Ecological Function Evaluation Of Urban Vegetation Fraction Based On Remote Sensing In Beijing

Urban vegetation is indispensable in urban ecology and landscape. It is an important factor and guarantee for improving life quality in urban area. Therefore, the quantitative analysis of urban vegetation fraction can monitor, evaluate urban green spaces and provide references for decision-making.Based on the existing standard evaluation system about urban green space in Beijing, combined with the remote sensing data characteristics, this article selects the evaluation index of ecological functions of urban green space. Using NDVI data deriving from 4 temporal TM imageries, this paper quantitatively analyzes the spatial-temporal change of vegetation fraction of the study area which is in the downtown of Beijing from 1992 to 2008. The data that the NDVI data in 8 districts and the movement of the focus of vegetation fraction can visually represents the change trend of the ratio of vegetation occupying. Based on method integrated by the gradient analysis and dynamics of vegetation fraction model, the spatial-temporal change of the density of vegetation fraction was analyzed at 4 axial directions which are all cross the center point of the study area. The profile alignment and the level of the changes in regions of vegetation fraction can reflect the pattern about spatial distribution and temporal evaluation. Combined the rate of vegetation fraction and corresponding change of vegetation fraction density with their weight, a comprehensive evaluation was addressed for the ecological functions of vegetation fraction.The results show that the ecological functions of vegetation fraction decreased from the city center to the edge in the study area. During 1992-2003, the rate of vegetation fraction had significantly reduction, and increased in the flowing 5 years. The regions in which a large number of vegetation decreased mainly distribute in the east and the north in the study area. In addition, the lands around urban road network were more affected than in other areas. A lot of green spaces changed into urban construction land. The ecological functions in Xuanwu district has the lowest score in the evaluation of vegetation fraction among the 8 districts in the study area. Haidian district has the highest score, and both the rate of vegetation fraction and the vegetation fraction density are higher than any other districts.