Assessment of desertification around deep wells in the Sahel using satellite imagery.
Normalized difference vegetation index measurements from the advanced very high resolution radiometer on the NOAA satellites were used to estimate the total vegetation production during 1987 on transects from 20 deep wells in the N. Ferlo region of Senegal. The herbaceous layer of the open grassland vegetation in most of the region was dominated by fine-leaved annual grasses including Schoenefeldia gracilis, Cenchrus biflorus, Dactyloctenium aegyptium and Aristida mutabilis. Regression analysis indicated no consistent relationship between primary production and proximity to a well at a resolution of 1.1 km. Most of the variance in the data was explained by differing mean productivities at the different wells correlated with a gradient of increasing rainfall southward. Distance effects fitted to model the change in productivity with distance from the wells produced positive and negative slope coeff. which were probably associated with factors other than grazing.