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Sierra Nevada forests have seen ‘unprecedented’ level of high-severity wildfires, study finds

Firefighters manage a back fire operation in Volcanoville, Calif., to fight the Mosquito Fire, Friday, Sept. 9, 2022.
Andrew Nixon
Firefighters manage a back fire operation in Volcanoville, Calif., to fight the Mosquito Fire, Friday, Sept. 9, 2022.

A new study from UC Davis researchers found that the proportion of good to bad fire in the Sierra Nevada — and much of California — is out of balance.

Wildfires have long been a facet of California’s ecosystem, as varied forest land covers much of the state and often benefits from some types of fire. Indigenous communities were using controlled burns to manage forests long before Europeans were part of the equation.

But a new study from UC Davis researchers found Sierra Nevada forests are facing more extreme wildfires, which could be bringing changes to ecosystems.

“We’re seeing more ‘bad fire’ and less ‘good fire,’” said John Williams, the lead author of the report. “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.”

Fires that burn more than 95% of organic matter above ground — classified as high-severity wildfires — have increased across California at “unprecedented rates” since the mid-19th century, the authors wrote.

The amount of low-to-moderate severity wildfires, which can be beneficial to forest ecosystems, also decreased during the same time period.

Authors noted that a large portion of those changes have been felt over the last decade, as the state has seen nine of its largest fires in recorded history.

CapRadio’s Randol White sat down with Williams, who is also the coordinator of the California Prescribed Fire Monitoring Program, to explain the study’s findings.

This interview has been edited for length and clarity.

What determines whether fire is good or bad in your study?

It comes down to what the ecosystem is adapted to: Different ecosystems are adapted to different kinds of fire and different mixes of fire. When I say mix, I'm talking about severity and how much mortality some fires cause.

What does this imbalance in good to bad fire mean for the Sierra's overall ecosystem moving forward?

Well, we have a number of different types of ecosystems in the Sierra. As you move up in elevation from the foothills all the way to the crest of the Sierra, we look at seven different forest types in that range. For example, in forests that are adapted to low-to-moderate severity fire, burning at really high severity … it can have pretty harmful effects on the ecosystem. It can change the species composition, it can change the water holding capacity, the carbon storage capacity, the animals and other plants that are adapted [to] that forest. It can really throw the system out of balance.

Is this primarily because the fires are burning hotter?

The fires are burning hotter, there's more fuel, and that's a result of a century-plus of fire suppression. Fire causes lots of damage that people don't like. And so in having policies that suppress all wildfire, we're also stopping kind of the lower, more frequent and more benign fire to both us and the ecosystem.

You mentioned the Sierra Crest, and over the past couple of years, we had instances that we hadn't seen before, where fire actually started on the western side of the crest and moved east over the crest.

Yeah, the Caldor Fire a couple of years ago, that was rare, maybe the only example we have of [a fire] going over the top of the crest. We've seen these mega-fires, these 100,000 to over a million acre fires burning in ways we don't have any evidence in the historical record [of happening] before. A lot of that is a result of this buildup of fuels that we're talking about. Some of it's due to longer fire seasons and climate change, but certainly that suppression and fire exclusion is a big part of it.

Is there a way to flip the equation so we see more good fire than bad in the years to come?

Yes, I mean, luckily we're not trying to solve nuclear fusion. I mean, if we really need more fire on the ground, whether that's in the form of wildfire that's burning in more benign conditions, or prescribed or cultural fire.

Is California moving in that direction?

It is. There's definitely recognition at state and federal levels that we need more prescribed fire, we need more cultural burning. But we're not even close to doing it on the magnitude where it needs to be [done]; making a dent in this backlog of fuels and restoring fire regimes to where they should be. There's a forest stewardship agreement between the state of California and the federal government where we're trying to get to a million acres [burned] a year. But we're still a long way from that, and we just need to be doing more of it.

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