Effects of Strip Clearcutting and Replanting on the Soil Aggregate Composition and Stability in Cunninghamia lanceolata Plantations in Subtropical China

Strip clearcutting and replanting are important methods for optimizing the structure of low-efficiency plantations, but their effects on soil aggregate properties remain unclear, especially in subtropical China, which experiences high levels of rainfall and high erosion risk. This study investigated changes in soil aggregate composition and stability through strip clearcutting and replanting treatments in Cunninghamia lanceolata plantations. The experimental treatments included clearcutting strips with widths of 10 m, 20 m, and 30 m and replanting with evergreen broadleaf Schima superba (SM10, SM20, and SM30) and deciduous broadleaf Liquidambar formosana (SF10, SF20, and SF30), respectively. The reserve belts were set at 15 m (S15), 30 m (S30), and 45 m (S45), with no clearcutting as the control (NT). The results indicated that soils of the treatment plots were dominated by >5 mm aggregates (57%–77%), however, lower than the control (NT) due to the clearcutting and replanting, except SF20 and S15 of reserve belts. The 20 m strip width with Liquidambar formosana replanting (SF20) demonstrated optimal soil structural stability, with significantly lower erodibility K values than the control. The content of >5 mm soil aggregates was significantly positively correlated with the mean weight diameter (MWD) and geometric mean diameter (GMD) and significantly negatively correlated with the erodibility factor (K). In contrast, the contents of the other particle sizes were significantly negatively correlated with the MWD and GMD and significantly positively correlated with the erodibility factor (K). This study demonstrates that 20 m strip clearcutting with Liquidambar formosana replanting (SF20) optimally maintains soil aggregate stability and reduces erosion risk, providing critical evidence for strip width configuration and species selection in ecological restoration of subtropical low-efficiency plantations.