Abstract:

Objective: The aim of this study is to explore the effects of tree species diversity on intraspecific, interspecific, and total competition intensity in natural Pinus massoniana forests, so as to provide a scientific basis for establishing coordinated interspecific relationships in P. massoniana forests. Method: The natural P. massoniana forests in Ganzhou City, Jiangxi Province was targeted, and three tree species diversity indices, including Patrick richness, Shannon-Wiener diversity, and Pielou evenness, were divided into low, medium, and high levels. The eight-neighborhood translation method was used to select the objective trees, the Voronoi diagram method was used to determine the competition range of the trees, and the Hegyi competition index (CI) was used to calculate the intraspecific and interspecific CI of different diameter classes. The CI across different tree species diversity levels and their relationships with DBH of the objective trees were compared and analyzed. Result: 1) Across the three tree species diversity indices (from low to high), the dominant species remained largely unchanged, primarily consisting of P. massoniana, Schima superba, and Cunninghamia lanceolata. Except for Pielou evenness, the proportion of objective trees and competitive trees (with D≥15 cm) for Patrick richness and Shannon-Wiener diversity generally increased with higher diversity levels. The ranking of intraspecific, interspecific, and total CI for each index was roughly consistent with the proportion of objective trees and competitive trees, decreasing as the diversity level increased. The average intraspecific CI generally declined with higher diversity levels, while the average interspecific CI showed the opposite trend. The numerical proportion of intraspecific and interspecific CI across different diversity levels was primarily concentrated in the 5≤D<20 cm range. 2) Under different tree species diversity levels, the numerical proportion of intraspecific CI was higher than that of interspecific CI, accounting for 56.71%–81.67% of the total CI. Among interspecific CI, S. superba had the largest proportion, contributing 41.32%–78.05% to interspecific CI. 3) Across different tree species diversity levels, except for the relatively better fit of the exponential function in the medium Pielou evenness level for interspecific CI, the power function performed relatively better in fitting intraspecific, interspecific, and total CI with objective tree DBH, all showing a gradually decreasing trend as the objective tree DBH increased. Conclusion: In natural P. massoniana forests, the primary competitive pressure within the stand originates from intraspecific competition, with S. superba as the main contributor to interspecific competition pressure. The increase in tree species diversity promotes the growth and survival of large-diameter trees, alleviates the intraspecific competitive pressure on objective trees, and increases their interspecific competitive pressure. This process shifts the stand toward a more balanced trend between intraspecific and interspecific pressure. Therefore, the key to achieving sustainable forest management is to adopt management measures such as tending and thinning, and create forest stands with rich tree species and reasonable structure.

Key words: Pinus massoniana, tree species diversity, intraspecific competition, interspecific competition, competition intensity