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Wildfire Trends Across the Western US: Forest Fires Have Increased in Size, Severity, and Frequency Across Western Forests

Author(s): Tzeidle N. Wasserman
Year Published: 2020

Wildfire is a natural disturbance and ecological process in forested ecosystems across the western United States. However, warmer temperatures, frequent droughts, and legacies of past land management are impacting western forests, leaving them at a higher risk for large, uncharacteristic wildfire that has dramatic impacts on ecosystems and nearby communities. Historical fire regimes were a mix of human and lightning-ignited fires, and no longer operate at the time and spatial scales they did historically. In many areas, this has resulted in an increased density of trees on the landscape, increased fuel availability, and less diverse understory vegetation communities (Allen et al. 2002). Wildfire across the western US has increased in size, frequency, and severity since the 1950s. These changes are closely linked with increases in temperature and an increased frequency and intensity of drought (Peterson et al. 2013). Historically, frequent low to moderate-severity fires dominated the fire regime in many western forests, maintaining low-density forests with larger trees (Allen et al. 2002). A history of fire exclusion, logging activity, grazing, and invasive species has led to an uncharacteristic build-up of forest fuels in many areas, increasing the susceptibility to large-scale, high-severity wildfire. The US has a history of fire suppression efforts that has exacerbated the problem by increasing the density of trees and fuel availability, and reduced the overall area burned by wildfires to levels that are below those that occurred before the beginning of the 20th century (McKelvey et al. 1996, Sugihara et al. 2006, Stephens et al. 2007). The western US is also experiencing larger, more severe fires that are often near communities. In recent decades, the build-up of forest fuels, a warmer and drier climate, and expansion of the wildland-urban interface (WUI) into forested areas has changed western landscapes and increased wildfire hazard. Federal policy and management have primarily focused on fire suppression and more recently on fuels reduction on some federal lands. Forest restoration and fuels reduction projects have had positive ecological impacts; however, the pace and scale of forest treatments is not keeping up with heightened wildfire activity across the West.

Citation: Wasserman, Tzeidle N. 2020. Wildfire trends across the western US: forest fires have increased in size, severity, and frequency across western forests. ERI White Paper-Issues in Forest Restoration. Ecological Restoration Institute, Northern Arizona University. 10 p.
Topic(s): Fire Behavior, Fire & Climate
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 21368
FRAMES RCS number: 61334
Record updated: Jun 16, 2020