近30年来长江源区土地覆被变化特征分析

长江源区是我国重要的水源涵养地。本文利用20世纪70年代中后期、90年代初期、2004年和2008年共4期土地覆被数据,通过土地覆被转类途径与幅度、土地覆被状况指数和土地覆被转类指数,分析评价了长江源区近30年来土地覆被与生态状况的时空变化特征。结果表明:草地是长江源区主要的土地覆被类型,2008年草地面积占该区总面积的66.93%。在70年代中后期-90年代初期、90年代初期-2004年和2004-2008年的3个时段内,土地覆被状况指数变化率分别为-0.15、-0.24和0.01;土地覆被转类指数分别为-0.20、-0.66和0.08。近30年来,长江源区土地覆被和生态状况总体经历了变差-显著变差-略有好转的过程。2004-2008年,长江源区年平均温度比前期(70年代中后期-2004年)升高了0.57℃,年平均降水量比前期增加了17.63mm。区域气候变化有助于自然生态系统的恢复。后期生态保护与建设工程的实施,对植被恢复产生了一定的积极作用。

Characteristics of Land Cover Change in Headwaters of the Yangtze River over the Past 30 Years

The water conservation service of headwaters of the Yangtze River is very important for ecological se-curity in China. It is generally acknowledged that the source of the Yangtze River includes the Tuotuohe headwa-ter, Dangqu headwater and Chumaerhe headwater. Based on the land cover dataset of middle and late 1970s, ear-ly 1990s, 2004 and 2008, this paper analyzed temporal and spatial change characteristics of land cover and eco-logical condition in headwaters of the Yangtze River over the past 30 years, using the method of direction and ex- tent of land cover change, land cover condition index and land cover change index. The results showed that grass-land was the main land cover type in this region in 2008, with a ratio of 66.93% in area. The glaciers were main-ly distributed in Tuotuohe headwater, while the marshland was mainly distributed in Dangqu headwater. The change rate of land cover condition index during 1970s-1990s, 1990s-2004 and 2004-2008 was-0.15,-0.24 and 0.01, respectively; while the land cover change index of three periods was -0.20, -0.66 and 0.08, respective- ly. The land cover and ecological condition of the study area had overall experienced a process of degenerated-obviously degenerated-slightly meliorated since 1970s. The mean annual temperature and precipitation from 2004 to 2008 was 0.57℃ and 17.63mm higher than that from 1970s to 2004. Regional climate change over re-cent years was helpful for natural ecosystem recovery. In addition, implementation of the ecological protection and construction project since 2004 also had certain positive effects on vegetation restoration.