Vertical Variation in Species Dominance and Interspecific Associations in a Vatica mangachapoi Community

This study investigated a Vatica mangachapoi community in the Bawangling area of Hainan Tropical Rainforest National Park. We analyzed the 20 woody species with the highest importance values in each of the four forest layers to compare species dominance, plot-level distributional patterns, and interspecific associations. The results showed that: (1) Vatica mangachapoi ranked first in importance value in the large, medium, and small arbor layers and second in the shrub layer, while exhibiting the greatest niche breadth in all four forest layers, indicating its prominent position in the community and relatively widespread and even distribution of importance values across plots. (2) Niche overlap was common among dominant species, particularly in the small arbor layer, but high-overlap pairs remained rare (<8% in each layer). All layers exhibited significant positive overall associations, and positive pairwise association coefficients predominated, although few pairs were significant in Fisher’s exact tests. After Benjamini–Hochberg correction, only three species pairs retained significant positive Spearman correlations, two with high niche overlap. (3) Within each layer, Pianka overlap and Spearman correlations were positively related, reflecting concordance between indices derived from the same plot-level importance-value data. These findings reveal differences in species dominance, plot-level co-occurrence, and covariation across forest layers in the surveyed Vatica mangachapoi community, providing a basis for future monitoring.