The influences of cyclone on abundance, species diversity and floristic composition in mangrove ecosystem in the Sundarbans, Bangladesh

Cyclones, an example of a catastrophic disturbance, are likely to cause substantial effects on floristic composition and stand structure of mangrove vegetation. CycloneSidr, a category-5 equivalent tropical cyclone passed over the Sundarbans, Bangladesh on November 2007. We assessed floristic composition, abundance and biodiversity in cyclone affected sites (CAS) and undisturbed sites (UDS) of a similar ecosystem to minimize the salinity effect on vegetation eight years after the effect of Cyclone Sidr. We have recorded a total 14 species (11 in UDS and 10 in CAS). Out of 14 only 7 species were common in both sites. Top 5 common species were Heritiera fomes, Excoecaria agallocha, Amoora cucullata, Cynometra ramiflora, and Intsia bijuga. Ceriops decandra, Phoenix paludosa, and Aegiceras corniculatum were found only in CAS, and Bruguiera sexangula, Petunga roxburghii, Cerbera manghas and Brownlowia tersa were found only in UDS. The study revealed that H. fomes (IV 65.29% in CAS and 49.77% in UDS) and E. agallocha (IV 16.3% in CAS and 22.19% in UDS) were the dominant and co-dominant species respectively in both sites. The study revealed that stand density (total individuals and seedlings) accelerated in CAS. However species richness, tree height and basal area of CAS showed closer resembles to UDS than does floristic composition and species diversity. The values of Shannon’s index H’ and Pielou’s index J’ of CAS were significantly lower than that of UDS due to tremendously high abundance of H. fomes in CAS. Despite closer resembles of species richness, tree height, basal area of CAS to UDS, the compositional similarity was only 67.4%. This study concludes that cyclone affected sites accelerated abundance rather than floristic composition and species diversity at the Sundarbans mangrove ecosystems.