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.

Although woody plant encroachment of tropical forest ecosystems has been related to altered disturbance regimes, its impacts on the nearest neighborhood structures and community phylogenetics are still poorly understood. Streblus macrophyllus is a light-demanding species during its early life stages and is shade-tolerant as a mature tree. S. macrophyllus can be found in tropical karst evergreen forests in northern Vietnam. It often regenerates at high densities in anthropogenic disturbed forest stands. To understand the structural patterns of disturbed forests encroached by S. macrophyllus at different abundance levels, three fully mapped 1-ha plots were established in Cuc Phuong National Park. Methods considering the phylogenetic community and nearest neighbor statistics were applied to identify how community structure changes during S. macrophyllus encroachment. Results showed that phylogenetic distance, phylogenetic diversity, and mean phylogenetic distance increased when species diversity increased and the abundance of S. macrophyllus decreased in forest communities. Net related index values were positive, which indicates a clustered phylogenetic structure among all sampled forest communities. S. macrophyllus trees were mixed well with heterospecifics and had regular to aggregated distributions, whereas the species showed evidence of being a strong competitor with its neighbors. Competition could be a major ecological process regulating forest communities encroached by S. macrophyllus. According to the forest disturbance effects, phylogenetic community properties showed the loss of phylogenetic relatedness when S. macrophyllus increased in abundance. To our knowledge, S. macrophyllus encroaches tropical rain forest communities as a disturbance-adapted species.

Degradation of tropical forests is a major driver of the global extinction crisis. A key question is understanding the role of evolution history during forest succession in the context of forest restoration for maintaining ecosystem function and stability. This study was conducted in a fragmented forest landscape in the central highlands of Vietnam. We sampled living trees with diameters at breast height of ≥6.0 cm in nineteen 0.25 ha plots to evaluate forest community structure changes over two early successional stages (<10 years and 10–20 years old) after abandonment and old-growth. We used both statistically metric and nonmetric analyses to examine correlations of community composition during successional stages and along elevational gradients. We found that (i) significant differences existed in the structural compositions between early successional forests and old-growth forests, but did not exist within early successional forests; (ii) the phylogenetic structure shifted from overdispersion to clustering with increasing successional ages; and (iii) above-ground biomass (AGB), representing ecosystem functioning, significantly increased from early-to-late successional stages, but did not correlate with phylogenetic diversity or elevation. Our results revealed that the forest community structure was strongly affected by degradation, particularly AGB and phylogenetic structure. These findings have clear implications for sustaining biodiversity persistence and ecosystem functioning in human-modified landscapes in the study region.

The study of ecological species groups (ESGs) and interspecific interactions offers important insights into the mechanisms that drive tree species coexistence and enhances our understanding of plant community structure, function, and taxonomy. This study aimed to identify ESGs within a seasonal tropical forest in Phou Khao Khouay National Park, located in central Laos, and to investigate the key environmental factors influencing their distribution. Additionally, the study analysed community stability and interspecific associations among woody species using various statistical techniques, including Variance Ratio (VR), chi-squared tests, Association Coefficients (AC), and percentage of Co-occurrence (PC). To collect data, thirty-two permanent plots, each covering an area of 2500 m² (50 × 50 m), were established. In each plot, floristic data and species abundance were recorded, along with soil samples from two depths (0–10 cm and 10–20 cm) for physicochemical analysis. Vegetation data were classified using Two-Way Indicator Species Analysis (TWINSPAN), and differences between ESGs were evaluated using Analysis of Variance (ANOVA). Indicator Species Analysis (ISA) was applied to identify key species for each ESG, while Canonical Correspondence Analysis (CCA) was employed to explore the relationships between ESGs and environmental variables. The results revealed that the woody plant communities in the study area were relatively stable, exhibiting predominantly positive interspecific associations. Additionally, the distribution of the fosur identified ESGs showed a strong correlation with topographical factors – such as elevation, aspect, and slope – and soil properties, including pH, organic matter content, cation exchange capacity, total nitrogen, phosphorus, potassium, and soil texture. These findings underscore the importance of recognizing microhabitats that support the growth and conservation of woody plant species in Phou Khao Khouay National Park, offering valuable insights for future ecological research and conservation initiatives.