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The Cost of Environmental Degradation
Estimating the share of degraded land in total cropping area. FAO (2000) estimates the share of degraded land in total cropping area based on the analysis of the Global Assessment of Soil Degradation (GLASOD) survey data (Oldeman, Hakkeling, and Sombroek 1990; Oldeman 1994). The GLASOD survey establishes a set of geographical areas (mapping units) that are relatively homogeneous in their physical characteristics. Four degrees of land degradation are distinguished in terms of reduction in land productivity: • Light, expressed through a low reduction in productivity • Moderate, expressed through a considerable reduction in productivity • Strong, when biological functions of soil are considerably destroyed and there is no potential for rehabilitation and use • Extreme, when biological functions of soil are considerably destroyed and lands cannot recover In addition, the spatial extent of land degradation reflects the share of degraded land in one geographical area (mapping unit). This share is classified within the following five ranges: 0–5 percent, 5–10 percent, 10–25 percent, 25–50 percent, and 50–100 percent. Twenty combinations of degree and spatial extent of degradation are therefore possible. Those combinations fall within four classes of degradation severity: light, moderate, severe, and very severe. Figure 5.1 shows, for example, that a severely degraded area can mean that (a) 10–25 percent of land is subject to strong degradation; (b) 25–50 percent of land is subject to moderate degradation; or (c) 50–100 percent is subject to Figure 5.1
Classes of Land Degradation Severity spatial extent of degradation (% of mapping unit affected)
degree of degradation
0–5
5–10
10–25 25–50 50–100
light
light
moderate
moderate
strong
severe
extreme
very severe
Source: FAO 2000. Note: The class of degradation severity (light, moderate, severe, or very severe)—as indicated by the shaded areas and keys to the right of the figure—is determined by a combination of the degree and spatial extent of land degradation as defined by the GLASOD survey data.