Land Ecological Changes and Evolutional Patterns in the Source Regions of the Yangtze and Yellow Rivers in Recent 15 Years
近15年来长江黄河源区的土地覆被变化

Based on land ecological classification in the source regions of the Yangtze and Yellow rivers and field investigation, the two phases of TM remote sensing data obtained in 1986 and 2000 were compared. From spatial distribution pattern variations and type transformation trend, the spatial changes and evolutional patterns of land ecosystem in the source regions of the two rivers were analyzed in this paper using the analytical method of landscape ecological spatial patterns. Results show that high-frigid grasslands degraded obviously by 15.82% and 5.15% for cold steppe and cold meadow areas respectively, and high-frigid swamp meadow area decreased by 24.36%. Lake water area was reduced by 7.5%, especially the lakes in the source region of the Yangtze River. Land desertification is developing rapidly and desertified land area has increased by 17.11% on an average.Desertified land in the source region of the Yellow River is expanding at an annual rate of 1.83%. Analysis of the evolutional pattern of land ecotypes shows that the general tendencies of spatial evolution in the regions are coverage reduction and desertification of high-frigid steppe, cover reduction and steppification of high-frigid meadows, and desiccation of swamp meadow. As a result, land ecological spatial distribution pattern in the region has changed and eco-environment is continually worsening.