Impact of Elevation and Aspect on the Spatial Distribution of Vegetation in the Qilian Mountain Area with Remote Sensing Data

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 analyzing the NDVI data for seven years from 2000 to 2006 clearly indicated that elevation is the dominating factor determining the vertical distribution of vegetation in the area: the vegetation growth is at its best between the elevations of 3200 m and 3600 m with the NDVI values lager than 0.5 and a peak value of larger than 0.56 at 3400 m. The horizontal distribution of vegetation within the zone of 3200 m and 3600 m is significantly impacted by the aspect of hillslopes: the largest NDVI value or the best vegetation growth is found in the shady slope whose aspect is between NW340o to NE70o due to relatively less evapotranspiration. The methodology developed in this study should be useful for similar ecological studies related to vegetation distribution.