The latest California tree mortality report from the US Forest Service shows more than 36 million trees died in the state’s forests during 2022, including more than a million standing in Tulare County’s groves. The number of dead trees represents a threefold increase in the mortality rate in a single year.
Rising Tree Mortality a 50-year trend
Tulare County accounted for 1.3 million of the state’s dead trees, mostly red and white fir trees attacked by beetles in Sequoia National Forest and the national parks. Fresno County saw an additional 1.9 million dead trees, according to the survey published in December. The survey was conducted between July and October and covered 39.6 million acres of forest statewide.
In total, the Forest Service found more than 2.5 million acres in the state are covered in dead trees, most still standing where they died. In Tulare County, about 120,000 acres have seen excess mortalities in 2022, a number almost identical to the 115,000 acres reported in 2021.
But the survey found nearly 500,000 more dead trees this year.
Jeffrey Moore, Aerial Survey Project Manager for the USFS, described the survey’s nature and history.
“It’s a general overview survey,” he said. “We’ve been doing it annually here in California since the 1970s, and more intensely in the last 20 years.”
Moore said the increase in tree mortality is part of a long-term trend that’s been evidence since before he joined the project in 1999. Until recently, the number of dead or dying trees mostly stayed steady while surveyors kept watch.
“From those very early years since I first got here, we would record maybe half a million trees freshly killed in a full year,” he said. “Then the drought happened.”
2016: The Deadliest Year
While arid conditions were prevalent for years before then, the historic drought affecting the Western US reached a peak in the mid-2010s.
“2016 was the most mortality we ever recorded, somewhere around 50,000,000 trees,” Moore said.
Including private land, in that year the survey counted a total of 61.7 million dead trees on 4.3 million acres across the state. Around 14 million of those dead trees were in Sequoia National Forest and Sequoia-Kings Canyon National Park.
The forests caught a break the next year, but it didn’t last.
“We had a nice wet year for ’17, then we slipped back into dry conditions,” Moore said.
That set the stage for a new deadly threat: insect infestation.
“The trees were never able to fully recover, because you went back into drought conditions, and the bark beetles were able to come in,” Moore said.
Saved by the Drought
In one of nature’s odd quirks, particularly harsh drought conditions in the forests of the Southern Sierra in 2016 are why local forests weren’t as hard hit last year as other areas of the state. The drought effectively thinned the forest.
“You had so many trees that had died from that event, so they had less competition,” Moore said. “More water for them, more space. It copied what a fire would do in some ways.”
That natural grooming also shows up in where Moore found the dead and dying trees attacked by the bark beetles.
“It is widely scattered on the landscape,” he said.
When the dead and weakened trees aren’t gathered in groves, it makes it less likely the beetle infestation will spread to neighboring pines and firs.
“There aren’t that many beetles around,” Moore said. “They use pheromones to target specific trees. They can actually smell the weaker trees.”
When the infested trees are spread out over the forest, the intensity of the pheromones is also lessened.
Climate Change at Play
By far, the species most affected by the die-off are red fir (15.2 million dead) and white fir (12.8 million dead). The die-off of firs is the highest ever recorded in California. Both fir species are native to Tulare County, as are the yellow pine (3.8 million dead) and Douglas fir (3 million dead).
The jump in white fir mortality represents a seven-fold increase since 2021. Moore said dead white fir trees accounted for the majority of the local tree death. Red fir was also affected here, but not as severely.
“Most red fir is in homogenous groves, long lived,” Moore said.
While white fir grows singly or in small groups at lower elevation, red fir prefers the colder, higher alpine areas of the High Sierra.
“The beetle tends not to do so well in this environment,” Moore said.
As average temperatures globally creep slowly ever upwards, that natural protection from bark beetles could be fading.
“With the change in climate, and this is just my opinion, in these higher temperatures the beetles are able to survive,” Moore said.
Three Months in the Air
To conduct the annual Aerial Detection Survey, Moore and his fellow spotter spend about three months flying in a small airplane over the state’s forests. From July 18 to October 7, the pair covered 39.6 million acres of California’s forests, both private and public lands.
“We fly as low as possible,” Moore said. “There are two of us. The other person is looking out the other side.”
What he witnessed this year was less drought damage here in the south and more in the northerly portions of the Sierra, starting around the Gold Country.
“The current drought situation is more centered in the Central Sierra and the northern interior, the greater Redding area,” he said.
Moore said he’s seeing a lot of fuel for potential future forest fires.
“The surviving trees on the landscape are more resilient. But you have a lot of dead trees that are coming down,” he said. “You have a lot of hazard trees. Firefighters are even reluctant to go into these areas (when they burn).”
Addressing the Hazard Trees
According to the Forest Service’s website on California tree mortality, the “epicenter” of tree deaths is three national forests: Stanislaus, Sierra and Sequoia here in Tulare County.
To reduce the death rate, the Forest Service is thinning hazard trees from areas of high use, such as roads, trails and campgrounds. Foresters are also thinning dense stands of trees to reduce susceptibility to beetle infestation, as well as encouraging a diversity of species and a wider age range. They’re also avoiding bringing down trees with natural drought tolerance.
These actions are intended to slow the spread of bark beetles and reduce the fire hazard.
“We’ve made lots of effort removing them, especially near residential areas,” Moore said.
Those efforts are being funded in part by the $65 billion 2021 Bipartisan Infrastructure Bill.
A change in the law governing forest management has also made the job a bit easier.
“Part of the situation also is we got new legislation that is allowing us to address some forest concerns as an emergency response,” Moore said. “We don’t have to go through the years-long process that would normally entail.”
But there are still challenges, like finding a private partner with a business plan to use the dead white fir trees, which are generally considered commercially useless in the lumber industry.
“The problem we’re dealing with is we have all this white fir that’s not worth anything. What do we do with all this white fir nobody wants?” Moore said. “What do we do with all this cellulose? It’s an energy source.”
Despite the recent heavy rains, moderate to severe drought still grips most of the Sierra in California. That combined with what the Forest Service calls “exploding” beetle populations means the state’s dead tree problem remains critical.