Testing a sahelian grassland functioning model against herbage mass measurements

A simple grassland process model is tested against ground measurements collected during 15 years in the sahelian zone in Mali. The model uses standard daily meteorological variables and a limited number of site specific parameters to simulate herbage growth and canopy functioning. The model has two calibration parameters. Due probably to the strong interannual variation of both the herbaceous layer in terms of floristic composition and soil nutrient mineralization, the use of default values for the two calibration parameters leads to large errors in the prediction of herbage yields. In contrast, once the parameters have been optimised, a good concordance is found between the model outputs and the seasonal variation of the herbage standing mass in sites on sandy soils located along a north-south bioclimatic gradient.