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SPUR2 is a general grassland ecosystem model that simulates carbon and nitrogen cycling through aboveground live and dead vegetation, live and dead roots, litter, and soil organic matter.  Effect of stocking rate, season of grazing, and type of grazing system have been incorporated into the model.  SPUR2 has been modified to simulate the direct effects of CO₂ on plant production.  A user interface has been developed to assist with model parameterization.  The model is driven by daily inputs of precipitation, maximum and minimum temperatures, solar radiation, and daily wind run.  These variables are derived either from existing weather records or from use of a stochastic weather generator.  The hydrology component calculates upland surface run-off volumes, peak flow, snow melt, upland sediment yield, and channel stream flow and sediment yield.  Soil-water tensions, used to control various aspects of plant growth, are generated using a soil-water balance equation.  Surface run-off is estimated by the SCS curve number procedure and soil loss is computed by the modified universal soil loss equation.  The mechanistic process-oriented structure of SPUR2 makes the model well suited for examining the interactions between management decisions and climatic influences on short-term ecological processes and evaluating possible adaptive management strategies.

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