Long-Term Effects of a 35-Year Chronosequence of Salix psammophila Restoration on Soil Particle-Size Distribution and Erodibility in the Hobq Desert, Northern China.

In dryland ecosystems, the restoration of Salix psammophila shrubs plays a vital role in wind erosion control and sand stabilization. However, the temporal dynamics of soil particle-size distribution and erodibility during S. psammophila restoration remain poorly understood. To address this gap, we established a chronosequence of S. psammophila plantations in the Hobq Desert-a temperate desert in northern China-that had been restored for 6, 12, 15, 25, and 35 years, with adjacent shifting sand dunes serving as the control (CK). At each of the six sites, ten replicate plots were established, and soil samples were collected from the 0-20 cm layer, yielding a total of 60 samples. Multifractal parameters and the soil erodibility K factor were calculated to quantify the effects of stand age on particle-size distribution and erodibility. Principal component analysis (PCA) and a Random Forest model were then applied to factors associated for the observed changes. Compared with CK, soil nutrient and fine particle contents increased significantly with increasing shrub age, whereas pH and sand content declined continuously. Specifically, under S. psammophila plantations, organic carbon (OC), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), and alkali-hydrolysable nitrogen (AHN) contents increased continuously with stand age, while the soil texture became progressively finer. During long-term S. psammophila restoration, the ranges of the multifractal parameters D0, D1, D2 and D1/D0 were 0.82-0.91, 0.59-0.71, 0.50-0.58, and 0.70-0.78, respectively. S. psammophila restoration exhibited pronounced multifractal characteristics, which reduced the heterogeneity of the soil particle-size distribution and made the distribution more uniform, thereby resulting in a more stable soil structure and a more balanced ratio of fine to coarse particles. The soil erodibility K factor indicated that soil erosion resistance gradually increased with stand age, with a 23.71% reduction at 35 years compared with CK. Random Forest analysis identified organic carbon (OC), total nutrients (TN, TP), pH, soil particle-size fractions (clay, silt, sand), D1, D2, and vegetation characteristics (aboveground biomass, AGB; plant density, PD) as important predictor variables for soil erodibility (p = 0.01, R2 = 0.961). These findings provide new insights into the mechanisms by which long-term S. psammophila restoration improves soil structural stability and erosion resistance, offering a scientific basis for optimizing vegetation restoration and sustainable desert ecosystem management in arid regions.