To date in 2020, 1,217 wildfires have burned 1,473,522 million acres of National Forest System lands in California; 8,486 wildfires have burned over 4 million acres across all jurisdictions in California. This current fire activity comes after forests in the region experienced an extreme drought accompanied by warmer than normal temperatures from 2012 to 2015, resulting in the deaths of over 147 million trees, mostly from bark beetles. These dead trees are now adding more fuel to this summer's wildfires, especially in the southern and central Sierra Nevada, where tree mortality was the heaviest.
source https://phys.org/news/2020-10-thinning-treatments-tree-mortality.html