Quantifying surface cracks in alpine meadows is a prerequisite and a key aspect in the study of grassland crack development. Crack characterization indices are crucial for the quantitative characterization of complex cracks, serving as vital factors in assessing the degree of cracking and the development morphology. So far, research on evaluating the degree of grassland degradation through crack characterization indices is rare, especially the quantitative analysis of the development of surface cracks in alpine meadows is relatively scarce. Therefore, based on the phenomenon of surface cracking during the degradation of alpine meadows in some regions of the Qinghai-Tibet Plateau, we selected the alpine meadow in the Huangcheng Mongolian Township, Menyuan Hui Autonomous County, Qinghai Province, China as the study area, used unmanned aerial vehicle (UAV) sensing technology to acquire low-altitude images of alpine meadow surface cracks at different degrees of degradation (light, medium, and heavy degradation), and analyzed the representative metrics characterizing the degree of crack development by interpreting the crack length, length density, branch angle, and burrow (rat hole) distribution density and combining them with in situ crack width and depth measurements. Finally, the correlations between the crack characterization indices and the soil and root parameters of sample plots at different degrees of degradation in the study area were analyzed using the grey relation analysis. The results revealed that with the increase of degradation, the physical and chemical properties of soil and the mechanical properties of root-soil composite changed significantly, the vegetation coverage reduced, and the root system aggregated in the surface layer of alpine meadow. As the degree of degradation increased, the fracture morphology developed from linear to dendritic, and eventually to a complex and irregular polygonal pattern. The crack length, width, depth, and length density were identified as the crack characterization indices via analysis of variance. The results of grey relation analysis also revealed that the crack length, width, depth, and length density were all highly correlated with root length density, and as the degradation of alpine meadows intensified, the underground biomass increased dramatically, forming a dense layer of grass felt, which has a significant impact on the formation and expansion of cracks.

The impact of daily cattle migration from homesteads to higher altitude pastures creates severe erosion in the montane grasslands of the predominantly subsistence agricultural rural communities of KwaZulu-Natal, Drakensberg, South Africa. This study quantifies the impact of a degraded cattle path at up, mid and downslope positions on SOC and N distribution in the soil profile and within the soil aggregates. An attempt to evaluate sites of erosion and deposition using excess lead-210 (210Pbex) to support our findings was conducted. On average, the degraded cattle path reduced SOC and N in the bulk soil (by 3-4 times, respectively) and was associated with 53% reduction in aggregate stability and a 14% increase in soil bulk density over the non-degraded reference site. These results reflect the loss of vegetation cover (correlated positively to SOC and N (r approximate to 0.94)), which were triggered by cattle grazing and trampling leading to top-soil loss. Cattle hoofs damage the grass and breakdown soil aggregates, exposing the fertile topsoil particles to detachment and consequential transportation via rill and sheet erosion. This is supported by the loss of 210Pbex in the topsoil of the degraded slope positions relative to the reference site. Consistent down core mixing of 210Pbex activity in degraded slope sites supports evidence of cattle mediated soil mixing. Our findings highlight the accelerated land degradation that results from uncontrolled grazing and movement of cattle on sloping lands in the Okhombe Valley. Developing an integrated management strategy co-led by local communities to develop proactive participatory sustainable land use practices is critical for long-term landscape maintenance and recovery in the region.