Diversity, distribution and vegetative structure of mangroves of the Andaman and Nicobar Islands, India

The present study was carried out to determine the diversity, distribution and vegetative structure of mangroves of the Andaman and Nicobar Islands (ANI). The results suggest that mangroves of the ANI consist of 38 mangrove species belonging to 12 families and 19 genera, which includes 4 hybrids and 34 species. In other words, about 50% of the global mangrove species are present in ANI. Andaman Islands have 35 species and Nicobar Islands have 21 mangrove species. The average tree density in ANI is 1746/per hectare and varies from 487 to 2383 per hectare. The Shannon diversity index for the whole ANI is 2.94 and Simpson index is 0.07. Family Rhizophoraceae constitutes an important vegetative component in the mangroves of the ANI followed by Acanthaceae, Lythraceae and Malvaceae. Rhizophora spp. constitutes 19% of the Important Value Index (IVI) and R. apiculata is dominant in ANI. Among the eight forest divisions, mangrove diversity is high in South Andaman (30 species) followed by Middle Andaman (28), Mayabunder (25), Diglipur (25), Nicobar (21), Little Andaman (20), Havelock (20) and Baratang (20). The average mangrove plant density and Shannon diversity index (H') is high in Middle Andaman (2101/hectare; H' = 2.93). Species richness index (d') is high in South Andaman (3.32). Evenness index (J') is high in Little Andaman (0.92). Simpson dominance index (D) ranged between 0.07-0.1, and this agrees with the high diversity in mangroves of ANI. In all the divisions Rhizophora spp. constitutes a major vegetative component except, Diglipur and Nicobar. In Diglipur Bruguiera spp. are dominant, while in Nicobar Sonneratia spp. are dominant. The low similarity value of the Nicobar division with other divisions indicates the difference in floristic structure of mangroves of the Andaman Islands and Nicobar Islands. The present study also indicates that mangrove of ANI are more diverse in its species composition than the other mangrove habitats in India.