アメリカにおける砂漠化の背景と環境管理

抄録

The United States of America has suffered from the land degradation or desertification in and around semi-arid regions. This paper illustrates the background of desertification, soil erosion and land degradation due to overcultivation and overgrazing, in the U. S. A., mainly in the Great Plains. Measures to soil erosion and overgrazing and environmental management are also discussed. Table 1 summarizes the events related to desertification and environmental management in the United States chronologically.
In protecting non-federal lands and land resources, Soil Conservation Service of U. S. D. A. and the local conservation districts are playing important roles. Soil erosion from croplands is very serious (Fig. 1 and Table 2). The land management in private farms depends much more on the national and international economy. Wars and exports of grains usually brought big profits to farmers, which was an incentive to expand the cropland, and then severe erosion occurred.
The Food Security Act of 1986 includes the soil conservation provisions, which for the first time deny the subsidies to farmers who do nothing to control the soil erosion.
Before Federal Land Policy and Management Act of 1976 was enacted, the federal land had not necessarily been managed well, though the Taylor Grazing Act of 1934 played the significant roles in improving the rangeland conditions, which had been degraded in the late 19th century. After 1976, the improvement of rangeland conditions in federal land goes toward (Table 3) and the management policy is still developing.
Compared with the desertification in developing countries, that in the United States would be caused more by the social and/or economical situations of the nation and the world, under the relatively fragile natural conditions.