Analysis of spatial heterogeneity of Leymus chinensis and Stipa grandis vegetation and soil nitrogen under different grazing intensities

The influence of different grazing intensities on the spatial heterogeneity of Leymus chinensis and Stipa grandis steppe vegetation and soil nitrogen in Bashang area of Hebei Province was studied using analysis of variance and land statistics. The results showed that the variation function of vegetation density and soil nitrogen was mostly accordance with the spherical and exponential model. The spatial distribution of vegetation community density in light grazing and moderate grazing areas and the spatial distribution of soil nitrogen in heavy grazing area were mostly influenced by random factors, while the spatial distribution of vegetation community density in non-grazing and heavy grazing areas were mostly influenced by space structural factors. Grazing reduced the spatial heterogeneity of vegetation density which resulted in that in non-grazing area (sill=0.116 8) was larger than that in the grazing area (average of sill=0.019 5). With the increase of grazing intensities, the spatial heterogeneity of soil ammonium nitrogen and nitrate nitrogen firstly decreased and then increased. Spatial heterogeneity of soil ammonium nitrogen, nitrate nitrogen significantly increased in the heavy grazing area with the sill values of 5.642 0 and 2.681 0, respectively, which were greater than the other three treatments. In conclusion, the spatial distribution of vegetation density had similar variation with the spatial distribution of soil nitrate nitrogen under the same grazing treatment.