Diversity and population structure of tree species in a protected area on the southeastern coast of Bangladesh

Inani National Park (INP) is a protected area supporting a variety of threatened and endangered species. However, anthropogenic pressures, including of Rohingya refugees’ influx into the Cox’s Bazar, have imposed significant stress on its forest ecosystems. This study assessed the composition, structure, and diversity of INP’s forests to provide a scientific foundation for conservation and sustainable management. Stratified random sampling was conducted across four forest strata: Shrub with Scattered Trees, Hill Forest, Forest Plantation, and Others. Across 131 sampling plots (0.1134 ha each), 455 trees representing 66 species and 33 families were recorded. Fabaceae was the most species-rich family, comprising 10 species. Tree density averaged 30.62 trees ha−1, with the Forest Plantation exhibiting the highest density (99.51 trees ha−1) and Hill Forest the lowest (17.63 trees ha−1). Areca catechu dominated with 28.35% relative density 40.49 IVI. Diversity indices indicated a moderately diverse ecosystem with heterogeneous species distribution. The Shannon–Wiener index was highest in the Shrub with Scattered Trees stratum (H = 3.572), while Simpson’s index (D = 0.89) reflected high species diversity and calculated canopy cover, averaging 45.19%. Despite its ecological significance, INP has experienced substantial disturbances, resulting in 2500 ha forest loss. Acacia auriculiformis, Mangifera indica, Areca catechu, Artocarpus heterophyllus, and Cocos nucifera were the key indicator species, with the ten families and genera by species richness comprising 59.09% and 27.27% of all recorded individuals. The presence of invasive Acacia auriculiformis, indicates ecological imbalance and need for restoration interventions. These findings provide critical insights to guide biodiversity conservation and enhance INP’s forest ecosystems resilience.