Abstract:[Objective] This study aimed to reveal the relationship between fractal characteristics of soil particle size distribution and soil properties in different forest types in typical karst regions of Guangxi, and provide scientific guidance for sustainable forestry development in rocky desertification areas. [Methods] The particle size distribution and properties of the soil in Eucalyptus, Pinus massoniana plantations, and natural secondary forests were determined. The single and multiple fractal dimensions of soil from different forest types were calculated using the fractal models, and the correlations between the fractal dimensions and soil properties were explored. [Results] Compared to natural secondary forests, the bulk density of Eucalyptus and Pinus massoniana plantations was lower by 23% and 15%, respectively. The total porosity increased by 27% and 17%, respectively. The clay content decreased by 58% and 42%, while the sand content increased by 24% and 14% for Eucalyptus and Pinus massoniana plantations, respectively. Additionally, the single fractal dimension (Ds) decreased by 6% and 4% for these two types of plantations. Furthermore, the contents of available phosphorus, readily available potassium, and total calcium all decrease. Specifically, the reductions for Eucalyptus were 68%, 49%, and 6%, respectively, while for Pinus massoniana, the reductions were 42%, 40%, and 25%, respectively. D0-D2、ΔD and Δα are the multifractal parameters that reflect the heterogeneity of soil particle size distribution across different dimensions. The values of these three parameters for Eucalyptus (0.13, 1.29, 1.52) and Pinus massoniana (0.13, 0.99, 1.18) plantations were both higher than those for the natural forests (0.08, 0.83, 1.02). Furthermore, there was a more significant correlation between the multifractal parameters and soil nutrient content in the plantations. [Conclusion] The improper cultivation and management of plantations in the karst regions may promote the loss of soil fine particles and the depletion of key nutrients. This, in turn, can result in a concentration of soil particle size distribution in low-probability dense areas, increasing the heterogeneity of soil particle size distribution, and further accelerating the process of rocky desertification. The single fractal dimension Ds can reflect the degree of soil fertility degradation in karst forest areas, and the multifractal parameters can reveal the heterogeneous distribution characteristics of soil particle size at the micro-level in detail. Therefore, the single and multiple fractal dimensions have the potential to become precise indicators for evaluating the soil quality of plantations in karst regions.