Advanced Land Observing Satellite Phased Array Type L-Band SAR (ALOS PALSAR) to Inform the Conservation of Mangroves: Sundarbans as a Case Study

William Cornforth,Nathalie Pettorelli,Temilola Fatoyinbo,Terri Freemantle

doi:10.3390/rs5010224

William Cornforth, Nathalie Pettorelli + Show 2 more

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https://doi.org/10.3390/rs5010224

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Abstract

Mangroves are an important bulkhead against climate change: they afford protection for coastal areas from tidal waves and cyclones, and are among the most carbon-rich forests in the tropics. As such, protection of mangroves is an urgent priority. This work provides some new information on patterns of degradation in the Sundarbans, the largest contiguous mangrove forest in the world, which are home to more than 35 reptile species, 120 commercial fish species, 300 bird species and 32 mammal species. Using radar imagery, we contrast and quantify the recent impacts of cyclone Sidr and anthropogenic degradation on this ecosystem. Our results, inferred from changes in radar backscatter, confirm already reported trends in coastline retreat for this region, with areas losing as much as 200 m of coast per year. They also suggest rapid changes in mangrove dynamics for Bangladesh and India, highlighting an overall decrease in mangrove health in the east side of the Sundarbans, and an overall increase in this parameter for the west side of the Sundarbans. As global environmental change takes its toll in this part of the world, more detailed, regular information on mangroves’ distribution and health is required: our study illustrates how different threats experienced by mangroves can be detected and mapped using radar-based information, to guide management action.

Highlights

Anthropogenic activities and their consequences, including climate change, are negatively impacting biodiversity and ecosystem services, with ecosystem loss and degradation occurring at an alarming rate [1]
Causes behind the reported patterns in degradation cannot be identified from our analysis, a variety of reasons including changing salinity, top-dying disease, storm surges, effects of climate change such as increased melt-water and changes in sea-level, and direct anthropogenic impacts such as redirection of freshwater, deforestation and oil-spills, have been previously associated with mangrove degradation in this region [8,37,45]
An assessment by Akhter and colleagues [32] based on a Principal Component Analysis of an ASTER image collected a few days after the cyclone struck suggested that approximately 22% of the Sundarbans was affected by cyclone Sidr, 11% of which was ‘highly affected’, whilst other studies estimated that between 19% and 31% of the Sundarbans’ mangroves was impacted by this extreme natural event [42,46,47]

Summary

Introduction

Anthropogenic activities and their consequences, including climate change, are negatively impacting biodiversity and ecosystem services, with ecosystem loss and degradation occurring at an alarming rate [1]. Mangroves are unique intertidal forested wetlands confined to tropical and subtropical coastal environments, supporting a diverse range of organisms that have developed unique adaptations by living at the interface between the terrestrial and marine biomes [2,3]. Their total area is estimated at 137,760 km globally [4], which equals only 0.1% of the earth’s continental surface. Mangroves provide societal and ecological goods and services, including food and sustenance, fuel, raw building materials for local populations, and safe breeding and nursing grounds for marine and pelagic species [7,8,9]

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