Forest ThreatNet

Volume 10, Issue 3 - July/August 2016

Western Threat Center Highlight: Bark Beetle Forecast Aims to Predict Risk of Tree Loss in California

A map shows a forecast of bark beetle-caused mortality for CaliforniaLarge parts of California are currently experiencing dramatic levels of tree loss due to a combination of drought and bark beetles. U.S. Forest Service Forest Health Protection staff conduct aerial surveys to collect data and map the extent and severity of tree mortality, which are compiled and finalized across the summer months. To help land managers anticipate the risk of tree loss ahead of these surveys, the Western Threat Center is supporting a project to forecast the intensity and location of bark beetle mortality. Center Director Nancy Grulke and colleagues Zachary Heath (Pacific Northwest Region Forest Health Protection), Haiganoush Preisler (Pacific Southwest Research Station), and Sheri Smith (Pacific Southwest Region Forest Health Protection) analyzed historical aerial survey data and weather variables known to influence bark beetle success, such as precipitation, in order to develop 2015 and 2016 bark beetle forecasts six months before completion of the aerial surveys. Comparison of the 2015 forecast with the 2015 survey data showed only 2% of the forecast fell outside the expected range of mortality. The bark beetle forecast is assisting CalFire, which has used the forecast as a warning system for increased fire risk, and Forest Service managers in the Pacific Southwest Region, who have used the forecast to identify areas in need of spot treatment. Researchers have developed the bark beetle forecast for 2017, and plan to expand the forecast area to include the Pacific Northwest Region.

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Pictured: A map shows the 2016 forecast of bark beetle-caused mortality for California. Warmer colors indicate higher risk of tree loss from bark beetles. Click to enlarge.

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