Influence of site, stand, and soil factors on sapling regeneration in typical Quercus Forests of Northern China

Introduction This study aims to characterize sapling regeneration in typical Quercus forests in Beijing, investigate the relationship between sapling density and environmental factors, and provide a theoretical basis for sustaining the ecological stability of Quercus forests in northern China. Methods During June–September 2023, sapling density (individuals with diameter at breast height [DBH]1–5 cm) and environmental variables were surveyed across 17 plots in five Quercus forest types. Correlation analysis, random forest variable importance ranking, and multiple linear regression were used to identify key environmental factors affecting sapling density. Results In Q. mongolica stands, sapling density (>1000 stems/ha) and mean DBH were the highest, while the stands of the other four Quercus species each maintained densities below 500 stems/ha with comparable DBH values. Sapling density was positively correlated with total stem number (N), canopy density (CD), and stand density (SD), but negatively with mean DBH (MD) and available copper (ACu). Random Forest analysis ranked the variables with relative importance exceeding 5% in the following order: MD > altitude (AL) > SD > Shannon-Wiener index (H´) > ACu > humus layer thickness (HLT) > N > CD. Multiple linear regression identified slope aspect, SD, and ACu as the primary environmental factors affecting sapling density. Discussion Sapling abundance and growth status vary across Quercus forests in Beijing, with regeneration density co-regulated by multiple environmental factors. Therefore, forest management should integrate both biotic and abiotic factors to promote natural regeneration.