Abstract

The shear characteristics of soil–root systems are dynamic indicators for assessing soil erosion resistance. Vegetation type influences shear characteristics by altering soil properties and root traits. However, the mechanisms by which mixed vegetation roots affect shear characteristics remain unclear. We selected naturally restored forestland (with Dicranopteris dichotoma, Baeckea frutescens, and their combinations) and artificially managed orchard systems (with Paspalum wettsteinii, Gardenia jasminoides, and their combinations) in the erosion-prone red soil region of southern China. In situ shear tests were conducted to explore the shear characteristics of soil–root systems under different vegetation types, identify the main influencing factors, and clarify the underlying mechanisms. Shear fracture energy (SFE), peak shear stress (PSS), and peak shear stress displacement (DPS) decreased with increasing soil depth across all sites. The average SFE and PSS in the forestland were 2.44 and 3.11 times higher, respectively, than those in the orchards. The main factors influencing shear characteristics in forestland included root volume density, tensile strength, bulk density, and mean weight diameter of aggregates (MWD), whereas those at the orchard sites included root length density, tensile strength, and organic matter content. Root factors had a stronger impact on shear fracture energy than soil properties. Shear fracture energy equations were constructed for forestland and orchard sites, showing high R2 and Nash–Sutcliffe efficiency values, indicating adequate predictive performance. These findings contribute to our understanding of the mechanical mechanisms of soils under vegetation restoration, provide scientific evidence for soil and water conservation evaluations, and help optimize vegetation restoration strategies in the Southern Red Soil Region.

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