How many millions?  Try 66 million dead trees!  A number hard to visualize! Bark beetles, heat and drought have killed over 66 million trees in the Sierra Nevada forests since 2010

Wildfires are part of the California landscape but this year the drought, extreme heat and high winds have fueled fires all over the west. But another more ominous enemy is driving California’s destructive blazes this fire season: tens of millions of dead trees. The death rate of these trees has increased rapidly within recent months, with 26 million trees dying in and around the Sierra Nevada forests since October 2015.

Across California, more than 4,900 firefighters were battling seven large wildfires early this week. Other larger wildfires in the state so far this season haven’t been fueled by these dry, dead trees, since they have occurred at lower elevations. The tree mortality becomes a factor at 3,000 feet of elevation. In some of these areas, 85% to 95% of the trees are dead and highly flammable. These dead trees are significantly drier and are vastly more flammable than ones that are still alive. Pairing dry, dead trees with a fire and windy conditions makes for a worst-case scenario.

As the trees in California grow weaker due to lack of water, they are unable to battle an increased population of bark beetles, which infest and eat away at the trees. So far, only 77,000 dead trees have been removed from the Sierra, Sequoia and Stanislaus national forests, according to the U.S. Forest Service. Just a few million left to go.