Effects of Future Warming and Fire Regime Change on Boreal Soil Organic Horizons and Permafrost Dynamics in Interior Alaska

There is evidence that ongoing climate change is affecting fire frequency, extent, and severity in the interior boreal region of Alaska, and these changes are likely to continue into the future. In this study we couple a landscape fire dynamics model with an ecosystem model in an application to evaluate the long term effects of changes in climate and fire regime on soil organic horizons and permafrost dynamics in interior Alaska. Changes in fire regime were simulated by the Alaska Frame-based Ecosystem Code (ALFRESCO) model driven by downscaled GCM climate outputs from CCCMA-CGCM3.1 and MPI ECHAM5 models using the A1B scenario at 1km x 1 km resolution for the Yukon River Basin in Alaska. The outputs of ALFRESCO were used to drive the dynamic organic soil version of the Terrestrial Ecosystem Model (DOS-TEM). ALFRESCO simulated fire activity would be enhanced through the middle of the 21st Century, after which fire activity would revert to pre-1990 levels because of a shift in forest composition (i.e., fuels) to a greater fraction of deciduous forest. The model framework estimated that the fibrous organic horizon would lose C through the middle of the 21st Century for the warmer ECHAM5 scenario, but would gain C throughout the 21st Century for the CCCMA scenario. The amorphous organic horizon lost C through the 21st Century for both scenarios. The active layer deepened across the basin from about 1 m to between 1.6 and 1.8 m by the middle of the century and then returned to current depth by the end of the 21st Century. These results suggest that it is important to couple changes in the soil organic horizons of boreal ecosystems to permafrost dynamics in order to fully understand the effects of changes in climate and fire regime on regional boreal ecosystem C storage.