A new Environmental Research Letters study reveals that the severity of the state’s wildfires has rapidly increased over the last several decades, contributing to greater forest loss than would have been expected from past increases in burned areas.
“Fire severity increased by 30% between the 1980s and 2010s,” said Jon Wang, an assistant professor at the University of Utah School of Biological Sciences and former postdoctoral researcher at the University of California Irvine Department of Earth System Science. This means that for every acre of forest scorched by fire, the damages to mature trees are considerably higher than what occurred in the average fire several decades ago.
Jon Wang conducting field research in Norway. Photo credit: Acacia England, U.S. Forest Service
“When fire moves through an area on the forest floor, often mature trees survive and, in some situations, they may thrive from fire effects on nutrient cycling,” said study co-author James Randerson, professor in the UC Irvine Department of Earth System Science. “The new research suggests more fire is jumping into the tree crowns, causing more damage and tree mortality.”
Randerson added that wildfires also have moved into new areas with denser and more vulnerable forests. Those areas include northern mountain and coastal regions that may have been protected in the past by cooler summers and higher levels of surface moisture.
“Forest exposure has increased 41% over the past four decades, suggesting denser forests are now more vulnerable to wildfire,” said Wang, who joined the U last year and is the principal investigator for the Dynamic Carbon and Ecosystems lab.
The question Wang and his team wanted to answer was how much-rising tree cover loss in California is due to increases in total area burned, how much of the loss is due to increasing wildfire severity, and how much is due to fire moving into new areas with denser forests.
“There’s a pretty shocking map of just how much these fires have expanded into northern California forests,” Wang said. “There’s just a lot more fire in these northern forests than there used to be. Climate change allows severe fires to affect forests that once tolerated milder fires.”