Warming increased bark beetle-induced tree mortality by 30% during an extreme drought in California

Zachary J Robbins; Chonggang Xu; Brian H Aukema; Polly C Buotte; Rutuja Chitra-Tarak; Christopher J Fettig; Michael L Goulden; Devin W Goodsman; Alexander D Hall; Charles D Koven; Lara M Kueppers; Gavin D Madakumbura; Leif A Mortenson; James A Powell; Robert M Scheller

doi:10.1111/gcb.15927

Warming increased bark beetle-induced tree mortality by 30% during an extreme drought in California

Glob Chang Biol. 2022 Jan;28(2):509-523. doi: 10.1111/gcb.15927. Epub 2021 Oct 28.

Authors

Zachary J Robbins^{1

2}, Chonggang Xu¹, Brian H Aukema³, Polly C Buotte⁴, Rutuja Chitra-Tarak², Christopher J Fettig⁵, Michael L Goulden⁶, Devin W Goodsman⁷, Alexander D Hall⁸, Charles D Koven⁹, Lara M Kueppers⁴, Gavin D Madakumbura⁸, Leif A Mortenson⁵, James A Powell¹⁰, Robert M Scheller²

Affiliations

¹ Earth and Environmental Sciences Division (EES-14), Los Alamos National Laboratory, Los Alamos, New Mexico, USA.
² Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina, USA.
³ Department of Entomology, University of Minnesota, St. Paul, Minnesota, USA.
⁴ Energy and Resources Group, University of California Berkeley, Berkeley, California, USA.
⁵ Pacific Southwest Research Station, USDA Forest Service, Davis, California, USA.
⁶ Department of Earth System Science, University of California, Irvine, California, USA.
⁷ Canadian Forest Service, Natural Resources Canada, Victoria, British Columbia, Canada.
⁸ Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA.
⁹ Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA.
¹⁰ Mathematics and Statistics Department, Utah State University, Logan, Utah, USA.

PMID: 34713535
DOI: 10.1111/gcb.15927

Abstract

Quantifying the responses of forest disturbances to climate warming is critical to our understanding of carbon cycles and energy balances of the Earth system. The impact of warming on bark beetle outbreaks is complex as multiple drivers of these events may respond differently to warming. Using a novel model of bark beetle biology and host tree interactions, we assessed how contemporary warming affected western pine beetle (Dendroctonus brevicomis) populations and mortality of its host, ponderosa pine (Pinus ponderosa), during an extreme drought in the Sierra Nevada, California, United States. When compared with the field data, our model captured the western pine beetle flight timing and rates of ponderosa pine mortality observed during the drought. In assessing the influence of temperature on western pine beetles, we found that contemporary warming increased the development rate of the western pine beetle and decreased the overwinter mortality rate of western pine beetle larvae leading to increased population growth during periods of lowered tree defense. We attribute a 29.9% (95% CI: 29.4%-30.2%) increase in ponderosa pine mortality during drought directly to increases in western pine beetle voltinism (i.e., associated with increased development rates of western pine beetle) and, to a much lesser extent, reductions in overwintering mortality. These findings, along with other studies, suggest each degree (°C) increase in temperature may have increased the number of ponderosa pine killed by upwards of 35%-40% °C^-1 if the effects of compromised tree defenses (15%-20%) and increased western pine beetle populations (20%) are additive. Due to the warming ability to considerably increase mortality through the mechanism of bark beetle populations, models need to consider climate's influence on both host tree stress and the bark beetle population dynamics when determining future levels of tree mortality.

Keywords: bark beetles; climate impacts; drought; forest dynamics; modeling; tree mortality.

MeSH terms

Animals
Coleoptera*
Droughts
Pinus ponderosa
Pinus*
Plant Bark
Trees