Mangrove species diversity, stand structure and zonation pattern in relation to environmental factors — A case study at Sundarban delta, east coast of India

The forest structure and its relation to environmental parameters of Sundarbans, largest mangrove habitat in India, are presented. Quadrat method was used to analyze the vegetation-environment interaction and structural maturity of mangroves. Floristic studies revealed twenty-seven mangrove species including the critically endangered Sonneratia griffithii and endangered Heritiera fomes. Based on Importance Value Index, Avicennia marina, Excoecaria agallocha, Avicennia officinalis and Avicennia alba were designated as the most important species. Higher diversity indices were observed (Shannon index, ranged from 4.2-1.8; Pielou’s index, 0.96-0.91) revealing greater species diversity and even dispersion of mangroves in Sundarbans. Stem density varied from 133 to 19333 ha−1 and individual basal area 0.4 to 13.4m2ha−1. A very low Maturity Index Value was recorded indicating a low degree of structural maturity. Most of the vegetation parameters (density, species diversity index, β diversity) and few of the edaphic parameters (pH, grain size, total carbon) were found to be in better condition; however, salinity showed significant negative correlations with vegetation characteristics. The study revealed a mixed species composition with intermediate structural development indicating a growing forest in Sundarbans. The data evolved in the study would be fundamental in site-specific management and conservation efforts of mangroves in this world heritage site.