Five years ago, the Caldor Fire consumed more than 200,000 acres across the Sierra foothills and Echo Summit, largely destroying the town of Grizzly Flats in El Dorado County.
It was the second wildfire to crest the Sierra Nevada that year, a feat previously thought to be unprecedented.
But as the Caldor Fire burned through, two communities — Christmas Valley and Meyers, near South Lake Tahoe — were spared from devastation due to significant fuel-reduction treatments.
The event became known as the “Christmas Valley Miracle,” and was studied to learn how different treatment methods worked best in preventing disaster, and how they influenced future forest management.
Hugh Safford is a vegetation and fire ecologist with UC Davis, whose home in Meyers was threatened by the Caldor Fire.
Susie Kocher is a forest advisor with the UC Cooperative Extension focused on the Central Sierra, including El Dorado, Calaveras, Amador and Tuolumne counties.
They spoke with Insight Host Vicki Gonzalez about efforts to reduce fuels and thin forests to cut down on wildfire severity, as well as how forests are responding.
This interview has been edited for length and clarity.
Interview highlights
How has wildfire danger in the Tahoe Basin changed over the years and evolved?
SAFFORD: The forests of the Tahoe Basin have an inextricable relationship with fire. Jeffrey pine is the dominant tree. It's extremely fire tolerant; it has thick bark, prunes its lower branches to interrupt fire spread to the canopy. Its cones are thick-scaled and well insulated. And interestingly, its foliage is also among the most flammable conifer foliage known. It’s therefore a promoter of low and fast-moving, but hot, fires. These kill the young of its competitors, like white fir and incense cedar.
Most of the Jeffrey pine and mixed conifer forest in the Lake Tahoe Basin was cut down in the late 19th century to support silver mining in Nevada. When you combine this with the fact that in the early 20th century, fire was removed as an ecological process in the Tahoe Basin by imposition of strict control policies, removal of the Washoe inhabitants, and banning of fire as a management tool, that led to huge changes in forest composition, structure, and function.
Forests that were once open and dominated by large fire-tolerant trees are now dense, and they're dominated by young and middle-aged stands of fire intolerant trees. It's been replaced by an environment that's conducive to large uncontrollable configurations that are a threat to not just human health and safety, but environmental health as well.
Your home in Meyers was in the path of the Caldor Fire. Take us back to that moment when the fire crested the Sierra and was headed toward these communities?
SAFFORD: I live part-time in Meyers. I worked for the Forest Service for 20 years as an ecologist, and I have close personal and professional connections in the basin with agencies and people. Our home was in the evacuation zone when the fire reached the crest — I think it must have been Aug. 30. I was out of town actually, but my son was living there. We told him to get out of town before things got crazy, so luckily he left town a few days earlier and our home survived the fire. But in our case the flames came within about 700 feet of our house.
Given the importance of the event, and the close proximity of the fire to my home, and the very obvious effects of forest fuel reduction… there was no question that I was going to get involved in studying what happened. We were really lucky to get funding to actually assess the effects of the forest because that “Christmas Valley Miracle” really was an extraordinary thing. We were just astounded to come back and realize that, you know, not a single structure had been lost in fire. It was incredible.
A study you authored late last year found three key findings about what protected Christmas Valley and Meyers. What were those?
SAFFORD: We were interested in looking at what the effects of the fire had been on the forest, and the extent to which pre-fire fuel reduction and forest management had had any positive effects. We found in general that across all the different kinds of forest treatment that the Forest Service had pulled off, trees were about three times more likely to survive in treated areas than in untreated areas. In most of the measures that we made of what we call “fire severity” — the extent to which tree trunks were burned, or canopy was lost [or] scorched — we found that the treatments generally had positive impacts.
I will note that one of our findings was a little unfortunate, but not unexpected. There’s such a backlog of fuel piles on the ground in a lot of the Lake Tahoe Basin because of the frenetic pace of fuel reduction work. Having those on the ground actually led to unexpectedly higher fire severity in some parts of the fire perimeter as well. The other interesting thing we found was that it didn't necessarily need to include prescribed fire to be extremely effective. This has been one of the mantras of the last 10-15 years — the most effective treatments tend to involve mechanical and hand thinning, then followed by prescribed fire which does the best job of cleaning up the fine fuels on the forest surface.
We found that a number of different mechanical and hand entries including mastication — a chipping treatment — worked really well at ameliorating fire behavior.
Is that a safer option? There are cases where a prescribed fire can turn into a wildfire.
