In California, there has been a dramatic increase in tree deaths during the 2012-2016 drought, with an estimated 170 million trees dying between 2010 and 2021. This is mainly due to outbreaks of drought and insect infestations. The U.S. Forest Service has detected over 147 million dead trees in California between 2010 and 2018, with the hardest-hit areas in the southern Sierra Nevada Range. The total number of dead trees in California's forests since 2010 is estimated to be over 163 million. These deaths have been primarily caused by bark beetles, and there may be even more trees that have not been counted. Outbreaks of insects can lead to the death of both healthy and already weakened trees.