Wildfire Can Benefit Landscapes and Reduce Threats to Local Communities
Forests in California are vulnerable to large, severe wildfires that have the potential to harm human communities, habitat for sensitive wildlife species, and water resources. Research to date in the Western United States indicates that fire size and severity have been increasing during the past several decades.
On the four national forests in northwestern California, a Forest Service study assessed the trends and patterns in fire size and frequency from 1910 to 2008 with all fires greater than 98 acres, and the percentage of high-severity in fires from 1987 to 2008 with all fires greater than 988 acres. From 1910 to 2008, mean and maximum fire size and total area burned annually increased, but the scientists found no trend over time in the percentage of high-severity fire from 1987 to 2008.
The percentage of high-severity fire in conifer-dominated forests was generally higher in areas dominated by smaller diameter trees than in areas with larger diameter trees. Years when larger fires with the greatest area burned were produced by regionwide lightning events and characterized by less winter and spring precipitation than during years dominated by smaller human-ignited fires.
The overall percentage of high-severity fire was generally lower in years characterized by regionwide lightning events and appears to be quite similar to prefire suppression-era severity patterns largely because the fires burned mostly under less-than-severe conditions. In contrast, large human-caused fires generally escape under severe conditions and result in greater proportion of high severity.
Our results suggest that under conditions typical of widespread lightning-fire outbreaks, wildfires could be more extensively used by land managers to achieve ecological and management objectives in northwestern California.