Severe wildfires in the Sierra Nevada and southern Cascade forests are increasing and burning at unprecedented rates compared to the years before European and American settlement, according to a study by UC Davis’ Safford Laboratory and collaborators. . These rates in particular have soared over the past decade.
For this study, published in the journal Ecospherescientists analyzed fire severity data for seven major forest types from the U.S. Forest Service and Google Earth Engine.
They found that in low- and mid-elevation forest types, the average annual area of low-to-moderate burning has decreased from more than 90% before 1850 to 60-70% today.
At the same time, the area covered by serious fires has nearly quintupled each year, from less than 10 percent to 43 percent today. (Severe burns are those in which more than 95 percent of the above-ground tree biomass has been destroyed by fire.)
That ratio is grossly out of balance, said lead author and UC Davis project scientist John N. Williams.
“We’re seeing more ‘bad fires’ and fewer ‘good fires,'” said Williams, coordinator of California’s Regulation Fire Monitoring Program. “Any comfort we get from thinking ‘at least we’re burning more than before’ isn’t real comfort because it usually comes in the wrong form.”
good fire bad fire
Many fire ecologists speak of the need to burn more land by putting “good fires” on the ground, such as through prescribed burning, while preventing “bad fires”. In forests such as oak groves, ponderosa pine, and mixed coniferous forests, good fire refers to low- to moderate-severity burning to which the dominant species is adapted. They are often ignited by lightning or people to enrich and restore the land. Many of these fires were lit by Native Americans through the practice of cultural burning before the mid-19th century.
Before 1850, California burned far more land each year than it does today. The study suggests that the gap is starting to close. Unfortunately, more blazes include destructive, high-severity fires.
This represents the most worrying result, the authors say: The average area of severe burns in the region now exceeds the best estimates of severe burns that occurred before European and American colonization, although modern overall burns are much lower.
“At the current and even projected pace of forest management by federal and state agencies, the amount of forest that is treated or restored will be a drop in the bucket compared to what is needed, compared to the vast unmanaged area that will be burned. UC Davis Fire Ecology “I’m not exaggerating when I say that the existence of California’s montane coniferous forests is at risk, especially in the state’s south. “
grim decade
Nine of California’s 10 largest wildfires occurred within the past decade. The state’s record-breaking fire year in 2020 — nearly 9,900 fires burned 4.3 million acres — was the only year in which the annual area burned exceeded historic levels, but most of those fires were severe.
This trend is particularly worrisome, the authors say, because most of the affected low- and middle-elevation forest types are adapted to burn at low to moderate severity. Excessively severe fires in these forests can damage the landscape and the habitats and ecosystem services it provides.
Additional research by the Safford lab at UC Davis and partners has shown that the negative impacts of severe burning in these forest types have serious implications for biodiversity, carbon storage, soil biogeochemistry, air quality and forest regeneration. and lasting negative effects.
get the right combination
The study’s findings highlight the need for management practices that better balance fire prevention with proactively reducing forest fuels and increasing resilience to climate change and other ecological disturbances.
“We need to burn more fuel each year, but we need the right mix,” Williams said. “If we want to restore forests and their natural ecological processes, the current trend is going in the wrong direction.”
Other co-authors of the study include Nic Enstice of the California Department of Conservation, Zack Steel of the USDA Forest Service’s Rocky Mountain Research Station and Alison Paulson of the USDA Forest Service’s Humboldt-Toyabe National Forest.
