| The loess plateau as the most serious soil erosion area in china, is the key area that our country conducts ecological restoration and reconstruction; Vegetation is the important factor which cause the soil erosion, studying on the valid expression of the role that the vegetation play in the soil and water conservation has important significance in the ecological restoration and reconstruction in our country.This study takes the Yanhe river basin in the loess hill and gully area as the study area and takes the USLE as the datum. This study chooses the Cs as the Vegetation reference factor to revise the vegetation factors. At the same time, This study take the Vc as the reference factor, and do the comparative analysis on the role that they play in soil erosion. Then the soil erosion intensity was evaluated in the Yanhe river to examine the structural vegetation factor'reliability to assess and predict the soil erosion in the reginal scale basing on the RS and GIS techniques. This thesis has got the initial conclusions as follows:(1) In this study, the relationship between the measured traditional coverage (C) and the structural vegetation index (Cs) was analyzed according to the field investigation data. When the vertical tructure is composed by tree, shrub and herb, the minimum of Cs is 0.39, the minimum of c is 0.6; When there are only two vertical structural layers(tree-herb layer, shrub-herb layer or tree-shrub layer), Cs is between 0.23 and 0.39, the minimum of c is 0.4; When the vertical tructure is single(tree, herb or shrub), Cs is between 0 and 0.23, c is between 0 and 0.4. The regression analysis shows that the Cs and the C has negative correlation relationship.(2) In this study, we calculated the value of R, K, LS and P, The results showed that the value of R is between 4571.95MJ.mm.hm-2.h-1.a-1 and 6438.91MJ.mm.hm-2 .h-1 .a-1, the value of K is between 0.028 t.h.MJ-1.mm-1 and 0.044 t.h.MJ-1.mm-1. the value of LS is between 0.05 and 40, the maximum P is 0.2, the minimum P is 0.234. We constructed the relational model of c and Cs, the rusult show that C is in the range of 0～1 which based on Vc, and C is in the range of 0～0.6 which base on Cs. (3) This study show that the projected cover (Vc) of the high-intensity erosion area is 41.49%, while the structure-based vegetation index (Cs) of the high-intensity erosion area is 73.78%. According to the above results, the cover exceeded 70% is up to 60% in YanHe. so that the structure of vegetation index (Cs) can be used as an ideal reference vegetation factor. The conclusion is defferent from the field survey. We can conclude that the erosion evaluation based on Cs is closer to the factual situation. while.(4) Using fixed-point analysis showed that, when the vertical structure is complete, the soil erosion intensity level is mild; when there are only two vertical layers, the soil erosion intensity level is moderate or extreme intensity; When the structure is single, the soil erosion intensity evel is extreme or very severe intensity, which is particularly in orchard. It can be seen that soil erosion is quite sensitive at the community structure changes; but projected coverage (Vc) level changes in the structure is not sensitive. It is difficult to reflect the change of vegetation structure. The soil erosion which caculated by Vc is far below the actual erosion. |
