According to a study by the Safford Lab at the University of California, Davis and its collaborators, high-severity wildfire is growing in the Sierra Nevada and Southern Cascade forests and has been burning at unprecedented rates compared to the years before Euro-American settlement. Those rates have especially shot up over the past decade.
Researchers examined data on fire severity across seven major forest types for the study, which was published in the journal Ecosphere. The data came from the U.S. Forest Service and Google Earth Engine.
They discovered that the average yearly area that burned with low-to-moderate severity has declined in low- and middle-elevation forest types from more than 90 percent before 1850 to 60-70 percent now.
At the same period, from less than 10% to 43% now, the area burned annually at high severity has nearly quadrupled. (High-severity burns are those where more than 95% of aboveground tree biomass is killed by fire.)
Lead author and UC Davis project scientist John N. Williams said this ratio is severely out of balance.
“We’re seeing more ‘bad fire’ and less good fire,” said Williams, who is the coordinator of the California Prescribed Fire Monitoring Program. “Any consolation we’d get from the idea that, ‘At least we’re burning more than we used to,’ isn’t really a consolation because it’s often coming in the form of the wrong kind of fire.”
Good fire, bad fire
Many fire ecologists emphasize the need to burn more land while preventing “bad fire” and putting “good fire” on the ground, such as through managed burning. The term “good fire” refers to low to moderate-severity burning that the main species are accustomed to in forests like oak woodland, yellow pine, and mixed conifer.
At current or even projected rates of forest management by federal and state agencies, the amount of forest treated or restored is going to be a drop in the bucket compared to the need, and compared to the huge unmanaged areas that are going to burn, often at high severity. I’m not exaggerating when I say that the very existence of montane conifer forest in California is at risk, especially in the southern part of the state.
Hugh Safford
Typically, they are lit on fire by lightning or people to animate and better the region. Native Americans frequently sparked these kinds of fires by setting cultural artifacts on fire before the middle of the 19th century.
California burned a lot more land annually before 1850 than it does today. According to the report, the disparity is starting to close. Unfortunately, a larger portion of the fire is destructive, high-severity fire.
That represents the most concerning result, say the authors: Even if overall burning in the contemporary era is still substantially lower, the average area of high-severity burning in the region is currently higher than the best estimates of high-severity burning that occurred before to Euro-American settlement.
“At current or even projected rates of forest management by federal and state agencies, the amount of forest treated or restored is going to be a drop in the bucket compared to the need, and compared to the huge unmanaged areas that are going to burn, often at high severity,” said senior author Hugh Safford, a UC Davis fire ecologist and chief scientist of environmental public benefits corporation Vibrant Planet. “I’m not exaggerating when I say that the very existence of montane conifer forest in California is at risk, especially in the southern part of the state.”
A severe decade
Nine of California’s 10 biggest wildfires occurred within the past decade. The only year in which the annual area burned exceeded historical levels was the state’s record-breaking 2020 fire year, when nearly 9,900 flames burned 4.3 million acres, much of it at a high severity.
The majority of the low- to middle-elevation forest types affected are adapted to low- to moderate-severity fire, according to the authors, who find this trend particularly alarming. Extremely destructive fires can impair the landscape, the habitat, and ecosystem services that these forests offer.
Other studies conducted by the Safford Lab at UC Davis and its collaborators have demonstrated that significant burning in various forest types has detrimental consequences on biodiversity, carbon storage, soil biogeochemistry, air quality, and forest regeneration that are serious and long-lasting.
Getting the right mix
The findings of the study demonstrate the necessity of striking a better balance between fire exclusion and forest fuel reduction strategies that proactively boost resistance to climate change and other ecological disturbances.
“We need to burn much more each year, but we want the right mix,” Williams said. “The current trend is going in the wrong direction if we want to restore forests and their natural ecological processes.”
The study’s additional coauthors include Nic Enstice of the California Department of Conservation, Zack Steel of the USDA Forest Service Rocky Mountain Research Station, and Alison Paulson of USDA Forest Service Humboldt-Toiyabe National Forest.
