Vertical variability of rock desertification in Karst mountainous areas

The vertical gradient variation of rock desertification index was analyzed using geostatistics for Bijie region,Guizhou province, that exhibits wide altitudinal variation in the centre of Yunnan,Guizhou,Guangxi Karst area.Optimal semivariogram theoretical model of bedrock expose rate was fitted well with linear sill model,and vegetation cover and gravel content were fitted with spherical model.Vegetation cover rate(VCR),which mainly affected by natural control factors correlated with altitudinal variation,was highly related to vertical gradient.The rate of nugget to sill of VCR was 22.32%.Bedrock expose rate and gravel content were mainly affected by random factors,which had moderately relativity with vertical gradient and their rates of nugget to sill were 34.38% and 5.97%,respectively.The altitudinal ranges of gravel content and vegetation cover rate were 968.10 m and 859.48 m,respectively,indicating wide range of altitudinal effect.The altitudinal range of bedrock expose rate was 52.28m,indicating narrow range of altitudinal effect.Similarity was found between the trend of Moran′s I of bedrock expose rate and trend of Moran′s I of vegetation cover rate along altitudinal gradient.However,trend of gravel content showed greater different from the other two.