Quantification of spatial distribution of vegetation in the Qilian Mountain area with MODIS NDVI

Abstract

The spatial distribution of vegetation in the Qilian Mountain area was quantified with remote sensing data. The MODIS NDVI values for June, July, August and September are the best indicators for the vegetation growth during a year in this area and thus were used in this study. The results obtained by analysing NDVI data for seven years from 2000 to 2006 clearly indicated that elevation and aspect, as a proxy for precipitation and temperature, are two very important factors for the vertical distribution of vegetation in Qilian Mountain area. In the Qilian Mountain area the vegetation growth is optimal between the elevations of 3200 m and 3600 m, with NDVI values larger than 0.50 and a peak value of >0.56 around 3400 m. It is the combination of plentiful precipitation and suitable land surface temperature that provides less soil moisture stress and thus suitable conditions for vegetation growth in this range of elevations. The optimal vegetation growth is found in the shady slope between NW340° to NE70° with the largest NDVI value (>0.56) within the elevation range of 3200 m and 3600 m. The methodology developed in this study should be useful for similar ecological studies on vegetation distribution.