Alpine Grassland Degradation in the Source Region of Yangtze River in the Past 30 Years——Zhidoi County as A Case Study

Alpine grassland in hinterland of the Tibetan Plateau is unique and the largest fragileecosystem at the highest altitude in the world.It has degraded continuously and therefore attractedinterests of scientists.It’s the important material base for the development of plateau husbandryand ecological protective screen for water conservation,biodiversity conservation and carbonfixation.However,the degradation of alpine grassland not only decreased animal husbandryeconomy,but also resulted in desertification,biodiversity loss,aggravated soil erosion and carbonlosses.Having integrated the Landsat images in 1970s,1990s and 2004,meteorological data,DEM,grassland distribution and social statistics data,we took Zhidoi County in Qinghai Provinceas the typical alpine grassland in the source region of Yangtze River to analysis the spatial-temporalpattern,processes and driver,and the degree and mechanism of degraded grassland in order toprovide scientific basis for the recovery and management of alpine grassland and regionalsustainable development.The results show that grassland degradation is presented by decreasingarea,reducing degree and compound type to single type from the southeast to northwest of ZhidoiCounty.Such similar trend is also shown in the status and redistribution water and heat resources inthis region.The eastern part of Zhidoi suffers the most serious degradation,and western part innorthern Tanggula Mountain mainly suffers slight decrease in coverage due to minor underlyingsurface.The general trend of temporal process shows continuous degradation with furtheraggravation during the latter period.The proportion and degree also aggravate gradually with netincrease of 9.86%form 1990s to 2004 compared with the period of 1970s to 1990s.Despite of theobvious warming and drying trend since 1960s,climate change has affected the grasslandchronically and slowly.We found that the degradation patterns of grassland was formed before1970s and aggravated since 1990s,due to the intra-annual distribution of precipitation especially ingrowing seasons.It was also realized that human activities,especially overgrazing,appeared to bethe primary cause of grassland degradation based on the analysis of population and livestock.Theshady slope in the altitude ranging from 4500 to 4900m and slope of 5%~15oappeared to be themain degraded region,where 39.21%degradation located in the slope of 5%~15oand 43.55%inshady slope.Degradation aggravated as altitude goes higher but it turns to decrease when thealtitude is above 4900m.