Driving Factors of Chinese Pine Population Distribution in the Ridge Habitats of the Southern Slope of the Mid-Qinling Mountains, China

The Chinese pine (Pinus tabuliformis) community on the ridge is one of the most important zonal forest communities on the southern slope of the mid-Qinling Mountains. This study aimed to investigate the driving factors of Chinese pine population distribution in the ridge habitats and its adaptability characteristics. Population age structure and the relationship between regeneration dynamics and environmental factors were investigated in 32 plots in the Huoditang Forest region. The results showed that the niche of Chinese pine was wide but overlapped greatly with that of Quercus aliena var. acutiserrat, an oak species. The population in the ridge habitats exhibited an expansion trend, while that inhabiting slope habitats was declining. Seedling density in ridge habitats was much higher than that of the understory in the slope habitats. Still, the seedling growth rate in both ridge and understory habitats was much lower than that characteristic of gap habitats. Seedling density positively correlated with understory solar conditions, while growth positively correlated with soil fertility, indicating that environmental factors significantly influence the regeneration process. Thus, light conditions and intrinsic biological traits of Pinus tabuliformis influence its distribution. In ridge habitats, sufficient light conditions promote Pinus tabuliformis regeneration and recruitment of larger classes, but poor soil conditions also limit its growth.