三江源区东部8县草地退化格局分析

Degraded Grassland Patterns of Eastern Eight Counties,Source Regionof the Three Rivers,Qinghai Province

利用3期遥感影像（20世纪70年代末MSS，20世纪90年代初和2004年TM），借助1：100000地形图、1：1000000草地图和植被图以及野外考察景观照片，对三江源区东部8县的草地退化状况进行分析，结果表明：①东部8县草地退化，总体为轻微退化类型区，退化趋势减弱。轻度破碎化草地、轻度破碎化和轻度覆盖度下降草地类型占该区总退化类型面积的63％；②轻度退化草地以阿尼玛卿山地周围所占比例最大。中度退化草地主要位于西部和南部山体的阳坡、半阳坡，而在阴坡上很少发现。重度退化草地多数分布于河流、居民点周围；③海拔3700～4500m之间是草地退化主要发生区，两时段退化草地面积分别占总草地面积的11．88％和8．01％，而8°～25°也集聚了东部8县主要草地退化类型；④草地退化比重由20世纪70年代末到90年代初的11．2％减小为20世纪90年代初到2004年的9．8％，但草地退化趋势仍在持续；⑤研究有助于从本底上准确把握三江源区草地退化状况，进而认识源区主体生态系统本底状况。

Using three-term remote sensing images （i. e. , MSS in the 1970s and TM in the 1990s and 2004）, 1：100000 topographical map, 1： 1000000 grassland map and vegetation map, and field landscape photographs, this paper analyzed the patterns of degraded grassland of eastern eight counties, the source region of the three rivers. The results indicated that degraded grassland presented generally slight degraded characteristics, and the tendency of degraded grassland became lower. Slight fragment grassland area to total grass area accounted for 63%. Slight degraded grassland mainly occurred in the peripheries of Anyemaqen Mountains. Moderately degraded grassland occurred on the sunny and subsunny slope of western and southern mountainous. Seriously degraded grassland are mostly distributed in the vicinities of rivers and residential area. During the 1970s - 1990s and the 1990s -2004, degraded grassland area accounted for 11.88% and 8.01% of the total grassland area at the elevations of 3700 -4500 m, respectively. Slope land with a gradient of 8 -25° belonged to primarily degraded grassland types. Degraded grassland area in the 1990s -2004 was 639492 ha, accounting for 9.8% of the total grassland area, while it was 727553 ha （ 11.2% ） in the 1970s - 1990s. Obviously, grassland degradation in this area still continues. This study favored to accurately grasp current situation of grassland degradation, thereby understand the main ecosystem health conditions in the source region of the three rivers.