Abstract
Destructive land use is driving long-term losses of ecosystem function and productivity. Satellite measurements of Normalized Difference Vegetation Index (NDVI) since 1981 provide a global yardstick, revealing that a quarter of the land surface has been degrading over the last quarter of a century; every continent and biome is affected with Africa south of the equator, southeast (SE) Asia and south (S) China hardest hit. The loss of primary productivity is equivalent to more than a billion Mg C but the associated emissions from loss of biomass and soil organic carbon are much greater. Degradation is not confined to farmland (18 % of the degrading area is cropland; 47 % is classed as forest); neither is it strongly associated with drylands, population pressure or poverty. A case study using more detailed data for China explores the effects of soil resilience and the association between land degradation and land use. NDVI can only be a proxy measure of land degradation; assessment of ecosystem services is a further step removed. Remotely-sensed data can be used along with climatic and topographic data as an input to models that predict the provision of these services but the processes, drivers and effects beyond NPP are unseen and more importantly, unmeasured. This is an issue for emerging markets in environmental services.
Bai, Zhanguo