Environmental Factor Characteristics of Soil Erosion in the Upper Reaches of Shiyang River in the Qilian Mountains

The amount of soil erosion and its spatial distribution features in the Haxi forest area located in the eastern and north slopes of Qilian Mountains were simulated using GIS and USLE.In addition,the responses of soil erosion to natural environmental background were quantitatively analyzed.The study revealed that the annual average soil erosion modulus in the study area is 25.1 t·hm-2·a-1;the area of slight and minor erosion takes up 80 percent of the total erosion area.However,the 78.3% erosion amount comes from strong to severe erosion.According to annual average soil erosion modulus,the land types are ranked from high to low as follows: bare soilgrasslandfarmlandshrubberyhigh forest;the erosion amount of bare land accounts for 54.9% of the total.More than 95% of high forest and shrubbery area is light erosion area;in farmland the erosion intensive is visibly higher than that in grassland and other vegetation types.However,the area percentage of severe erosion of grassland is more than that of farmland.The relationship between amount of soil erosion and altitude has positive correlation with the altitude range of vegetation types.The average soil erosion modulus increases with gradients,and the erosion amount mainly yields from the slope range of 15°～45°.The changing tendency of erosion amount with slope for different vegetation types could indicate the preventing function of vegetation types in a certain extent.