Surface roughness response of biocrust-covered soil to mimicked sheep trampling in the Mu Us sandy Land, northern China

Abstract

Surface roughness plays an important regulatory role in the interactions and feedback between the soil surface and atmospheric systems. However, information regarding the response of surface roughness to trampling disturbances caused by sheep grazing is limited, especially in sandy soils covered by biocrust. This study investigated the covariations in the roughness, coverage and shear strength of cyanobacterial crust (CC), algae-lichen mixed crust (LC) and moss crust (MC) on both the semi-fixed and fixed dunes at the southern edge of the Mu Us Sandy Land, northern China, under various trampling intensities using field studies and mimicked sheep trampling disturbances. The results showed that the surface roughness of semi-fixed and fixed dunes decreased after an initial increase with increasing trampling intensity, and the surface roughness of the fixed dunes was higher than that of the semi-fixed dunes. In addition, with the increasing trampling intensity, the maximum surface roughness (Rmax) and its corresponding trampling intensity of the biocrust-covered soils at different development stages followed the order of CC, LC, and MC. The grazing intensity (G) corresponding to Rmax values in both the semi-fixed and fixed dunes at different development stages of biocrust was 9.6 to 14.4 and 11.1 to 14.4 animal unit day/ha, respectively. The biocrust coverage and shear strength decreased exponentially with increasing trampling intensity and significantly affected the sensitivity of surface roughness to changes in trampling strength. Moderate grazing (grazing intensity less than G) was beneficial for increasing the surface roughness of biocrust-covered sandy land. Increased surface roughness has positive and negative impacts on the ecological and hydrological functions of biocrust-covered soil. To minimize the negative effects of moderate grazing on surface soil, the dune fixation degree, biocrust development level, trampling time and interannual precipitation variability should be considered. This study highlighted the role of grazing management in enhancing the surface roughness and associated ecosystem functions of semiarid regions similar to the Mu Us Sandy Land.