The Incipient Threat of Land Degradation

Human needs often change the natural system from one that is stable and virtually closed to one that is degrading and more or less open. Failure to rest the land adequately diminishes the productivity of the system gradually, attributable in large part to the loss of nutrients from the system. Though methods to assess land degradation on a large scale are deficient, there is growing concern that degradation of agricultural soil resources - that is, a decline in long-term productive potential- is already seriously limiting production and diminishing ecosystem services in the developing world. This paper reviews our knowledge on the extent of soil degradation to date and the immediate and proximate causes. It discusses a remote-sensing based approach to assessing the decline in land productivity, exemplified for sub-Saharan Africa, which also relates degradation to the ecological and social contexts in which it occurs. Examples are given of the leading causes of soil degradation in that region and the difficulties of eliminating or countering them. Monitoring the health of our soils is urgently needed and will require a long-term commitment, a dense network of monitoring sites and well functioning laboratory facilities. It will require the development of indicators, threshold limits or symptoms that can predict the onset of land degradation. If combined with the use of satellite imagery as discussed in this paper, such a system may be made cost-effective.