Spatiotemporal Relationships between Climate and Whitebark Pine Mortality in the Greater Yellowstone Ecosystem
Whitebark pine (Pinus albicaulis) serves as a subalpine keystone species by regulating snowmelt runoff, reducing soil erosion, facilitating the growth of other plants, and providing food for wildlife. Mountain pine beetle (Dendroctonus ponderosae) is an ideal bioindicator of climate change, because its life cycle is temperature-dependent. Western North America is currently experiencing the largest outbreak of mountain pine beetle on record, and evidence suggests that a changing climate has accelerated the life cycle of this bark beetle. This study explored the relationships between climate, mountain pine beetles, and whitebark pine mortality in the Greater Yellowstone Ecosystem. A time series of Landsat satellite imagery (nine images) was used to monitor whitebark pine mortality in the Greater Yellowstone Ecosystem from 1999 to 2008. The patterns of mortality were analyzed with respect to monthly climate variations over the 9-year period. The impacts of topography and autocorrelation (both spatial and temporal) were also analyzed. The most important predictor variables were autocorrelation terms, indicating a strong host-tree depletion effect. Both drier and warmer climatic conditions favored increased whitebark pine mortality. These results show for the first time a statistical link between climate variability and whitebark pine mortality, probably mediated by mountain pine beetles.
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