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Unprecedented Levels of High-Severity Fire Burn in Sierra Nevada Forests

The 鈥榃rong Kind of Fire鈥 Is Burning Compared to Historical Patterns

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Firefighter walks along highway with flames to his side during Creek Fire response in 2022.
A firefighter helps containment efforts during the Creek Fire response in 2020. (USDA, Pacific Southwest Forest Service)

Quick Summary

  • The proportion of 鈥済ood鈥 to 鈥渂ad鈥 fire in the Sierra Nevada is severely out of balance compared to historical rates.
  • Before 1850, many more acres burned each year compared to today.
  • More than 90% of historic fire burned at low-moderate severity, which is beneficial for forest health.
  • Today, the pattern is flipped. Less land burns, but up to 43% of what does burn comes as damaging, high-severity fire.

High-severity wildfire is increasing in Sierra Nevada and Southern Cascade forests and has been burning at unprecedented rates compared to the years before Euro-American settlement, according to a study from the Safford Lab at the University of California, Davis, and its collaborators. Those rates have especially shot up over the past decade. 

For the study, , scientists analyzed fire severity data from the U.S. Forest Service and Google Earth Engine, across seven major forest types. 

They found that in low- and middle-elevation forest types, the average annual area that burned at low-to-moderate severity has decreased from more than 90% before 1850 to 60-70% today. 

At the same time, the area burned annually at high severity has nearly quintupled, rising from less than 10% to 43% today. (High-severity burns are those where more than 95% of aboveground tree biomass is killed by fire.)

Lead author and 69成人 project scientist John N. Williams said this ratio is severely out of balance.

鈥淲e鈥檙e seeing more 鈥榖ad fire鈥 and less 鈥榞ood fire,鈥欌 said Williams, who is the coordinator of the California Prescribed Fire Monitoring Program. 鈥淎ny consolation we鈥檇 get from the idea that, 鈥楢t least we鈥檙e burning more than we used to,鈥 isn鈥檛 really a consolation because it鈥檚 often coming in the form of the wrong kind of fire.鈥
 

John N. Williams in yellow protective clothing lights prescribed fire with drip torch in forest.
69成人 Project Scientist John N. Williams uses a drip torch to light a prescribed burn on Southern California Edison forest land at Shaver Lake in 2022. (Abner Kingman)

Good fire, bad fire

Many fire ecologists talk about the need to burn more acreage by putting 鈥済ood fire鈥 on the ground, such as through prescribed burning, while preventing 鈥渂ad fire.鈥 In forests like oak woodland, yellow pine and mixed conifer, good fire refers to the low-to-moderate severity burning that the dominant species are adapted to. They are typically ignited by lightning or by people to enrich and restore the land. Many such fires were set by Native Americans before the mid-19th century through the practice of cultural burning. 

鈥淚鈥檓 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.鈥  鈥 Hugh Safford, 69成人 forest ecologist

Before 1850, much more land burned each year in California compared to the present day. The study indicates that gap is beginning to close. Unfortunately, more of what is burning comprises damaging, high-severity fire.

That represents the most concerning result, say the authors: The average area of high-severity burning in the region is now above the best estimates of high-severity burning that took place before Euro-American settlement, even though overall burning in the modern day is still much lower.
 

gray and white bar graph of acreage burned from 184-2020
This bar graph from the Ecosphere study shows the rising trend in burned area since 1984 and how it compares to pre-Euro-American settlement estimates. (Safford, et. al.)

鈥淎t 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,鈥 said senior author Hugh Safford, a 69成人 fire ecologist and chief scientist of environmental public benefits corporation Vibrant Planet. 鈥淚鈥檓 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.鈥

A severe decade

Nine of California鈥檚 10 biggest wildfires occurred within the past decade. The state鈥檚 record-breaking 2020 fire year 鈥 when nearly 9,900 fires burned 4.3 million acres 鈥 was the only year in which the annual area burned exceeded historical levels, but much of that burned at high severity. 

The authors say this trend is especially concerning because most of the low- to middle-elevation forest types affected are adapted to low-to-moderate severity burning. Excessively severe fires in these forests can harm landscapes and the habitat and ecosystem services they provide. 

Other research carried out by the at 69成人 and its partners has shown that negative effects of severe burning in these forest types are serious and long-lasting to biodiversity, carbon storage, soil biogeochemistry, air quality and forest regeneration. 

Getting the right mix

The study鈥檚 results highlight the need to better balance fire exclusion with management practices that proactively reduce forest fuels and increase resilience to climate change and other ecological disturbances. 

鈥淲e need to burn much more each year, but we want the right mix,鈥 Williams said. 鈥淭he current trend is going in the wrong direction if we want to restore forests and their natural ecological processes.鈥

The study鈥檚 additional co-authors 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.

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Media Contacts:

  • John N. Williams, 69成人 Environmental Science and Policy, 530-744-9081, jnwill@ucdavis.edu 
  • Kat Kerlin, 69成人 News and Media Relations, 530-750-9195, kekerlin@ucdavis.edu

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