From the joint state and federal California Tree Mortality Task Force:
More the California Department of Forestry and Fire Protection:
According to the U.S. Forest Service, tree mortality from bark beetles and drought has reached over 29 million trees, up from 3.3 million trees in 2014. Most tree mortality in California has occurred in the southern Sierra Nevada and the Central Coast. Researchers at the Carnegie Institution for Science have learned that approximately 58 million additional large trees are suffering from severe canopy water losses.
Ponderosa pine, Jeffrey pine, and pinyon pines are most impacted by bark beetles, but many trees have died just from lack of water in the current drought. Most other pine species, white fir and incense-cedar are also heavily impacted by the prolonged drought and by bark beetles. There is also an increase in tree mortality among oaks, although it is primarily attributed to drought, not bark beetles.
Bark beetles are small insects, generally black, hard-shelled and approximately 5 millimeters in length—about the size of a piece of cooked rice. Bark beetles tunnel under bark, cutting off the tree’s supply of food and water needed to survive. Bark beetles can kill a tree in as little as two to four weeks during warmer months.