mesoxeric or xeric forbs and xeric bunchgrasses replace the mesic forbs, forming the typical steppe. Dry steppe, lacking in forbs and abundant in xeric bunch-grasses and short semishrubs, occupies the lower reaches where topography and precipitation are even lower and temperature is higher. The major formations in this area include Filifolium sibiricum, Stipa baicalensis, Festuca dahurica, Aneurolepidium chinense, S. grandis, S. krylovii, and Artemisia frigida. In addition to the zonal steppe vegetation, some nonzonal plant communities, including sandy vegetation (sandy sparse woods, sandy shrublands, and sandy semishrublands) and wet lowland vegetation, are also found here.
Since 1949, the Inner Mongolia grasslands have gone through five periods of human utilization and resource management (Yong, 1984). Although there are few reliable statistics for livestock during the pre-1949 era, Yong (1984) indicates that from 1949 to 1958, animal husbandry developed rapidly, and grassland resources were effectively utilized. Domestic livestock, although still small in number, may have increased by 10% per year. During the second period, 1959–1962, because of severe economic difficulties and food shortages, vast areas of the grasslands were put under cultivation. In the economic recovery and readjustment of 1963–1965, animal husbandry in Inner Mongolia developed further. The total livestock in this area increased to a historic peak of nearly 12 million head. As the problem of overgrazing emerged, government agencies began to recognize the need for research into and reconstruction of the grasslands. It was at this time that China's first grassland research center was established in Inner Mongolia. Meanwhile, the Academia Sinica's Integrated Expedition in Inner Mongolia and Ningxia carried out extensive field investigation on regional vegetation, which laid the foundation for subsequent grassland research.
During the Cultural Revolution, from 1966 to 1976, the animal husbandry and environment of the Inner Mongolian grasslands were seriously damaged. This period was marked by the second major expansion of agriculture into the grasslands. Under the pressure of policies to ''make grain production the key link,'' some herdsmen turned from animal husbandry to farming. The large-scale transformation of grasslands into farmlands devastated steppe vegetation and caused large-scale desertification and salinization. The grasslands were degraded, and grassland research and technology were retarded. After the end of the Cultural Revolution in 1976, new policies were announced to protect grasslands and promote animal husbandry. As a result, livestock raising again rapidly advanced. By 1980 the total number of livestock in the Inner Mongolia Autonomous Region reached 40 million.
Prior to the 1950s, agriculture had never been practiced in the Xilin River Basin (Li et al., 1988). Farming on the Baiyinxile State Farm began in 1956, when 9.33 km2 were put under cultivation. The sown area increased to 24.67