Ecological species groups and interspecific associations of dominant woody species in a seasonal tropical forest of Laos

Abstract

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.