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Spruce beetle outbreak was not driven by drought stress: evidence from a tree-ring iso-demographic approach indicate temperatures were more important
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  • Jessika Pettit,
  • Steve Voelker,
  • R. Justin DeRose,
  • Julia Burton
Jessika Pettit
Czech University of Life Sciences Prague
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Steve Voelker
State University of New York College of Environmental Science and Forestry at Syracuse
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R. Justin DeRose
Utah State University
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Julia Burton
State University of New York College of Environmental Science and Forestry at Syracuse
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Abstract

Climate change has amplified eruptive bark beetle outbreaks over recent decades. However, for projecting future bark beetle dynamics there is a critical lack of evidence to differentiate how outbreaks have been promoted by direct effects of warmer temperatures on beetle life cycles vs indirect effects of drought on host susceptibility. To diagnose whether drought-induced host-weakening was important to beetle attack success we used tree death date demography during a spruce beetle outbreak to differentiate early and late-dying trees and then determined whether early-dying trees had greater sensitivity of tree-ring carbon isotope discrimination to drought. Drought-sensitivity did not differ among early- vs late-dying trees, suggesting proposed links between spruce beetle outbreaks and drought primarily reflect warming- amplified beetle life cycles rather than drought-weakened host defenses. Additional iso-demographic studies are needed to diagnose the role of direct vs indirect climate effects across wider regions and other species.