Doyle Rice

USA TODAY

California is a tinderbox of dead trees, which is fueling the fire risk in the state. According to a report released Wednesday, 26 million trees have died in the southern Sierra Nevada since October 2015.

The deaths are in addition to the 40 million trees that died across the state from 2010 to October 2015, bringing the total to at least 66 million dead trees.

The report, which was prepared by the U.S. Forest Service, was released as several wildfires continue to char thousands of acres across the state, with thousands of Californians ordered to flee their homes.

Four straight years of severe drought in California, a dramatic rise in bark beetle infestation and warmer temperatures are leading to historic levels of tree die-off, according to the report.

According to the forest service, only 77,000 trees have been felled.

"Tree dies-offs of this magnitude are unprecedented and increase the risk of catastrophic wildfires that puts property and lives at risk," said U.S. Department of Agriculture Secretary Tom Vilsack in a statement. The forest service is part of the Agriculture Department.

A 2014 study from the forest service said there were an estimated 11 billion live trees on forest land in the entire state of California.

"While the fire risk is currently the most extreme in California because of the tree mortality, forests across the country are at risk of wildfire and urgently need restoration requiring a massive effort to remove this tinder and improve their health," Vilsack said.