cover degradation include (1) increase in the area of soils transformed by what the Chinese call "sandization" [sha-hua]; (2) deterioration of the physical properties of soil components, such as the loss of soil structure and the decline of soil water status; (3) decline of soil fertility and organic matter; (4) overall increase in the area of salinization and swamping; and (5) intensification of soil erosion. Li notes that natural environmental changes, socioeconomic development, and human activities are all major causes of soil cover degradation, with human activity being the most important.

According to Li, degradation of the grass cover is the most important cause of soil degradation in natural grasslands. Overgrazing and trampling by livestock are the main reasons for the loss of grass cover. The construction of roads, increasing access throughout the grasslands, is another factor. Li reports that all these phenomena can be seen clearly on Landsat Multispectral Scanner (MSS) imagery. Because of grassland degradation, organic matter in the soil decreases, soil structure changes, compaction occurs, and salinization and swamping develop.

Li concludes that it is important to use satellite remote sensing to monitor grassland resources, land use, and other dynamic changes of soil cover and structure. By establishing a correlation model that relates climate factors, soil moisture, and grassland biomass, and combining the model with remotely sensed images of vegetation growth, one can predict the biomass of various grassland types and use these projections for scientific management.

Shi Peijun of Beijing Normal University and his colleagues at Inner Mongolia University (1990) have investigated soil erosion problems of grasslands in Inner Mongolia, using both ground and remote sensing methods. This work was carried out in three steps: (1) analysis of information from ground investigations; (2) construction of indices of soil erosion from visual interpretation of remotely sensed images; and (3) relating the information from steps 1 and 2. Shi et al. (1990) classify soil erosion as shown in Table 3-2. "Class 3" erosion—2500–5000 tons/km2 per year—would be considered serious by U.S. standards (i.e., 4–7 tons per acre per year). Table 3-3, which shows areas affected