Differences in Seedling and Sapling Densities and Species Composition between Canopy Gaps and Forest Understories in a Subtropical Forest in Bangladesh

Canopy openings have a vital role in forest structure, regeneration, and plant composition. In this study, we investigated and compared the species composition and densities of seedlings and saplings between canopy gaps (openings) and forest understories (in dense canopies) in a sub-tropical forest of Bangladesh. We objectively identified 42 canopy openings between transect lines and 42 main plots in dense canopies, sampled for regeneration and young tree patterns. For the regeneration study, we placed 2 m×2 m four subplots in each canopy opening and the main plot of dense canopy, thus making a total of 336 subplots. The species diversity of seedlings, saplings, and trees were significantly (P≤0.05) higher in the dense canopy than in the canopy opening. Although, most dominant and frequent regenerating species such as Diospyros pilosula, Garcinia cowa, Brownlowia elata, and Lithocarpus polystachya were common in both dense canopy and openings, the canopy openings had the highest Importance Value Index, suggesting the significance of gap dynamics in the dominance of native floral species. The dense canopy played an important role in forest compositions because 12 regenerating species, including Stereospermum suaveolens and Diospyros montana, were not found in the canopy openings, implying that rain forests must maintain a high canopy cover for regeneration.