Tree Mortality
in the Sierra Nevada

The Problem

California is experiencing tree die-off at an unprecedented scale, and the Sierra Nevada Region has been hit extremely hard. 129 million trees have died across the state due to drought and bark beetles since 2010, and 85 percent of those dead trees are in the Sierra.

hillside showing few dead trees

Madera County hillside before tree mortality began spreading. Photo by Margarita Gordus, California Department of Fish and Wildlife.

hillside covered in dead trees

The same Madera County hillside after tree mortality began spreading. Photo by Margarita Gordus, California Department of Fish and Wildlife.

Tree Mortality Progression

Sierra Nevada forests and watersheds are at a critical point. Ongoing drought, a century of fire suppression, widespread tree mortality due to insect attacks and disease, and a changing climate have led to incredible changes across the Sierra Nevada Region. Even though California received record-breaking rains during the winter of 2016-2017, the effects of five consecutive years of drought, an increase in the bark beetle population, and warming temperatures have led to continued die-off.

This animation shows the progression of tree mortality across California from 2006—2017. California experienced a normal amount of background mortality between 2006—2014: less than six trees were killed per acre each year. In 2015 and 2016 mortality increased across California, with a huge spike in the Southern Sierra: well over 36 trees were killed per acre each year.

The Impacts

Millions of dead trees can fuel larger, more damaging wildfires which can have long-term impacts on our water, air, wildlife, recreation, and climate.

The Solution

What is Being Done?

California’s Tree Mortality Task Force (TMTF) is working to address immediate public health and safety risks by removing dead trees from roads, transmission lines, public recreation sites, and communities. The Sierra Nevada Conservancy is a member of the Tree Mortality Task Force and is working closely with other state, local, and federal agencies, utilities, industry representatives, and environmental stakeholders to look for long-term solutions that support healthy forests and communities.

Collectively, the TMTF has removed over one million dead trees in areas where public safety was at highest risk, but with a staggering 129 million dead trees, the work of the task force is far from over.

What Else Can Be Done?

Overgrown forests are more susceptible to insect attack and drought because there are too many trees competing for limited water and nutrients. Reducing competition by doing more restoration, such as ecologically-sound thinning and using prescribed or managed fire, can help protect our still-green forests from future drought, insects, and disease.

Prescribed burning and forest thinning reduces tree mortality by reducing competition between trees and strenghthening their natural defenses against bark beetles

The Sierra Nevada Watershed Improvement Program – a partnership between the Sierra Nevada Conservancy and the U.S. Forest Service – is working to increase the pace and scale of restoration across the Sierra Nevada Region by increasing funding, addressing policy impediments, and increasing infrastructure needed to support restoration.