Effects of Salsola passerina shrub patches on the microscale heterogeneity of soil in a montane grassland, China

The spatial distributions of water and nutrients were examined in the desert grassland of Helan Mountain to test the hypothesis that the expansion of shrub patches in the grassland is associated with the degree of soil heterogeneity. The results showed that shrub patches significantly increase the water content and nutrient enrichment in surface soil (0-10 cm), and increase the microscale heterogeneity of the soil. Geostatistics analysis indicated that the autocorrelation distances of soil properties, such as water, total nitrogen (TN), organic matter (OM), and pH, are larger than the mean canopy size of Salsola passerina (30±12.3 cm), but less than in the control (enclosed) grassland. This suggests that the spatial distribution of soil properties may be associated with biotic processes in the shrub patch site. Furthermore, the smaller autocorrelation distances (65-382 cm) found for all soil properties indicate an increase in spatial heterogeneity, or potentially degradation, in the enclosed grassland. Based on these results, a conceptual model of montane grassland degradation processes following overgrazing was developed.