Spatial Distribution Patterns and Competitions of Dominant Tree Species in an Evergreen Broadleaved Forest of Bidoup-Nui Ba National Park, Southern Vietnam

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Abstract Understanding the mechanisms driving species coexistence is fundamental to forest ecology. Processes such as dispersal limitation, habitat heterogeneity, and plant-plant interactions shape the spatial patterns and dynamics of forest communities. This study investigated intra- and interspecific competition and spatial distribution patterns of dominant tree species in the evergreen broadleaved forest of Bidoup-Nui Ba National Park, southern Vietnam. A 4-ha study plot was established within the strictly protected zone of the national park. All trees with a diameter at breast height (DBH) ≥ 2.5 cm were mapped and surveyed. The survey included species identification, DBH measurements, and categorization of trees into three life-history stages: juvenile (DBH < 5 cm), subadult (5 cm ≤ DBH < 15 cm), and adult (DBH ≥ 15 cm). The Hegyi competition index and univariate pair-correlation function were used to assess neighborhood competition and spatial distribution. The study recorded 66 tree species, with six species (Castanopsis echinocarpa, Polyosma nhatrangensis, Syzygium oblatum, Syzygium rubicundum, Craibiodendron stellatum, and Lithocarpus coinhensis) identified as dominant based on their importance value index. These species exhibited reverse J-shaped DBH distributions, indicating strong regeneration capacity. Spatial distribution analyses showed that the six dominant species exhibited aggregated patterns at small spatial scales (r < 15 m) and random patterns at larger spatial scales (r > 15 m). Interspecific competition exceeded intraspecific competition, with juvenile and subadult trees experiencing greater competitive pressures than adults. Tree size, life-history stage, and spatial scale significantly influenced competition dynamics and spatial patterns. Processes such as dispersal limitation, self-thinning, and habitat heterogeneity played key roles in shaping the observed patterns. This study provides insights into the spatial ecology and competitive interactions of dominant tree species, contributing to a deeper understanding of species coexistence. The findings support conservation efforts and inform sustainable forest management in Bidoup-Nui Ba National Park and similar ecosystems.

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