The change characteristics of grassland vegetation and the assessment of grassland function on water and soil conservation in the source regions of Yangtse River and Yellow River

Using from 1995 to 2004 the observation data fixing position in 3 animal husbandry meteorological observation stations-Henan,Qumalai, Gande of the source regions of Yangtse River and Yellow River,The change characteristics of grass growth stages,height,yield and population structure were analyzed.The results indicated that the grass regreening stage and withering stage changed,what resulted in grass growth stage prolong 3 to 5 days.According to the analysis about grass height,yield and population structure,the tendency and the degree of grass degraded were weak in Qumalai of source region of Yangtse River;but grass in the source region of Yellow River displayed the certain degradation trend,and the grass degradation in Henan was especially remarkable.Through analyzing the coefficient of the grassland water and soil conservation computed by the vegetation coverage,we found that the mean index of coefficient was 0.66 in the source regions of Yangtse River and Yellow River,and from east to west it appeared the diminishing tendency,and the low value appeared in Zhiduo county,and the high value was in Henan county.The grassland function on water and soil conservation was good in Jiuzhi county,Banma county,Gande county,Henan county and Zeku county,and it was poor in Zhiduo county,and in the other regions it was relatively poorer.