Abstract:

Aims The spatial distribution patterns of plant populations result from the combined effects of multiple ecological processes, such as dispersal limitation and environmental filtering. The plants distributed in alpine treeline ecotones are highly sensitive to climate change due to their unique habitats. Therefore, studying the spatial distribution patterns of these plants and their correlations is critical for understanding and predicting the dynamics and trends of forest communities in alpine treelines.

Methods This study is based on the inventory data collected from a 20 hm²dynamics plot of a subalpine cold-temperate coniferous forest in Shangri-La, Yunnan, China. The dominant tree species identified were Abies georgei, Lonicera tangutica, Dipelta yunnanensis, Rhododendron rubiginosum, and Sorbus rehderiana. The spatial point pattern method was used to analyze the spatial distribution pattern of each dominant species, the intraspecific association of A. georgei at different developmental stages, the interspecific association between A. georgei and the other dominant species, and the interspecific association among the other dominant species. Additionally, the Torus-translation method was applied to test the associations between these plants and topographic factors.

Important findings (1) Sapling and juvenile trees of A. georgei demonstrated aggregated distributions, primarily driven by dispersal limitation and habitat heterogeneity. In contrast, adult trees exhibited a predominantly random distribution, suggesting that density-dependent competition may be the primary factor influencing the distribution of individuals in large-diameter classes. The dominant species in both the subtree layer and shrub layer also demonstrated aggregated distribution. However, the posterior partial advantage of the environmental heterogeneity transformed into a random distribution, indicating that environmental filtering might be responsible for driving the spatial distribution pattern of these tree species. (2) Positive associations were observed between sapling and juvenile trees of A. georgei indicating that small-diameter individuals tend to congregate due to an enhanced capacity to cope with external environmental stresses. Conversely, saplings and juvenile trees were negatively correlated with adult trees. This was mainly due to the infestation of specific pathogens and phytophagous insects caused by density constraints and asymmetric competition of large individuals against smaller ones. (3) There were positive and negative correlations between the saplings and the dominant species in the subtree layer and the shrub layer, respectively. The juvenile trees and other dominant species revealed predominantly negative correlation, while the adult trees showed predominantly positive correlation. The majority of the dominant species in the tree layer and shrub layer exhibited positive correlation, indicating a complex dynamic balance within the dominant species in the subalpine cold-temperate coniferous forest. The long-term coexistence of each dominant species in the plot is achieved through their unique survival strategies and resource utilization, and ultimately leading to the formation of a relatively stable successional climax community dominated by A. georgei. (4) Slope was found to be significantly negatively correlated with sapling and juvenile trees of A. georgei, and significantly positively related to R. rubiginosum and D. yunnanensis. This suggests that the slope ecological niche differentiation occurred between A. georgei and other dominant species. Additionally, convexity was found to exert a significant effect on the distribution of dominant species due to adverse conditions such as prolonged snowpack in winter. In conclusion, the habitat filtering driven by topography is the main driver that maintains community assembly in subalpine cold-temperate coniferous forests.

Key words: Abies georgei, spatial point pattern, spatial association, habitat association