ECOSYSTEM PERFORMANCE MODELS FOR FIVE RANGELAND TYPES AND CLIMATE CHANGE IMPACTS ON BIG SAGEBRUSH (ARTEMESIA TRIDENTATA) SUSTAINABILITY IN THE OWYHEE UPLANDS, USA

The introduction of annual grasses and noxious weeds since settlement and increasing fire frequency and severity have had grave ecological consequences for the Great Basin, including the Owyhee Uplands. In this study, we used regression tree models that incorporate interannual weather variations to predict ecosystem performance (growing season Normalized Difference Vegetation Index—NDVI) of five rangeland types. Unlike many greenness studies, our technique separated weather variations from management and disturbance impacts. By comparing the modeled ecosystem performance maps (2000 to 2008) with the actual growing season NDVI for each rangeland type, we identified performance anomalies, or areas that were more or less productive than expected. The results were validated with information on the percentage of bare ground and the stocking rate. We located persistent anomalies from these annual maps and created a map to identify areas trending toward degraded states. We used historical weather data from 1950 and 1970 and future trends climate data for 2040 to assess the sustainability of the Big Sagebrush (Artemesia tridentata) community, a critical habitat for this region. We currently use this method to analyze ecological consequences of a potential land conversion from marginal cultivated cropland to grassland for biofuels production in the Greater Platte River Basin area.