Abstract <p>Plants are sessile organisms, and their survival is closely intertwined with ecological and evolutionary processes. Therefore, understanding the mechanisms that underpin plant diversity in tropical forests is critically important. This study utilized the individual species-area relationship model in conjunction with six species-abundance models—including the Zipf-Mandelbrot, Log-normal, Niche-preemption, Broken-stick, Zero-sum polynomial, and Volkov models—to explore the mechanisms that facilitate the coexistence of woody species. Data was collected from a 4-ha study plot established within an evergreen broadleaved forest in the Con Dao archipelago in Ba Ria–Vung Tau Province, southern Vietnam. Our findings revealed that diversity-accumulation species and neutral species significantly influence the local diversity structure of tree species, although their relative importance varies across spatial scales. Specifically, the Niche-preemption model best explains species coexistence at a sampling scale of 10 × 10 m, while the Volkov model is more applicable at large sampling scales of 80 × 80 m and 100 × 100 m. Deterministic processes—such as plant-plant interactions, negative density dependence, and habitat heterogeneity—are the primary drivers of species coexistence at small spatial scales (0–10 m). Conversely, stochastic processes, including seed dispersal and ecological drift, are predicted to play a crucial role in maintaining species coexistence at large spatial scales (10–50 m).</p>