The Research About Dynamic Change Of Vegetation Coverage And It’s Estimation In Cha-Kou Small Watershed On The Loess Plateau Wang Jianlei

Vegetation is an organic part of ecological system, there’s no substitute for primary producers. Vegetation can reduce the intensity of wind erosion and water erosion, etc., thus maintaining the stability of regional ecosystem. Vegetation coverage is the vegetation’s vertical projection area of percentage of the total area in statistical area, including leaves, stems, branches, etc.It has been widely used in global change, soil and water conservation, botany, ecology, and many other research fields, can be measured at different scales, different scale of global area about ecological environment change. Dynamic, rapid and accurate for vegetation coverage information of regional ecological risk assessment, soil and water conservation, soil erosion quantitative estimation, the ecological environment monitoring vegetation factor data, is important.First, this paper applies the improved Dimidiate Pixel Model method to calculate the vegetation coverage based on SPOT5 images in 2003, according to the random sampling data of vegetation coverage and at the same time registration NDVI, SAVI based on TM image data, build the BP neural network, and then use the BP neural network method for estimating vegetation coverage, finally compare the two methods, the results show that by using the BP neural network in this paper, the effect in central basin is good, the correlation coefficient is 0.690, the north and southeast area of basin, Dimidiate Pixel Model method is good, the correlation coefficient of 0.795 and 0.617. Due to lack of other years data validation, this paper decides to adopt Dimidiate Pixel Model method estimate vegetation coverage in 2003,2008 and 2013, respectively is 57.06%,62.30%,66.88%. And on the basis of the result analysis of vegetation cover dynamic change from 2003 to 2013, the area of the vegetation coverage to reduce is relatively small, the area that do not change and increase is larger; Vegetation coverage change was remain stable on the whole basin, and the implementation of returning farmland to forest policy in the small watershed has obtained the good effect.Analysis of the different elevations of vegetation coverage Using DEM data, vegetation coverage was high about 85.33%,in the 1100 m to 1300 m; In extracting, on the basis of using the gradient and slope direction and land use information in 2003,2008 and 2013, analysis the vegetation coverage in different gradient and slope direction, different slope vegetation coverage had no obvious correlation, greater than 25 °average vegetation coverage was high; In terms of slope direction, area of vegetation coverage in Shady-slope is higher than sunny slope; the vegetation coverage change in different land use, forest land vegetation coverage is the highest, arbor is higher than the shrub, open woodland and forest planting area, high density grass coverage is high than low grass.Conclusions are as follows:the implementation of returning farmland to forest policy has achieved good results in the chakou small watershed, from 2003 to 2013, vegetation coverage situation of chakou small watershed has improved markedly, high vegetation coverage area of basin increased significantly in the decade from 2003 to 2013, and average vegetation coverage in different elevation, gradient, slope direction is on the rise.