Jifeng Deng, YJ Li, Yifan Wang, Chang Sun, Yanfeng Bao
In this study, natural Pinus koraiensis Siebold & Zucc. forest, Pinus sylvestris var. mongholica Litv. plantation, Quercus mongolica Fisch. ex Ledeb. plantation, Juglans mandshurica Maxim. plantation, and natural mixed coniferous–broad forests were selected in Qingyuan County. Treeless plots were set as the control check, and comparisons were then made across soil particle size composition, average particle size, standard deviation, skewness, kurtosis, single- and multifractal dimensions, and spatial distribution of soil physicochemical properties and their relationships with fractal dimensions under natural conditions. The results indicated the following: (1) The soil particle size compositions of both the topsoil and sub-topsoil in all forest stands were dominated by sand. (2) The soil particle size was characterized by excellent sorting, skewness, and a narrow peak. (3) The average particle size, single-fractal dimension, and soil physicochemical properties of the forest stands were all higher than those of the control check plots. (4) From coniferous forests to broadleaved forests and then to mixed forests, the aforementioned soil indices showed an overall increasing trend. (5) The single-fractal dimension and capacity dimension were significantly positively correlated with the volume fractions of clay and silt, as well as with soil physicochemical properties. This indicates that the contents of soil clay and silt gradually recovered under the protection of forest stands, with a better recovery effect in the topsoil. (6) Multifractal analysis showed non-uniform soil particle size distribution; thus, evaluating soil quality requires combining single- and multifractal dimensions to characterize physicochemical properties and particle size variation.