Spatial pattern analysis reveals intra-specific competition and fractal characteristics of Pinus sylvestris var. mongolica populations in Xiaotaojia Gulley Watershed

Abstract

The imprudent cultivation of Pinus sylvestris var. mongolica has led to degradation in the watersheds surrounding Chongli County. This study investigates the artificial forests of P. sylvestris var. mongolica in the Xiaotaojiagou watershed, Chongli County. Twenty-five subplots measuring 20 m × 20 m were established at upper, upper-middle, middle, and lower positions within the watershed. Spatial distribution patterns and fractal characteristics of P. sylvestris var. mongolica were analyzed using univariate pair correlation function g(r), marked correlation functions (marked correlation function Kmm(r), marked variation function γm(r), and Schlather’s Im(r) function), and fractal dimensions (box-counting dimension, information dimension). The findings are as follows: (1) P. sylvestris var. mongolica in the middle section of the watershed displayed the largest average diameters at breast height and tree height, while those in the lower section exhibited the largest average crown width. (2) P. sylvestris var. mongolica populations in the upstream, middle, and downstream sections of the watershed exhibited three alternating states: aggregated distribution, uniform distribution, and random distribution. However, with increasing spatial scale, the distribution gradually tended towards randomness. P. sylvestris var. mongolica in the upper-middle section of the watershed showed aggregated distribution at scales of 1.5–32.5 m, transitioning to random distribution and then to uniform distribution with increasing spatial scale. (3) Individual attributes of P. sylvestris var. mongolica (diameter at breast height, tree height, and crown width) exhibited high correlation and facilitation in the upstream and upper-middle sections at small-to-medium scales, whereas negative correlations and inhibitions were observed in the middle and lower sections. These attributes tended to be uncorrelated with increasing spatial scale. (4) Fractal dimensions indicated that the degree of aggregation of P. sylvestris var. mongolica population was lowest in the downstream section of the watershed. In conclusion, spatial distribution patterns and intraspecies relationships of P. sylvestris var. mongolica populations are influenced by spatial scale and environmental conditions, particularly in more resource-competitive downstream areas. Effective management and protection of P. sylvestris var. mongolica populations require targeted measures such as adjusting afforestation density, improving soil conditions, and implementing differentiated ecological restoration strategies to alleviate intraspecies competitive pressures and promote population health and sustainable development.