Among Yosemite's emerald forests, parched brown timber poke out like matchsticks waiting for a spark.

There are 2.4 million dead trees within about 131,000 acres of the national park, according the latest fall count, says park spokesperson Scott Gediman.

"As long as these things have been tracked, it's the most dead trees we've seen in the park," Gediman says.

Dead trees can pose a danger to humans; a falling pine killed a Yosemite employee in March. They also can fall on roads, hotels, cabins and tents.

"Our first concern is the health and safety of the park visitors," he says.

What's more, all of this dead foliage is highly flammable, potential fuel for forest fires that burn hotter and faster than those running through a healthy forest.

"With fire, the concern is the increased fuel load," Gediman explains. " The more dead trees, the more fuel for fire to burn."

Tree mortality is a natural part of a healthy forest's life cycle, but in recent years the number of dying trees has been unprecedented as a result of ongoing drought, warming temperatures, poor forest health and native bark beetles.

Dead trees are a problem throughout California; the most recent survey by the U.S. Forest Service found that more than 102 million trees died across 7.7 million acres of the state between 2010 and 2016.

The recent five-year drought is to blame for the bark beetle infestation. This tiny bug the size of a rice grain drills into trees, especially the Sierra's Ponderosa pines, and lays eggs under the bark. When the larvae hatch, they eat the cambium layer that carries the trees' nutrients and inject a fungus that thwarts sap production.

A healthy tree can defend itself from a beetle attack by producing pitch and pushing the bugs out of their holes, but a water-starved one loses the battle.

"The bark beetle is a naturally occurring insect," Gediman says. "They'll go in and kill trees every year, but with more drought, the trees natural defense mechanism breaks down. It's like a human being with a weak immune system."

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Woody Hastings, the renewable energy implementation manager for the Santa Rosa–based Center for Climate Protection, visits Yosemite every spring. In recent years, he has noticed the increasing number of dead brown trees intermixed with seemingly healthy green ones.

"On some of the hillsides in the distance, it almost looked like a forest of autumn trees on the East Coast," Hastings wrote in a blog post for the center.

Hastings says the sight is especially unsettling because it's not like looking at an area of forest where the trees have burned and you think, "Oh, they'll grow back."

"These trees are dying among the healthy trees and it's not going to stop," he told SFGATE.

None of this is surprising to Hastings.

"What we're seeing here through our lens of a global climate is an expected result," he says. "This is the result of drought. If we don't get a lot of rain this year we could shift back into drought conditions. It appears there's a dramatic change underway in the flora."