Simulated vegetation responses to potential future climate change in western North America

Background/Question/Methods

Understanding how potential future climate changes may affect vegetation is important for developing adaptive management plans for responding to climate change. This study used LPJ, a dynamic global vegetation model, to simulate the potential responses of vegetation to future climate change for a study area encompassing the northwestern United States and southwestern Canada. We used simulations of potential future climate from the coupled atmosphere-ocean general circulation models CCSM3, CGCM3.1(T47), GISS-ER, MIROC3.2(medres), and UKMO-HadCM3 produced using the A1B and A2 greenhouse gases emissions scenarios. Data for each climate simulation were obtained from the World Climate Research Programme’s (WCRP’s) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset. The future climate data were downscaled to a 30-arc-second grid of the study area by calculating, interpolating, and applying future climate anomalies to CRU TS2.1 (1961-1990 30-year mean) climate data interpolated to the same grid. LPJ was run using these climate data and parameterized to simulate 10 plant functional types, which were aggregated into basic habitat types (e.g., forest, grassland). The simulated vegetation changes for 2070-2099 (30-year mean) were evaluated across the study area and for individual ecoregions, using The Nature Conservancy’s ecoregional classification.

Results/Conclusions

Simulated vegetation responses to potential future climate change varied across the study area. Certain ecoregions showed relatively little projected future changes in vegetation for 2070-2099 (30-year mean), such as the Pacific Northwest Coast ecoregion, which was simulated to remain forested under future climate conditions. In contrast, woody vegetation was simulated to expand by 2070-2099 (30-year mean) in more xeric regions of the study area, such as parts of the Columbia Plateau ecoregion, and this simulated expansion agrees with the results of previous modeling studies for the region. In addition to ecoregional changes, certain vegetation changes occurred throughout the study region, such as the simulated reduction in subalpine habitat. These results provide information on the spatial dynamics of potential vegetation responses as well as the potential sensitivity of particular vegetation types and ecoregions in the study area to future climate changes. We also describe some of the limitations and uncertainties associated with the simulated climate and vegetation data that must be considered when interpreting the study results and using the results for management applications.