A Structural Equation Model Suggests That Soil Physical Properties Had the Greatest Negative Influence on the Competition Index of Dominant Trees of Pinus sylvestris var. Mongolia

Abstract

This study was conducted in a Pinus sylvestris var. Mongolia plantation within the Xiaotaojiagou watershed of the Winter Olympic venues (Chongli competition area) to explore the influence of forest growth factors, soil physical properties, soil nutrients, and other factors on the competition index (CI) of dominant trees in the plantation. A 20 m × 20 m sample square was established every 300 m, and a total of 20 plots were set. The Hegyi single-tree competition index model and structural equation model (SEM) were used to analyze the dominant tree CI and its association with the forest growth factor, soil nutrient content, and soil physical properties. The CI of Pinus sylvestris var. Mongolia showed a decreasing trend with increases in the forest growth factor, the soil nutrient content, and the soil physical properties. Soil physical properties had the greatest influence on the CI, with a significant negative correlation (p < 0.05) and a total effect of −0.91. The results indicate that the competition index of dominant trees is sensitive to changes in soil physical and chemical properties as well as growth indicators such as diameter at breast height, tree height, and crown width of Pinus sylvestris var. mongolica.

Effects of Anthropogenic Disturbance on the Structure, Competition, and Succession of Abies ziyuanensis Communities

“…Unlike the basic competition index (CI), WCI offers a nuanced depiction of competitive interactions between smaller and larger trees. Our analysis revealed a negative correlation between the competition pressure faced by Abies ziyuanensis and the average DBH across all populations, aligning with conclusions from previous research [36,37]. The significant impact of spatial competition among trees on individual growth conditions, particularly in terms of resource allocation and niche occupation [42], is underscored.…”

“…A higher competition index indicates greater competitive stress on a tree [32][33][34][35]. Studies have shown a negative correlation between competition indices and DBH, leading this research to employ the differential DBH relationships between target and competing trees to weight the competition index of the target tree [36,37]. The competitive unit is determined using Voronoi diagrams.…”

“…These individuals, benefiting from early growth advantages, have already occupied favorable niches, thereby reducing direct competition with surrounding vegetation. Conversely, smaller individual trees face greater competition pressure due to less favorable positions or slower growth rates, making it challenging for them to secure sufficient resources [36]. Anthropogenic interventions, by altering forest structure and resource distribution, lead to changes in the ecological competition pattern among trees.…”