Abstract:

Aims: Spatial patterns of biodiversity can reflect the community assembly processes and the mechanisms of species coexistence within ecosystems. The semi-humid evergreen broad-leaved forest is a type of vegetation zone located in the semi-humid climate of the western subtropical region of China. To date, there have been many studies investigating the species diversity of this type of vegetation, but studies into the patterns of spatial heterogeneity of species diversity and its determinants are still relatively lacking, and research utilizing large dynamics plot has not yet been reported. To better understand the maintenance mechanism of species diversity, we explored the characteristics of spatial heterogeneity and species diversity and their main environmental determinants in a 20.16 ha forest dynamics plot located in the Jizu Mountains.

Methods: Based on data collected from woody plants and TWINSPAN classification results from 504 quadrats 20 m × 20 m in the 20.16 ha forest dynamics plot in the Jizu Mountains, this article utilized regression analysis and the Mantel test to analyze the distribution patterns of α and β diversity, and their correlation with respective environmental factors.

Results (1) In the plot, we found that the species richness of the Pinus yunnanensis community and its trees and shrubs were all higher than that of the Castanopsis delavayi community and C. orthacantha community; the C. delavayi community and its shrubs species richness were both higher than that of the C. orthacantha community, while its tree species richness was higher than C. orthacantha community. On the contrary, the Shannon-Wiener value of the C. orthacantha community was found to be the highest among all species, followed by the C. delavayi community, while the value of the P. yunnanensis community was the lowest. Based on the net interspecific relationship index (NRI), the phylogenetic structures of the C. orthacantha community, C. delavayi community, and P. yunnanensis community were clustering, random, and overdispersion, respectively. (2) The factors that demonstrated a universal impact on species richness included the total nitrogen and pH, the relative altitude, and the sum of basal area of woody plants. The main factors affecting the richness of tree diversity included total nitrogen level and pH and the sum of basal area. The dominant factor influencing shrub species richness was the relative altitude, followed by total nitrogen, slope, and the topographic wetness index. (3) The species β diversity pattern showed that differences in species composition and turnover rate increased with increasing spatial and environmental distances, indicating that the more similar the environment, the more similar the community.

Conclusion: This study reflects the significant differences in species diversity and composition between the pioneer P. yunnanensis community and the stable C. orthacantha community and C. delavayi community in the Jizu Mountains forest dynamics plot, which describes the characteristics of species coexistence and species diversity maintenance corresponding to the heterogeneous patches of semi-humid evergreen broad-leaved forests, and provides a basis for further mechanistic investigations.

Key words: Jizu Mountains, α diversity, β diversity, environmental factors, geographically weighted regression model, Mantel test