Degradation of tree plantations increases soil erosion risk through changes in aggregate stability and vegetation traits

Inappropriate afforestation combined with frequent extreme events has led to degradation of tree plantations globally, which may increase the risk of soil erosion. In this study we evaluated the impact of tree plantation degradation on soil erodibility. To this end, we conducted a study at three sites (Baotaqu, Zichang, and Mizhi) distributed in the semiarid Loess Plateau of China, where the dominant tree species was black locust (Robinia pseudoacacia L.). We evaluated the degrees of degradation of tree plantations by standing dead trees index and set three different levels: T1 level (Standing dead trees index = 9 n ha⁻¹), T2 level (Standing dead trees index = 92 n ha⁻¹), and T3 level (Standing dead trees index = 272 n ha⁻¹). Here, we examined the changes in soil aggregate stability and erodibility index (K factor) under varying degrees of degradation of tree plantations. The results showed that the increase in degradation intensity led to a reduction in the mean weight diameter and geometric mean diameter, along with an increase in the K factor. Soil properties and vegetation traits were strong drivers of soil aggregate stability and the K factor, with soil organic carbon content having the highest explanatory power, accounting for 49.5 % of the variance. The degradation of tree plantations weakened both vegetation traits (σ = −0.45) and soil characteristics (σ = −0.73). This degradation indirectly controls the extent of soil susceptibility to erosion (R² = 0.93). This study provides insights into the assessment of soil erosion risk related to the degradation of tree plantations, which would be further aggravated by ongoing and future climate change.