ABSTRACT
DESERTIFICATION AND LAND DEGRADATION, DRYLANDS AND NON-DRYLANDS
The decline in biological productivity of economic value is driven by biophysical processes of “land degradation,” which can operate on lands used by people anywhere on earth, but mostly affect lands whose productivity is constrained by water. Water is one of the raw materials required for the biological production process, but atmospheric CO2 and soil minerals, as well as light are required too. Each of these can limit productivity, even if all the others are
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available in abundance. Land degradation occurs in areas of low water and high evaporation, thus making soil water the limiting factor. This water scarcity exists in all lands exposed to a potential annual evaporative loss that is at least about one and one-half times greater than the mean annual gain through rainfall. These are “drylands,” and depending on their degree of aridity, they are classifi ed into desert drylands (hyper arid and arid drylands) and non-desert ones (semiarid and dry subhumid drylands) (Fig. 1).
