Print PageRapid and large-scale forest mortality associated with recent climate change and climate-change induced insect outbreaks has been observed over western North America (NA). Climate models project an increase in future temperatures and changes in precipitation for this region. However, quantitative assessments of the magnitude and timing of potential climate-driven changes in vegetation mortality are lacking. We use an Earth System Model (the Community Earth System Model) coupled with a dynamic vegetation model (DGVM) to assess future potential changes in vegetation distributions over western NA under the future A2 emissions scenario. In order to better span uncertainties in future climate, eight different sea surface temperature (SST) projections provided by CMIP3 (phase 3 of the Coupled Model Intercomparison Project) are employed as boundary conditions.
Results/Conclusions
Although all ensemble members project different future climates, there is a broad consensus amongst our simulations that needleleaf evergreen tree coverage is projected to decline by approximately 23% (from 45% to 22%) coincident with a 19% (from 14% to 33%) increase in shrubs and grasses by the end of the 21st century over western NA, mostly occurring over the latter half of the 21st century. The net impact is a 5.8 GtC or about 50% decrease in projected ecosystem carbon storage in this region. Our findings suggest that there is a potential for a shift of tree-covered landscape to shrub and grass-dominated landscapes in western NA due to future warming and consequent increases in water deficits, highlighting the need for improved understanding of mortality mechanisms and the incorporation of these mechanisms into dynamic vegetation models.
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