Geographically variable response of Dendroctonus ponderosae to winter warming in the western United States



Milder winters have contributed to recent outbreaks of Dendroctonus ponderosae in Canada, but have not been evaluated as a factor permitting concurrent outbreaks across its large range (ca.1500 × 1500 km) in the western United States (US).


We examined the trend in minimum air temperatures in D. ponderosae habitats across the western US and assessed whether warming winters explained the occurrence of outbreaks using physiological and population models.


We used climate data to analyze the history of minimum air temperatures and reconstruct physiological effects of cold on D. ponderosae. We evaluated relations between winter temperatures and beetle abundance using aerial detection survey data.


Extreme winter temperatures have warmed by about 4 °C since 1960 across the western US. At the broadest scale, D. ponderosae population dynamics between 1997 and 2010 were unrelated to variation in minimum temperatures, but relations between cold and D. ponderosae dynamics varied among regions. In the 11 coldest ecoregions, lethal winter temperatures have become less frequent since the 1980s and beetle-caused tree mortality increased—consistent with the climatic release hypothesis. However, in the 12 warmer regions, recent epidemics cannot be attributed to warming winters because earlier winters were not cold enough to kill D. ponderosae.


There has been pronounced warming of winter temperatures throughout the western US, and this has reduced previous constraints on D. ponderosae abundance in some regions. However, other considerations are necessary to understand the broad extent of recent D. ponderosae epidemics in the western US.

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We thank Jim Vandygriff for querying damage data from the main ADS database and Jacques Régnière for the BioSIM temperature database. Helpful comments were provided from Sandy Liebhold. Funding was provided by a cooperative agreement with the Southern Research Station (USDA Forest Service) to M.P.A.

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Weed, A.S., Bentz, B.J., Ayres, M.P. et al. Geographically variable response of Dendroctonus ponderosae to winter warming in the western United States. Landscape Ecol 30, 1075–1093 (2015).

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  • Climate change
  • Demography
  • Mountain pine beetle
  • Process-based model
  • Bark beetles
  • Pinus
  • Cold tolerance