Human ignitions on private lands drive USFS cross-boundary wildfire transmission and community impacts in the western US

Abstract

Wildfires in the western United States (US) are increasingly expensive, destructive, and deadly. Reducing wildfire losses is particularly challenging when fires frequently start on one land tenure and damage natural or developed assets on other ownerships. Managing wildfire risk in multijurisdictional landscapes has recently become a centerpiece of wildfire strategic planning, legislation, and risk research. However, important empirical knowledge gaps remain regarding cross-boundary fire activity in the western US. Here, we use lands administered by the US Forest Service as a study system to assess the causes, ignition locations, structure loss, and social and biophysical factors associated with cross-boundary fire activity over the past three decades. Results show that cross-boundary fires were primarily caused by humans on private lands. Cross-boundary ignitions, area burned, and structure losses were concentrated in California. Public lands managed by the US Forest Service were not the primary source of fires that destroyed the most structures. Cross-boundary fire activity peaked in moderately populated landscapes with dense road and jurisdictional boundary networks. Fire transmission is increasing, and evidence suggests it will continue to do so in the future. Effective cross-boundary fire risk management will require cross-scale risk co-governance. Focusing on minimizing damages to high-value assets may be more effective than excluding fire from multijurisdictional landscapes.

Yearly population data at census tract level revealed that more people are now living in highly fire-prone zones in California, USA

“…Moreover, the population increase signifies the expansion of private land, raising concerns as private land fragmentation interferes with public land and undermines mitigation efforts. Given that most wildfires initiate on private land (Downing et al 2022), the prevalence of human-induced fires, combined with personal property serving as a wildfire starting point, underscores population change as a significant factor contributing to heightened wildfire risk.…”

“…This trend has prompted insurance companies to deny coverage to residents in high wildfire-risk zones throughout California (Kramer et al 2019, Gonzalez 2023. The substantial proportion of wildfires originating from private land within the WUI intensifies the exposure of properties to risk (Downing et al 2022). Additionally, the density of structures in interface communities, coupled with inadequate response time such as fire-fighting compliant road access, poses challenges for preventing loss of buildings (Glickman and Babbit 2001).…”

Toxicity of Wildland Fire Retardants to Rainbow Trout in Short Exposures

“…Wildland fires in the United States are becoming more intense and more frequent in the 21st century (Dennison et al, 2014; Senande‐Rivera et al, 2022). Fires on public lands result in economic and recreational damage and can impact surrounding communities if the spread of the fire is not contained (Bawa, 2017; Downing et al, 2022). Also, fires can be ignited on private lands and cross boundaries into public land, causing widespread impacts.…”

Higher incidence of high‐severity fire in and near industrially managed forests

“…Most of these studies examined only a single fire event, with very little work done at larger geographic scales on cross‐boundary risk associated with ownership type or management approach (but see Downing et al . 2022). Here, our goal was to quantify the impact of land ownership on the incidence of high‐severity fire, conditional on fire occurrence, through large‐scale analyses of wildfires in California.…”

“…Several have demonstrated reduced fire severity and area burned in industrially managed forests (Lyons-Tinsley and Peterson 2012; Starrs et al 2018), whereas others have reported increased severity (Zald and Dunn 2018). Most of these studies examined only a single fire event, with very little work done at larger geographic scales on crossboundary risk associated with ownership type or management approach (but see Downing et al 2022). Here, our goal was to quantify the impact of land ownership on the incidence of high-severity fire, conditional on fire occurrence, through large-scale analyses of wildfires in California.…”