Abstract
The Sundarbans, the largest mangrove ecosystem in the world, is under threat from historical and future human exploitation and sea level rise. Limited scientific knowledge on the spatial ecology of the mangroves in this world heritage ecosystem has been a major impediment to conservation efforts. Here, for the first time, we report on habitat suitability analyses and spatial density maps for the four most prominent mangrove species - Heritiera fomes, Excoecaria agallocha, Ceriops decandra and Xylocarpus mekongensis. Globally endangered H. fomes abundances declined as salinity increased. Responses to nutrients, elevation, and stem density varied between species. H. fomes and X. mekongensis preferred upstream habitats. E. agallocha and C. decandra preferred down-stream and mid-stream habitats. Historical harvesting had negative influences on H. fomes, C. decandra and X. mekongensis abundances. The established protected area network does not support the most suitable habitats of these threatened species. We therefore recommend a reconfiguration of the network to include these suitable habitats and ensure their immediate protection. These novel habitat insights and spatial predictions can form the basis for future forest studies and spatial conservation planning, and have implications for more effective conservation of the Sundarbans mangroves and the many other species that rely on them.
Highlights
The mangrove biome, spanning over 137,760 km[2] of coastal areas in 118 countries is under severe threat
Given the super-dominance of E. agallocha and H. fomes and tree structural complexities in the ecosystem which might have increased tree measurement errors, we initially considered two alternative measures of abundance: 1) density of all stems for each plot, and 2) total basal area for each plot as biotic variables
The most parsimonious generalized additive models38 (GAMs) for estimating species abundances explained the variability of H. fomes (68%), E. agallocha (84%), C. decandra (73%), and X. mekongensis (75%) (Table 2)
Summary
The mangrove biome, spanning over 137,760 km[2] of coastal areas in 118 countries is under severe threat. The Sundarbans stretches along the coast of Bangladesh (6,017 km2) and India (4,000 km2) and forms the largest single block of halophytic mangrove forest in the world. This unique ecosystem provides the breeding and nursing habitats for diverse marine organisms, houses the last habitats of many endangered animals eg. Royal Bengal tiger (Panthera tigris) and Ganges river dolphin (Platanista gangetica), supports the livelihoods of about 3.5 million coastal dwellers and helps reduce the death toll of tsunamis and cyclones[6] in the area It was designated a Ramsar site under the Ramsar Convention in 19927. Future climate scenarios (in particular for SLR) and ongoing habitat degradation may alter the current spatial distributions of these mangrove species and forest community composition
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