Diversity and structural composition of species in dipterocarp forests: a study from Fasiakhali Wildlife Sanctuary,Bangladesh

Fasiakhali Wildlife Sanctuary is a protected area composed of tropical remnant rainforest that harbor substantial number of large, old Garjan (Dipterocarpus spp.) trees. The present study assessed composition, structure and diversity of the species in this protected area. A total of 32 trees species were recorded with DBH ≥ 11 cm belonging to 24 genera and 19 families. The forest is low in plant diversity as represented by Shannon–Wiener diversity and Simpson Dominance indices. Dipterocarpus turbinatus was the most dominant species with maximum relative density, frequency, dominance, and importance value index. Syzygium firmum and Tectona grandis followed in terms of dominance. The structural composition indicated higher number of individuals in the medium growth classes (41 to < 511 cm DBH and 16–20 m height ranges), whereas D. turbinatus was the only species that dominated most of the growth classes. Poor stem density in lower growth classes indicated meager recruitment of regeneration which may be due to lower annual precipitation, increased grazing and encroachments. This study will help to understand the patterns of tree species composition and diversity in the remnant dipterocarp forests of Bangladesh. It will also contribute to identifying threatened plants to undertake D. turbinatus based conservation and sustainable management of the Fasiakhali Wildlife Sanctuary.