Growth Performance of Exotic and Indigenous Tree Species Across Site Conditions in a Subtropical Hill Ecosystem

Subtropical hill forests play vital roles in biodiversity, climate regulation, and soil stability. However, unsustainable land use and logging have caused soil degradation, threatening these ecosystems and hindering reforestation. Effective restoration requires selecting tree species suited to site conditions, but knowledge of native and exotic species performance across altitudinal gradients remains limited. To address this knowledge gap, this study aimed to evaluate the growth and survival of native and exotic tree species planted at three altitudinal zones (bottom hill: up to 25 m, middle hill: 25–45 m, and top hill: above 45 m mean sea level) within the Chittagong University campus hill ecosystem. Using systematic random sampling, 59 plots (20 m × 20 m) containing 886 trees representing 21 species were assessed for height, diameter at breast height (DBH), and survival at plantation ages ranging from 5 to 35 years. Species were categorized into short-rotation and medium-to-long rotation groups to analyze species-site interactions. Results demonstrated superior growth of Gmelina arborea at the top hill among short-rotation species, while native long-rotation species such as Dipterocarpus turbinatus and Elaeocarpus serratus showed maximum height and DBH at higher altitudes. Survival rates were significantly lower at the middle hill, correlating with frequent illegal felling, while top and bottom hills showed better species establishment. The findings highlight the critical importance of species-site matching and suggest that anthropogenic disturbances are a major constraint on reforestation success in subtropical hill forests. This study provides valuable empirical data to inform species selection and forest management strategies, ultimately supporting more sustainable afforestation efforts and ecosystem restoration in similar subtropical hill regions globally.