in the wildland urban interface (WUI), where relatively small treatment units are concentrated around towns and dispersed settlements (Ager et al. 2010). There is a growing body of anecdotal and empirical evidence that suggests WUI treatments are effective for reducing damage to communities (Martinson and Omi 2013, Safford et al. 2009), but it remains unclear whether these treatments can mitigate today's uncharacteristically large and severe wildfires. Computer modeling shows that by failing to invest in treatments beyond the WUI, high burn severities will persist at the greater landscape level (Waltz 2012). In this study, ERI researchers used a post-wildfire field measurement approach to study and describe the effectiveness of WUI hazardous fuels treatments in reducing fire behavior and conserving forest resiliency during the Wallow Fire, a 538,000-acre uncharacteristically, high-severity wildfire that burned in Arizona in 2011. Our primary goals were to: 1) measure changes in burn severity as the wildfire transitioned from high-severity untreated to treated areas, 2) compare ponderosa pine tree mortality and basal area (BA) loss across paired treated and untreated areas, and 3) compare post-fire stand structure, tree regeneration, snag density, and coarse woody debris between treatments with respect to natural ranges of variability (NRV)