Influence of topographic factors on the distribution of herbaceous vegetation and mechanical root properties of the Xijitan giant landslide in the upper reaches of the Yellow River, northwestern China

Abstract Background The upper reaches of the Yellow River, located on the northeastern Qinghai-Tibet Plateau, host numerous giant landslides characterised by sparse vegetation cover and a fragile ecological environment. Along the Longyangxia-Jishixia river corridor, critical infrastructure such as the Longyangxia, Laxiwa, Lijiaxia and Gongboxia hydropower stations depends on the ecological and geological integrity of these slopes, which also support the livelihoods of local communities. However, the ecosystem characteristics of giant landslide areas in the upper Yellow River remain poorly understood, particularly regarding how locally dominant herbaceous species and their root mechanical properties influence the shallow stability of these landslides. Methods Focusing on the Xijitan giant landslide in the upper reaches of the Yellow River, we combined field vegetation surveys with laboratory single-root tensile tests. We analysed how topographic factors structure plant community distribution patterns, with particular emphasis on the effects of slope aspect on root morphological traits and biomechanical properties of dominant herbaceous species. Results Fresh biomass and ground cover decreased with increasing solar exposure, following the sequence shady slope > semi-shady slope > semi-sunny slope > sunny slope under otherwise comparable conditions. Principal component analysis identified slope aspect as the primary topographic factor controlling herbaceous community composition, and its associated axis 1 explained 67.74% of the community variance. Slope aspect influenced plant root mechanical properties by altering habitat conditions, which not only affected the aboveground community structure but also affected the structural morphology of the root system. The results of single-root tensile tests further showed that there were significant differences in the mechanical properties of roots between sunny and shady slopes. Specifically, the tensile strength of Poa araratica roots in sunny slope habitats was 25.77 MPa, significantly higher than that in shady slopes (24.38 MPa). Stipa aliena exhibited the same trend, with a higher tensile strength on sunny slopes (30.52 MPa) compared to shady slopes (28.75 MPa). These results reflect that the habitat differences caused by slope aspect drove the changes in the root mechanical behavior of herbaceous plants. Conclusion This study demonstrates a clear link between slope aspect, herbaceous community distribution and the mechanical properties of plant roots on a giant landslide. The findings provide essential theoretical support for ecological restoration in landslide-prone regions and offer a scientific basis for using vegetation to control slope soil erosion and mitigate shallow landslide risk in the upper reaches of the Yellow River basin.