USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Tree Mortality

Predictor map forecasts reduced likelihood of tree mortality in 2018

Image of a publication titled, 'When the well runs dry.'
Download the publication "When the Well Runs Dry" to learn more about factors in the environment that lead to severe bark beetle outbreaks.

For the third consecutive year, PSW and its collaborators have created a map representing the projected number of trees likely to suffer from beetle- or drought-related mortality. Between 3 million to 26 million trees are projected to die in 2018 from drought or beetles, down from 27 million in 2017 and a peak of 62 million in 2016.

The maps are generated by combining aerial survey data with variables known to influence bark beetle-induced tree mortality, such as low precipitation and high beetle pressure (as indicated by high levels of tree mortality in prior years).

The predictor map is a valuable tool for land managers to adapt management strategies or prioritize treatment locations to coincide with areas most likely to experience mortality within the next two years.

Understanding Forest Ecology: Fire, Water, and Bark Beetles

An estimated 129 million trees have died in California’s national forests since 2010.  In this video, researchers discuss two things that help influence forest growth and survivorship: fire and water. Water influences the size and type of trees, as well as a forest’s density. Fire controls what happens in the understory—the future of the forest.

PSW recently contributed to the article "Observed and Anticipated Impacts of Drought on Forest Insects and Diseases in the United States," published in the May 2016 issue of Forest Ecology and Management. It helps provide an understanding of the relationship between drought and bark beetles.

When forest density is high under drought conditions, competition for water is amplified. Trees in this weakened state are less effective at defending themselves from bark beetles and other pests.

Each successful onslaught from the beetles brings forth a new brood of thousands more, further compounding the problem. As the number of host trees dwindle and precipitation returns, conditions become less favorable for the beetles and balance in the forest is restored.

Additional Resources
Last Modified: Jun 4, 2018 01:34:31 PM