Canopy gaps influence regeneration dynamics in cyclone affected mangrove stands in medium saline zone of the Sundarbans, Bangladesh

Abstract

Regeneration in the canopy gaps in medium saline zone of the Sundarbans Reserve Forest (SRF), Bangladesh was studied to investigate either significant floristic and structural differences between canopy gaps and adjacent forest with continuous canopy. A total of eighteen plots (30 m × 20 m) with an area of 1.08 ha were sampled from six sites (three sample plots from each sites). Species richness in terms of total number of species (seedling, height < 1.5 m) in the study area was not significantly different between canopy gaps and continuous canopy, but there was still difference in floristic composition. Heritiera fomes and Excoecaria agallocha were the dominant and co-dominant seedling species in both sites but the study demonstrated that Ceriops decanrda, Aegiceras corniculatum and Phoenix paludosa were restricted only in canopy gaps whereas Bruguiera sexangula, Brownlowia tersa, Cerbera manghas and Petunga roxburghii were restricted only in continuous canopy. The study also revealed significant difference of seedling density between gaps (43,454 ha−1) and continuous canopy (28,237 ha−1). The density of H. fomes was significantly higher in canopy gaps (38,952 ha−1) than under continuous canopy (15,298 ha−1). Shannon diversity index (0.41 in gaps and 0.82 in canopy) was significantly reduced (50% of canopy) in the gaps. Our study concluded that canopy gaps enhanced colonization of H. fomes seedlings in the medium saline zone than does of floristic composition and species diversity. The study demonstrate that information on seedling dynamics in the canopy gaps may be important for management and conservation of the SRF.