Soil Vulnerability to Future Climate in the Southwestern USA, with Implications for Vegetation Change and Water Cycle.

 

                The recent drought (1999-2009) in the southwestern US caused rapid, regional-scale mortality of dominant pinyon pines (Pinus edulis) from infestations of bark beetles (Ips confusus) associated with extreme drought stress. The recent drought affected all age classes even at high elevations. Tree mortality as a result of direct or indirect impacts of climate has been included in vegetation models using various approaches. Empirical mechanistic (process-based) models include species-specific parameters with temperature and soil moisture thresholds based on published empirical information on those species physiological constraints. The “average” response to climate-driven stress (heat, cold, flood, drought) can be used as a coarse scale indication of potential die-off when under certain climate conditions and given a set of soil constraints, one vegetation type gets replaced by a better adapted type.  In all cases, these modeling approaches assume that soil characteristics for the area of concern have been measured and mapped appropriately and that the simulation of the hydrological cycle associated with the ecosystem is dependable.  This project aggregates and synthesizes all available regional soil information to create a soil vulnerability index that captures our understanding of the region’s vulnerability to climate change though its soil characteristics and  compares hindcasts of vegetation die-offs to this index to test the model’s skill at simulating the impacts of past droughts (1950s, 2000s). We will generate improved input datasets required to run the climate change impact models and identify gaps in our knowledge base in order to focus future field sampling efforts in areas of greatest need. Using these improved soils datasets, we will simulate future vegetation die-offs using a variety of future climate scenarios and speculate on future soil vulnerability due to the change in vegetation cover.