近45年长江黄河源区高寒草地退化特征及成因分析

Rate and causes of degradation of alpine grassland in the source regions of the Yangtze and Yellow Rivers during the last 45 years

根据1969年航片数据、1986,2000,2007年以及2013年TM数据建立的长江黄河源区高寒草地生态系统空间数据集,结合该地区近50年的气候资料以及人类活动状况,分析了长江黄河源区高寒草地生态系统在全球变化背景下的变化趋势及其驱动因素。结果表明,近45年长江黄河源区高寒草地呈现以覆盖度降低、破碎化与干旱化加剧为主的退化趋势,长江黄河源区高寒草地退化的速率在20世纪80年代后期呈迅速增加趋势,2000年后退化速率逐渐降低;气温升高引起的区域的暖干化是导致长江黄河源区高寒草地生态系统退化格局形成的主要原因。过度放牧和人类不合理的开发是导致长江黄河源区高寒草地退化加剧的重要因素。

Alpine grassland is the main vegetation type in the source regions of the Yangtze and Yellow Rivers, and accounts for about 70% of the total area in this region.As a result,maintenance of ecosystem balance,wa-ter cycling and soil-atmosphere exchanges in these regions critically depends on the status of the local alpine grasslands.With current global changes such as climate change,and increased human population in the region, alpine grassland in this region has been subject to increasing grazing pressure with significant changes resul-ting.These environment and regional economic changes have attracted widespread attention.In this research, alpine grassland degradation in the source regions of Yangtze and Yellow Rivers was quantified by analysis of images obtained by aerial photography in 1969 and TM remote sensing data captured in 1989,2000,2007 and 2013.In addition,with the inclusion of climatic observation data and data on human factors,the causes of the degradation were analyzed by principal component analysis and the gray correlation method.The results show that the alpine grassland degradation is characterized by reducing coverage,and increasing fragmentation and desertification.The total area of mid-cover alpine grassland and high-cover alpine grassland has decreased by 16.33% from 1969 to 2013.With a trend to increase in periodic drought,the total area of alpine meadow hasdecreased by 3.75% during the same time.Fragmentation and separation of alpine grassland units in the land-scape has been occurring and also shrinkage and disappearance of patches.The rate of degradation increased very rapidly after the 1980s,and reached its maximum in 2000,but has been consistently decreasing since 2000.Climatic drought caused by a warming trend has been the main driver for alpine grassland degradation in the source regions of Yangtze and Yellow Rivers,and overstocking and unreasonable human activity were im-portant contributing factors,intensifying the degradation.