Spatial variability of soil thickness and the distribution characteristics of herb and shrub communities in the arid and barren areas of Taihang Mountains

The soil layer is very thin in the arid and barren areas of Taihang Mountains under natural environment. Bare patches were usually formed and soil erosion and other geological disasters frequently occurred here. The coverage rate of natural forest is low and vegetation richness and species diversity are also limited. In order to explore the relationship between soil thickness and the distribution of plant communities, the spatial variability of soil thickness were studied on the northeast and southwest slopes of the dry and barren mountainous areas of the Taihang Mountains by geostatistical methods. And the differences in community distributions, species diversity, and species richness at different soil thicknesses were compared. The results are as follows: 1) the soil thickness was between 0-50 cm, with an average thickness of 11.69 cm and 12.77 cm on the northeast and southwest slopes, respectively. Soil with thicknesses of 0-15 cm accounted for 71.43% and 62.81% respectively on the northeast and southwest slopes of all their soil types. 2) Soil thickness on both slopes showed a patchy distribution but with significant spatial heterogeneity and strong spatial correlation. Moderately strong spatial variation and structural factors were the predominant factors causing the spatial variation of soil thickness. 3) The plants on the studied slopes were mainly herbs and shrubs, and a total of 22 families, 33 genera, and 38 species were present. Where the thickness of the soil layer was below 10 cm, the plants were mainly herbs. Otherwise, the plants were mainly shrubs. Among them, Lespedeza bicolor was the dominant species where the soil layer thickness was 10-20 cm, and Vitex negundo var. heterophylla and Zizyphus jujuba var. spinosus Hu were the dominant species where the soil layer thickness was more than 20 cm. 4) With the increase in soil thickness, plant community composition varied significantly. Where soil thickness was less than 15 cm, species diversity and species richness gradually increased as soil thickness increased, reaching a maximum value where soil thickness was between 10-15 cm. Where soil thickness was greater than 15 cm, species diversity and species richness tended to decrease as soil thickness increased, indicating that soil thickness affects plant diversity and species richness.