Impact of Agroforestry Types-Induced Microtopography on Hillslope Erosion in Alpine Canyon Areas

Abstract

Surface conditions, including vegetation cover and microtopography, affect soil erosion significantly. However, research on the hydrological processes of different agroforestry types on sloping farmland in southwest alpine canyon regions remains insufficient. The microtopographic evolution of different agroforestry types and a bare slope (CK) was investigated by field-based in situ scouring experiments. Agroforestry types were divided into Zanthoxylum + Plum + Canadian fleabane (ZPC), Zanthoxylum + Cherry + Artemisia indica (ZCA), Zanthoxylum + Green bean (ZG) and Plum + Soybean (PS). Structure from motion (SfM) photogrammetry was used to measure the microtopography of each slope under different scour discharge rates (6, 10 and 14 L·min⁻¹). The influence of microtopography on surface runoff and sediment yield was analysed. The results revealed that the ZPC type exhibited the greatest intensity of spatial variation in microtopography, while the PS type showed the smallest. The elevation of each hillslope under different agroforestry types varied from −100 to 100 mm, and the erosion distribution rate accounted for 38.37% to 80.77% of the total. Compared to the pre-experiment, the variation range of soil surface roughness (SSR), surface cutting depth (SCD), surface relief (SR) and microslope (MS) index were −16.49% to 11.56%, −24.79% to 32.32%, −22.72% to 33.44% and −17.36% to 19.42%, respectively. Under different scour discharge rates, the ZPC type effectively reduced runoff, while the ZCA type significantly decreased sediment yield. At a scour discharge of 14 L·min⁻¹, the initial runoff production time of the ZCA and ZPC types was significantly delayed compared to that of the CK hillslope, demonstrating a notable runoff reduction benefit. SSR and MS were positively correlated with sediment yield and runoff. SSR can be used to predict runoff and sediment yield in agroforestry areas. These findings provide a theoretical basis for the effective prevention and control of soil loss and the construction of prediction models for sloping farmland in alpine canyon areas.