More than 36 million trees died across California last year — almost triple the number of trees that perished the year before — scattered across 2.6 million acres of the drought-ridden state.

The report, published Tuesday and conducted by the U.S. Forest Service, depicts a state that has been battered by drought, disease and insects that suck the life out of vulnerable trees. Tree mortality was particularly severe and widespread in the central Sierra Nevada and in northern areas.

Forest researchers are able to identify dead trees based on red, yellow or brown foliage — compared with the healthy green needles that firs and pine trees are meant to have. Some dead trees immediately fall over; others slowly crumble.

From mid-July to early October, researchers assessed nearly 40 million acres of land across California. Douglas fir trees saw the biggest spike in mortality rates compared with previous years. An estimated 3 million Douglas firs died, across 190,000 acres, in 2022 — a massive increase of 1,650 percent compared with 2021.

There were nearly 13 million dead white firs across 1.5 million acres, an increase of 691 percent, and more than 15 million red fir trees died across less than a million acres, an increase of 242 percent.

When trees endure long droughts, it makes it hard for them to fight off beetles, maintain their health or recover from adversity, according to Susie Kocher, a forestry adviser at the University of California’s center for agriculture and natural resources.

For Kocher, a registered professional forester, the results aren’t shocking. She witnessed the tree die-off firsthand near her home in the Lake Tahoe Basin. Her neighborhood is dotted with trees stained with red needles — a signal the trees have died.

“It’s not a surprise that drought leads to dead trees,” Kocher said. “Any person looking out their window as they’re driving [near the Lake Tahoe Basin] can see the tree die-off right there. Specifically, I see it all around where I live in the forest.”

It’s hard to keep count of the number of wilting trees when she drives through the basin because “there are too many,” she said.

The new survey paints a picture of severe tree loss in the area surrounding the Lake Tahoe Basin. The Tahoe National Forest saw the highest loss out of all of the state’s national parks with 5 million dead trees across 260,000 acres.

Drought conditions are the main driver of tree mortality. At the end of the summer, 94 percent of the state was experiencing severe or worse drought conditions, according to the U.S. Drought Monitor. The conditions contributed to festering tree diseases and insect outbreaks on drought-stressed trees.

Insects themselves were a major problem. The survey found that Douglas-fir tussock moths, caterpillars that feed on the needles of Douglas fir and spruce trees, were one of the leading causes of death after drought. The caterpillars chew on tree needles, feeding on the foliage and leaving raw exposed twigs, to the point that they are more susceptible to bark beetles and other diseases. Wood-boring beetles killed nearly 400,000 trees across 40,000 acres. Pine beetles contributed to 11 percent of tree decay.

The survey also found that Cytospora canker, a deadly tree fungus that infects trees stressed by insect feeding and drought, was another major reason behind tree death.

Still, this isn’t the worst tree die-off California has seen. Between 2010 and 2016, during years of historically intense drought, the Forest Service counted an estimated 102 million trees dead — 62 million trees died in 2016 alone.

Oppressive drought conditions played a “grim reaper” role between 2020 and 2022, carving through trees that had avoided large-scale die-off and forest fires from 2012 through 2015, said John Abatzoglou, a professor of climatology at the University of California at Merced.

The lingering toll of drought will continue to drive tree deaths in the years to come.

“There is this realization that our forests today will look different in the future,” Abatzoglou said. “There is probably going to be some continued die-off, even though it’s been wet this year. The trees are already sort of going.”

More dead trees may mean more fuel for the next round of forest fires in California, Kocher warns. Dead trees allow for wildfires to spread quicker during dry, blazing conditions, and she suggested removing the decayed timber from the landscape as a preventive measure.

Last year, the state saw record-setting dryness and more than 360,000 acres of earth scorched by wildfire. The Mosquito Fire, which burned more than 76,000 acres of land and killed two people, was the largest wildfire in California last year. Flames from the Mosquito Fire unleashed volcano-like plumes in the skies around northern California.

Reducing the number of trees in areas not severely affected by droughts could reduce forest density and allow individual trees to have access to more moisture and soil.

“In areas where we haven’t had big die-offs, it’s really important to thin the live trees out,” Kocher said, “and in areas where we have had die-offs, it’s important to take the dead trees out so they don’t contribute so much to future fires.”

California is not the only state struggling with tree mortality. In Texas, record heat and drought, which caused 99 percent of the state to experience drought conditions, also weakened trees this summer. Last week, when ice storms hit some of these same areas, thousands of trees collapsed.