Size-gradient differences in the spatial patterns and processes of Pinus armandii in forest lines of Li Mountains,North Central China

Pinus armandii is one of the local dominant trees in forest lines of Li mountains. The population pattern of Pinus armandii in the forest line is greatly influenced by individual size, and individual size has effect on ecological process. Sampling plot 50 m × 50 m was established in Shunwangping Scenic spot of Li Mountains to obtain location and diameter at breast height (DBH), and spatial point pattern method was applied to explore spatial pattern and ecological process of individuals at different sizes. The results showed: (1) Individual size of Pinus armandii had a parabolic distribution, 10–15 cm DBH individuals had most aggregation scales, < 5 cm DBH individuals had least aggregation scales, and the common scale of individual aggregation is r < 10 m. (2) Homogeneous Thomas null model and Inhomogeneous Thomas null model analysis showed that seed dispersal and interaction between seed dispersal and environmental heterogeneity had significant impact on the pattern of all individuals, seed yield of Pinus armandii was the key to the development of the population, Inhomogeneous Poisson null model analysis showed that environmental heterogeneity more significantly affected the pattern of 5–10 cm DBH individuals, the 5–10 cm population was the more critical stage of the survival of Pinus armandii in the forest line. (3) Intra-specific correlation analysis showed that significant positive correlation happened between four size groups (< 5 cm, 5–10 cm, 10–15 cm, > 15 cm), individuals at 10–15 cm had wider positive correlation scales with other three groups, it might be that quantity of individuals in 10–15 cm was greatest. The size difference of individual in species population had a great influence on the pattern, the results could help to understand the significant impact factors and regeneration obstacles of Pinus armandii in the forest line at different stages.