Abstract

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Estuarine salinification has been suggested a serious threat to the survival and growth of mangroves. However, there are few fine-scale temporal and spatial data set of Above Ground Biomass (AGB) of mangrove species in relation to aquatic salinity which can provide a base line definition of extant conditions. Here we provide observational data from 24 different sites in the estuarine regions of Indian Sundarbans that is a luxuriant habitat for mangroves. Three distinct sectors within this habitat differ by salinity and to some extent by the nature of substratum. The influence of salinity is highly species-specific. Hence, we have focussed on the AGB of Sonneratia apetala in these three sectors of Indian Sundarbans namely western, central and eastern sectors. In the western sector, the average AGB of the species was 36.85 t ha^-1 in 1996, while in 2005 and 2015 the mean AGB were 43.17 t ha^-1 and 49.04 t ha^-1 respectively. In the central sector, the mean AGB of the species varied as per the order 7.83 t ha^-1 (in 2015) > 2.74 t ha^-1 (2005) > 0.84 t ha^-1 (1996). The eastern sector of Indian Sundarbans adjacent to Bangladesh Sundarbans exhibited highest AGB in 2015 (mean value = 20.21 t ha^-1) followed by 2005 (mean value = 14.72 t ha^-1) and 1996 (mean value = 9.16 t ha^-1). In selected sectors the significant variation in AGB may be related to pronounced spatio-temporal variations of salinity. It is noted that S. apetala grows well in hyposaline environment compared to hypersaline central Indian Sundarbans. The study thus concludes with the lesson that salinity profile must be taken into account while developing the master plan for afforestation programme in this deltaic ecosystem at the apex of Bay of Bengal.

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