Vertical distribution of NDVI in typical karst regions of Guizhou and Guangxi

Karst regions in Guizhou and Guangxi are characterized by complex topography and highly variable vegetation coverage. Previous studies commonly focused on the vertical distribution of NDVI from the perspective of the response of climatic factors. Because of the sharp contradiction between human and land, human activities have an important impact on vegetation distribution. This paper uses MODIS13Q1 NDVI data of the year 2010 to characterize vegetation coverage in the karst regions. Based on previous analysis, this paper takes elevation, slope, slope aspect as well as different land uses into account to calculate the NDVI vertical distribution characteristics. Results show that the main land use types in the karst regions include forests, arable land and grassland, and different land use types show different distribution characteristics along with the differences in elevation, slope and slope aspect. The mean value of NDVI is 0.59, among which the NDVIs of forests, grassland and arable land are 0.63, 0.58 and 0.54, respectively. In spatial distribution, the majority of NDVI values in Guizhou vary from 0.5 to 0.6, while those in Guangxi drop from 0.8 to 0.4 from the northwest to the southeast dominated by the range of 0.6-0.7. The distribution feature of NDVI on the vertical gradient is notable, closely related to the vertical zoning of vegetation and the vertical distribution characteristics of different land use types. Altitudinally, NDVI value is the smallest at an altitude of less than 200m, but reaches its largest at 400-600m; at the same time the altitude of Guizhou is higher but the vegetation coverage is lower, and Guangxi has a lower altitude but higher vegetation coverage. In respect of slope gradient, where the slope is less than 35 degree, the arable land, water area and construction land decrease rapidly, but the areas of forests and grassland increase gradually and the NDVI increases accordingly. As for the slope aspect, NDVI is basically the same on slopes with different facing directions, with values on the eastward slopes slightly greater than the westward slopes. These features show that the ecological construction should be carried out according to the terrain characteristics such as elevation and slope as well as the land use types.