Studying spatial patterns and habitat association of plant communities may provide understanding of the ecological mechanisms and processes that maintain species coexistence. To conduct assessments of correlation between community compositions and habitat association, we used data from two topographically different plots with 2 ha area in tropical evergreen forests with the variables recorded via grid systems of 10 × 10 m subplots in Northern-Central Vietnam. First, we tested the relationship between community composition and species diversity indices considering the topographical variables. We then assessed the interspecific interactions of 20 dominant plant species using the nearest-neighbor distribution function, D_ij(r), and Ripley’s K-function, K_ij(r). Based on the significant spatial association of species pairs, indices of interspecific interaction were calculated by the quantitative amounts of the summary statistics. The results showed that (i) community compositions were significantly influenced by the topographic variables and (ii) almost 50% significant pairs of species interactions were increased with increasing spatial scales up to 10–15 m, then declined and disappeared at scales of 30–40 m. Segregation and partial overlap were the dominant association types and disappeared at larger spatial scales. Spatial segregation, mixing, and partial overlap revealed the important species interactions in maintaining species coexistence under habitat heterogeneity in diverse forest communities.

Structural complexity and local biodiversity of species-rich tropical forests can be characterized by their spatial patterns, which contribute to species intra- and interspecific interactions. Aiming to describe spatial patterns of species at fine spatial scales, we applied the quantitative analyses based on the relationships of nearest neighbors of conspecific and heterospecific trees. In a two-hectare plot of a tropical broadleaved forest stand in central Vietnam with minimal human influence, all tree individuals with diameter at breast height ≥ 2.5 cm were mapped and their characteristics were recorded. We applied two different types of analyses: (1) Intraspecific structural characteristics using nearest neighbor statistics; (2) overall interspecific associations through a classification scheme based on bivariate nearest neighbor distribution function D₁₂(r) and Ripley’s K function K₁₂(r). The findings showed that: (1) Most of studied species in the forest were highly mixed with other species, while conspecifics were regular to aggregated distribution at small spatial scales. Tree individuals with different diameter values were surrounded by heterospecific trees; (2) The majority of 306 species-species pairs showed spatial independence (66.7%), whereas 29.8% of all species showed an overall positive association and negative association consisted only a small percentage (3.5%) up to spatial scales of 50 m. We found significant evidences of the main ecological theories such as dispersal limitation, Neutral theory, Janzen-Connell hypothesis, and other effects like the stochastic dilution. We suggest using both the bivariate distribution of the structural parameters and the spatial point pattern analysis based on nearest neighbor distance as advantageous approaches for further understanding of population structure, as well as discovering and protecting biodiversity in the future.

The configuration of trees and their interplay offer vital perspectives into a forest community’s spatial structure and plant species’ coexistence mechanisms. This study aimed to investigate the spatial patterns and interactions of woody plant species in an evergreen broadleaved forest on the Con Dao Islands, Vietnam. A 4-ha study plot was established in 2022, and all trees with a diameter breast height (DBH) ≥ 5 cm were measured, identified species, and mapped. The spatial point pattern analysis method was employed to explore the spatial distribution and interactions of woody plant species in the study plot. The findings indicated that saplings (DBH < 10 cm) were mainly aggregated at a small scale of 0–10 m, whereas intermediate (10 cm ≤ DBH ≤ 20 cm) and adult (DBH > 20 cm) trees were randomly distributed. Species-area relationships and spatial patterns varied according to the life-history stages of each species and spatial scales. The results also suggested that species coexistence within the plant community was achieved through the overall effects of the diversity accumulator species, diversity repeller species, and neutral species. The ecological niche theory, unified neutral theory, and asymmetric competition principle were deemed appropriate for explaining the coexistence of woody plant species in the evergreen broadleaved forest on Con Dao Islands, Vietnam.