脆弱和趋于恶化的西部生态 占我国国土面积５０％以上的西部和北部地区，降水量稀少，而且季节分配不均，受到严重缺水的威胁，这是造成西部经济滞后的一个重要根源。近２０年来全球荒漠化面积已占陆地面积的２５％。我国西部荒漠化的土地以每年３００万亩的速度扩大。据估计每 The fragile and deteriorating western ecosystems, which account for more than 50% of China’s total land area, have scarce precipitation and uneven seasonal distribution and are threatened by severe water shortage. This is an important source of stagnation in the western region. In the past 20 years, the global desertification area has accounted for 25% of the land area. The desertified land in western China has been expanding at an annual rate of 300 mu. It is estimated that each