Structural complexity and tree species composition of mangrove forests of the Andaman Islands, India

This study reports the mapping, structural characteristics and distribution of mangrove species of the Andaman Islands. 79 mangrove patches were identified using Thiessen polygons of which, 53 accessible patches were surveyed during 2014-2015. Multiple linear transects were laid at each of the mangrove patches and data pertaining to diameter at breast height, basal area and height were recorded for all mangrove trees within a 10 x 10 m quadrat laid along the transects at 50 m intervals. Altogether, 178 quadrats were laid and 25 mangrove species representing 11 families and 14 genera were recorded. Of the 3073 mangrove plants enumerated in the present study, 96.06% were composed of trees (> 4 m height), 1.99% of saplings (> 1 m to 4 m height) and 1.95% of seedlings (1 m height). The number of species per quadrat ranged from 1 to 9 and majority of the quadrats had 2-3 species. Density and basal area of mangrove trees ranged from 1252 ha(-1) to 2200 ha(-1) and 30.8 m(2)/ha to 59.6 m(2)/ha, respectively. High diversity indices (Shannon-Wiener index ranged from 1.65 to 2.24; Simpson index from 0.74 to 0.85 and Pielou's evenness index from 0.66 to 0.84) indicated greater diversity and even dispersion of mangroves in the Islands. The study also revealed that the mangrove forests of Andaman Islands were characterized by a mixed species composition. Most of the sites were represented by different combinations of dominant and co-dominant species, all from the family Rhizophoraceae. The present study highlights the need for conserving the mixed species mangrove forests of Andaman and Nicobar Islands and development of location-specific management plans for biodiversity conservation.