Mapping land degradation by comparison of vegetation production to spatially derived estimates of potential production

There is an urgent need for quantitative methods by which actual, as opposed to potential degradation can be mapped using spatially consistent criteria for large regions. This study tested the Local NPP Scaling (LNS) method, where the growth season sum NDVI (ΣNDVI), a surrogate for productivity, of each pixel was expressed relative to the highest values (90th percentile) of ΣNDVI observed in all pixels falling within the same land capability unit (LCU). The objective of this study was to determine if the LNS approach can be used to map degraded areas: (i) by determining if areas with low LNS values co-occur with degraded areas mapped with Landsat TM and (ii) testing the persistence of these areas over multiple years. Most of the areas with low LNS values did coincide with degraded areas, with the exception of four LCUs, which either contained steep precipitation gradients or landscape variability, which probably obscured the human impacts. The performance of the LNS method is therefore largely determined by the level of detail of the stratification data (e.g. LCUs) used. The conclusion is that the LNS method is a valuable tool for mapping land degradation at a regional scale.