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Individual Highlight

Observed and Anticipated Impacts of Drought on Forest Insects and Diseases

Photo of Impacts of drought and insects at Bass Lake Ranger District, Sierra National Forest, May 2016. Christopher J. Fettig, U.S. Department of Agriculture Forest Service.Impacts of drought and insects at Bass Lake Ranger District, Sierra National Forest, May 2016. Christopher J. Fettig, U.S. Department of Agriculture Forest Service.Snapshot : Changes to Earth’s climate are projected to include increases in temperature and changes in precipitation patterns that will increase the frequency and severity of droughts, particularly in the western U.S. Forest Service researchers define the impacts of drought on forest insects and diseases in the U.S. and discuss the role of forest management in mitigation of infestations during drought.

Principal Investigators(s) :
Fettig, Chris 
Research Station : Pacific Southwest Research Station (PSW)
Year : 2016
Highlight ID : 1023

Summary

Current knowledge concerning the effects of drought on forest insects and diseases was reviewed and compared between the moderately wet and structurally diverse forests of the eastern United States and the drier forests of the western United States. Evidence suggests a non-linear relationship between drought intensity and outbreaks of aggressive bark beetle species (i.e., those capable of causing extensive levels of tree mortality) in the western United States, where moderate drought reduces bark beetle population performance and subsequent tree mortality and intense drought increases bark beetle performance and tree mortality. There is little evidence for a role of drought in outbreaks of the southern pine beetle in the southeastern United States. Defoliators show no consistent response to drought. Interactions between forest diseases and drought are poorly understood, but available evidence suggest reduced pathogen performance and host impacts for primary pathogens and pathogens whose lifecycle depends directly on moisture (humidity). In contrast, secondary fungal pathogens are likely to have greater performance and host impacts. The scientists published their results in a special issue on drought in Forest Ecology and Management. A related effort explores the role of drought on recent levels of tree mortality in the Sierra Nevada, where some 67 million trees have died.

Forest Service Partners

External Partners

  • Rocky Mountain Research Station
  • Colorado State University
  • Dartmouth College
  • Northern Arizona University
  • U.S. National Park Service
  • University of Idaho