California Tree Mortality Numbers Released: 18 Million Trees Died In 2018

  • By Kayanna Warren, Ecologist, Forest Health Monitoring, Pacific Southwest Regional Office
A graph show number of dead trees in California rising. An aerial photo showing brown dead trees spotted throughtout the Sierra Nevada.

The annual Forest Health Aerial Survey* numbers for 2018 were released February, 2019.

While the estimated acreage with tree mortality (2 million) and numbers of dead trees (18 million) in 2018 was down from 2017 (2.5 million and 27 million) and down from the peak years during the 2012-2016 drought, the numbers remained extremely high relative to background mortality rates.

The total number of trees that have died since 2010 across the state is estimated to be 147 million, most of which are concentrated in the southern Sierra Nevada.

In 2018, mortality was highest in white and red fir, which accounted for 75 percent of the observed mortality: 14 million across 1.4 million acres. Mortality increased in 2018 in tanoak and Douglas-fir.

While good precipitation in the winter of 2016-2017 officially ended California’s drought, below-average precipitation the following year slowed the recovery of surviving trees. Additionally, wet seasons are expected to increase levels of fungal activity, e.g. – Sudden Oak Death.

For more information by region of California, downloadable geodatabases, and maps, please visit:

More information about Tree Mortality in California is available on our website at

See also:

*The primary purpose of the aerial survey is to create sketch maps of areas containing current year conifer and hardwood mortality, defoliation, and other damage. USDA Forest Service, Pacific Southwest Region, State and Private Forestry staff conduct annual aerial surveys throughout forested areas of California by recording observations from aircraft. Most national forests and parks in California are surveyed, along with other federal, state, and private forested lands.  Aerial Surveys have been conducted annually since 1994 by Pacific Southwest Region (Region 5) Forest Health Protection staff to assess the current health of California forests.

2014-2017 Tree Mortality Map.

Cumulative tree mortality in California since the onset of the major mortality event in 2014. (Map courtesy of Kayanna Warren)

2018 Tree Mortality Map.

Forest Health Protection Aerial Detection Monitoring 2018 Survey. (Map courtesy of Kayanna Warren)