Land degradation in the drylands, also called desertification, has affected the world for centuries, even millennia, in Africa, Asia, and Mediterranean Europe, for one or two centuries in the Americas, and 100 years or less in Australia. Among the principal degradation processes are vegetation degradation in rangelands, water and wind erosion, salinization of irrigated and certain semiarid lands, and soil compaction. Farmers, ranchers, and researchers, in general, are aware, from their personal experiences, of the environmental changes land degradation has brought. Unfortunately, there are little good research data on just how much damage has been done. Much of the evidence is from what can be seen, such as gullies, mobile sand dunes, and buried cities, as well as undocumented anecdotes of ancient and modern travelers. Given the uncertain data base, it is no wonder that there are radically different beliefs of the severity and the damage cost of land degradation in the drylands. This review attempts to analyze global information sources and draw tentative conclusions on the significance of on-site and off-site impacts of land degradation. The pressing need is for more reliable data that will help determine the priority the problem should have in national and international planning.
