Zonal characteristics and attribution analysis of soil erodibility in Robinia pseudoacacia plantations on the Loess Plateau, China

Climate and topography at the zonal scale can significantly influence vegetation and soil properties, which in turn affect the ability of soil to resist raindrops splashing and water erosion. Artificial forests play a key role as ecological barriers on the Loess Plateau. However, the zonal characteristics of soil erosion resistance of Robinia pseudoacacia plantations with the largest planting area in the region and the response mechanism of gradient change of different vegetation zones under mixed management are still unclear. In this study, we selected 13 Robinia pseudoacacia (R p ) pure forest plots, 7 Robinia pseudoacacia ✕ Pinus tabulaeformis mixed forests (R p ✕P t ), 6 Robinia pseudoacacia ✕ Prunus sibirica mixed forests (R p ✕P s ) and 6 Robinia pseudoacacia ✕ Platycladus orientalis Franco mixed forests (R p ✕P o ) mixed forest plots across the steppe, forest-steppe, and forest zones of the Loess Plateau. Based on soil erodibility, we examined zonal characteristics of soil erosion resistance and underlying mechanisms in these plantations. The results show that from the steppe to the forest zone, with the increase of precipitation, the soil erodibility of R p pure forests and R p ✕P t mixed forests shows an insignificant decrease and a first decrease followed by an increase, respectively. Compared with pure forest, mixed forest transformation has enhanced soil erosion resistance, especially R p ✕P o mixed forest in forest-steppe zone. In the correlation analysis, soil erodibility was not directly related to multi-year average precipitation (MAP), but was significantly negatively correlated with altitude, multi-year average temperature (MAT) and litter accumulation. And partial least squares-structural equation modeling indicate that topography indirectly affected soil erodibility by influencing soil nutrients. Climate directly shaped vegetation characteristics, and together, both factors mainly regulated surface soil erodibility indirectly through direct effects on soil nutrients and particle size distribution. This study provides a scientific basis for optimizing forest configurations and ecosystem functions of Robinia pseudoacacia plantations on the Loess Plateau.