Extreme Colorado 2020 fires: remotely sensed burn severity influenced by treatments, forest types and days of burning

Forest managers are faced with escalating size, severity, and cost of wildfires. To mitigate this, U.S. federal land management agencies are increasing forest treatments such as mechanical thinning and prescribed fire. While there is a growing body of work on treatment-wildfire interactions, treatment impacts in increasingly extreme wildfire situations remain unknown. Here we examined how treatments and previous wildfires influenced remotely sensed burn severity across four 2020 wildfires in Colorado that burned over 238,000ha, 10,000ha of which were treated or experienced previous wildfires. Our analyses show lower observed burn severity in treated areas across forest types and day of burning conditions. Treatments were associated with the lowest severity on days with lower wind speeds and days of limited fire growth, conditions indicative of less extreme fire weather. Additionally, treatments correlated with the lowest burn severity in lower-elevation, fire-resistant dominated forest types. This indicates both a difference in the predominant treatment types and extent of treatments in these forests and latent forest structure results in variable burn severity. This study demonstrates the importance of acting strategically about where and what types of treatments, as well as past wildfires, will mitigate future ecological impacts of wildfires under changing fire regimes.