SAFFORD: Prescribed fire is a really cost-effective way to reduce forest fuels. And by using fire, we also can reintroduce some of the beneficial outcomes of fire that we've lost during this fire-exclusion period.
At the same time, a lot of managers have a lot of reservations about using prescribed fire. The Lake Tahoe Basin Management Unit has for many decades been very reluctant to do what we call “broadcast burning,” which is to allow prescribed fire to move unfettered through the forest understory. Rather, they've fallen back on pile burning. Most of the work that gets done there involves some mechanical thinning and/or hand thinning, and that’s pretty common. It’s a bit less risky, but it doesn’t do the same kind of job in reducing the fine fuels that are so important to driving fire behavior. In fact, some of those treatment types can actually increase surface fuels.
Christmas Valley and Meyers are widely considered to have been “successes” during the Caldor Fire, but could things have gone better?
SAFFORD: The research we'd done, it was similar to results from studies we did in the early 2000s on the Angora Fire, which burned a couple hundred homes just west of South Lake Tahoe and was a real turning point in the way that people thought about fuel reduction.
In both cases we found that where fuel piles hadn't been removed, there was a higher fire severity. That creates some issues for environment impacts but also in the ability to control fire, and protect humans and infrastructure. Nothing comes without complication, Lake Tahoe Basin [Management Unit] actually cuts somewhat larger trees than most units do, so it takes a couple years to get things dried to where they can be burned. There is no dedicated burn crew on the Lake Tahoe Basin Management Unit. In fact, there isn't one on most forest service units — what I think is a big issue. Therefore, the unit has to rely on the fire suppression workforce to get the work done.
But in a busy fire year they're not around, they could be fighting fires in Arizona or Kentucky or Alaska. A large part of that staff is seasonal so they get laid off in the fall, which is just when the burn season begins. Lake Tahoe Basin has been very ahead of the ball trying to get this work done, and as a result of it the piles just keep piling up. At any given time you might have 100,000 or more fuel piles on the ground. I think our assessment of the impacts of the burn piles in the Caldor Fire and Angora Fire are finally starting to have some impact on the way the Lake Tahoe Basin Management Unit and the other agencies think about disposing of piles.
Forests and post-fire resilience
Tahoe is a unique place, shared between Nevada and California. How does that affect wildfire management and mitigation?
KOCHER: We have the benefit of a lot of eyes and a lot of resources. A lot of our local agencies have really worked hard to tell Tahoe's story, bring lawmakers here and get the funding to do the fuels reduction. It’s got, I would say, the best-managed forest in the Sierra Nevada.
I moved to South Lake Tahoe after spending 13 years living in Greenville, in Plumas County. That was the summer of 2021 when the Caldor Fire started, the Dixie Fire started in July, and Greenville burned down on Aug. 4. I evacuated from the Caldor fire too for two weeks, and I really didn't think I would see my house again.
I think of it as an interesting comparison. I think a lot of the rest of the rural Sierra has not really had the resources or leadership to do as aggressive thinning as needs to be done for the future to make sure that our forest communities can survive.
There have been so many wildfires in recent years from the Caldor Fire to the Kings Fire, and even the 2007 Angora Fire. How are forests recovering in these areas after almost two decades of fires?
KOCHER: I think it's actually Hugh's research that looked at what percentage of fires were high severity before settlement, and the number is around 7%. Our tree species are generally adapted to being in a landscape where there are living seed trees nearby. If they’re not, seeds don't come in and trees don't regenerate. When there was seven percent of the landscape burning at high severity, you’d have larger patches of shrubs. But now it's around 36% with huge patches, thousands of acres, with no living trees. In those areas without a seed tree, we have a substantial concern that [this] forest will not regenerate on their own. In those contexts, it’s really important to replant.
We are seeing conversion of some of our forests in the Southern Sierra. It's as high as 30% of formerly forested land [that] is now shrubland, with not a lot of hope that these forests will regenerate without human intervention. We changed the system by suppressing all the fires, and now the system needs us to replant. I find that that's not necessarily something that most people understand. Private forest landowners, even the public concerned about what the Forest Service is doing, don't necessarily understand that without some interventions in many areas, there won't be forests.
A recent report by the California Wildfire and Forest Resilience Task Force showed that from the fires between 2020 and 2024, there were 1.6 million acres in the state in need of reforestation, but one million had not been reforested. Before the year 2000, the Forest Service used to reforest around 18%; now they’re only reforesting about 8% of their land because there’s so much more being burned. There’s just not the capacity to get those areas treated. On private forest land it's around 300,000 acres that need reforestation since 2020.