Intense wildfires are increasing in the Sierra Nevada and Southern Cascade forests, and they have been burning at rates unprecedented compared to the years before European-American settlement, according to a study from the Safford Lab at the University of California, Davis and collaborators. These rates have increased particularly over the past decade.
For the study published in the journal OceanScientists analyzed fire intensity data from the US Forest Service and Google Earth Engine across seven major forest types.
They found that in low- and middle-altitude forest types, the average annual area burned at low-to-moderate intensity fell from more than 90 percent before 1850 to 60-70 percent today.
At the same time, the area burned annually with very severe intensity has increased fivefold, rising from less than 10% to 43% today. (High-severe burns are those in which the fire kills more than 95% of the trees’ above-ground biomass.)
Lead author and UC Davis project scientist John N. Williams said that ratio is deeply unbalanced.
“We are seeing more of the ‘bad fire’ and less of the ‘good fire,’” said Williams, coordinator of the California State Specific Fire Watch Program. “Any consolation we get from the idea that we are at least burning more than we used to, is not really a consolation because it often comes at Form the wrong kind of fire.”
Good fire, bad fire
Many fire ecologists talk about the need to burn more acres by putting a “good fire” on the ground, such as the burn described, while preventing the “bad fire.” In forests such as those of oak, yellow pine, and mixed pine, a good fire indicates a low to moderate burn that the dominant species are adapted to. They are usually ignited by lightning or by people to enrich and restore the earth. Many of these fires were set by Native Americans prior to the mid-19th century through the practice of cultural burning.
Prior to 1850, more land was burned each year in California than it is today. The study indicates that the gap is closing. Unfortunately, much of what is burned involves a very harmful and dangerous fire.
This represents the most troubling finding, the authors say: The average area of high-risk burn in the region is now higher than the best estimates for high-risk burn that occurred before Euro-American settlement, despite total burning in modern times. Still much less.
“At current or even projected rates of forest management by federal and state agencies, the amount of forest treated or restored will be a group decrease compared to need, and compared to the huge unmanaged areas that would burn,” said senior author Hugh Safford, senior ecologist at UC Davis and senior author. “Often very dangerous,” scientists at the environmental public utility company Vibrant Planet said. “I am not exaggerating when I say that the very existence of mountain coniferous forests in California is at risk, especially in the southern part of the state.”
Nine of the 10 largest wildfires occurred in California during the past decade. The state’s record-breaking fire year of 2020 — when nearly 9,900 fires burned 4.3 million acres — was the only year the annual area burned exceeded historic levels, but much of that burned badly.
The authors say this trend is particularly worrisome because most affected low-to-medium-elevation forest types are adapted to low-to-moderate-intensity burn. Extremely intense fires in these forests can damage landscapes and the habitats and ecosystem services they provide.
Other research by the Safford Lab at UC Davis and partners has shown that the negative effects of intense burning in these types of forests are serious and long-term on biodiversity, carbon storage, soil biochemistry, air quality, and forest regeneration.
Get the right mix
The study findings highlight the need for a better balance between fire exclusion and management practices that proactively reduce forest fuels and increase resilience to climate change and other environmental disturbances.
“We need to burn more every 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.”
Additional co-authors of the study include Nick Enestes of the California Department of Conservation, Zach Steele of the USDA Forest Service’s Rocky Mountain Research Station, and Allison Paulson of the USDA’s Humboldt-Tuapeh National Forest.