Sundarbans wetlands
The Sundarbans wetlands are among the largest contiguous tidal mangrove forests in the world, spanning over 2,510 square miles (6,500 square kilometers) across Bangladesh and India. Situated on the Ganges-Brahmaputra-Meghna delta along the Bay of Bengal, this unique ecosystem features a humid tropical climate with significant rainfall concentrated during the monsoon months. The Sundarbans is renowned for its rich biodiversity, supporting numerous species, including the Bengal tiger, Ganges river dolphin, saltwater crocodile, and hundreds of bird and fish species.
The region's mangrove trees, particularly the sundari and gewa species, play critical roles in erosion prevention and provide essential resources for local communities. However, the area faces significant challenges due to human activities such as fishing, logging, and agriculture, as well as climate-related threats like cyclones and rising sea levels. Conservation efforts, including the establishment of the Sundarbans National Park and its designation as a UNESCO World Heritage Site, aim to protect this vital ecosystem. Despite these initiatives, ongoing habitat loss and the impacts of human population pressures continue to pose substantial risks to the Sundarbans' ecological integrity.
Subject Terms
Sundarbans wetlands
Category: Marine and Oceanic Biomes.
Geographic Location: Asia.
Summary: Characterized by one of the world’s largest tidal mangrove forests, the Sundarbans wetlands is a biodiversity hot spot under threat from sea-level rise.
The Sundarbans—beautiful forests in Bengali—is among the world’s largest contiguous tidal mangrove forests. The biome covers more than 2,510 square miles (6,500 square kilometers), split between Bangladesh (62 percent) and India (38 percent). The Sundarbans is located on the vast Ganges-Brahmaputra-Meghna alluvial delta on the Bay of Bengal, a lush and extensive low-lying coastal area.
The climate here is humid tropical, with monsoon effects. Average temperatures are in the range of 70–86 degrees F (21–30 degrees C). Rainfall totals some 65–79 inches (1,640–2,000 millimeters) yearly. Most precipitation occurs in the May-to-October monsoon season, with heavier rain tending to fall in the eastern areas of the biome. Major storms often bring massive inundation, erosion-causing storm surges, and tidal waves.
Biodiversity
The Sundarbans wetlands form a coastal biodiversity hot spot, supporting 40 mammal species, with such hallmark species as the Ganges river dolphin (Platanista gangetica gangetica); 35 reptile species, including the saltwater crocodile (Crocodylus porosus); almost 300 species of birds, many migratory; 400 fish species; and almost 30 species of mangrove trees.
The mangrove types of sundari (Heritiera fomes) and gewa (Excoecaria agallocha) are the dominant tree species here. The former is an exceptionally good hardwood used in furniture, flooring, and boatbuilding, and it is a strong erosion-preventer in its tidal environment, while the latter is used for more mundane commercial functions such as making paper pulp and charcoal—but it also has a growing number of medicinal uses.
The vegetation community of the Sundarbans Wetlands biome also includes Avicennia spp., Sonneratia apetala, Bruguiera gymnorrhiza, Aegiceras corniculatum, and Rhizophora mucronata. The golpata palm Nypa fruticans is distributed throughout the ecosystem; its dense root system, underground stem, trunkless structure, and moderate salt-tolerance are extremely well-adapted to this wetland habitat. Dozens of types of grass, reed, and sedge are found here, as well.
The Sundarbans is perhaps most renowned for its population of Bengal tigers (Panthera tigris), thought to be the only tiger population in the world adapted to living within mangrove forests. The presence of large fauna and increasing human population densities in the Sundarbans mean that human-tiger conflicts are an important social issue. An average of 57 people per year were killed by tiger attacks between 1975 and 1984. One step to help both the tiger and the people has been the establishment of the Sundarbans National Park and Tiger Reserve, a major conservation area that comprises some 1,000 square miles (2,585 square kilometers) in the Indian portion of the biome.
Another mammal that benefits from the sanctuary of the reserve is the muntjac or barking deer (Muntiacus muntjak). Reptiles sheltering here include the northern river terrapin (Batagur baska), olive ridley sea turtle (Lepidochelys olivacea), water monitor (Varanus salvator), saltwater crocodile (Crocodylus porosus), and king cobra (Ophiophagus hannah). Amphibians found either here or in the Bangladesh portion of the Sundarbans include the tree frog (Polypedates maculatus), skipper frog (Euphlyctis cyanophylctis), and green frog (E. hexadactylus). The Sundarbans wetlands is rife with such crustaceans as fiddler crab (Uca spp.), shrimp (Penaeus monodon, Metapenaeus monoceros), and mangrove mud crab (Scylla serrata). Hundreds of spider species have also been identified here.
Birds flock here by the millions. Nine species of kingfisher, multiple types of sand piper, many varieties of heron, stork, tern, curlew, and at least 20 raptor species, including the sea eagle, rank among the most abundant.
Human Impacts
Tens of millions of people live in and not far upstream from the Sundarbans wetlands. Among the leading activities that most impinge upon the biota here are fishing, aquaculture, logging, and agriculture. Despite great exposure to the life-threatening dangers of major cyclones, many people live and work here—sometimes by their actions undermining the very protections against storm surge and flooding that the wetlands and their mangrove forests provide. It is far from a static situation: Cyclone Sidr in 2007 detrimentally affected 30 percent of the Sundarbans, while Cyclone Aila in 2009 destroyed up to 15 percent of the mangrove forest. In May 2020, Cyclone Amphan damaged more than 463 square miles (1,200 square kilometers) of the region’s mangroves.
Sea-level rise is expected to significantly threaten the flora and fauna of the Sundarbans during this century. Most of the Sundarbans is less than 3 feet (1 meter) above sea level; a rise of 11 inches (280 millimeters)—a conservative estimate of sea-level rise by 2100—is predicted to result in nonviable tiger populations in the Bangladeshi portion of the Sundarbans, as habitat is drowned and fragments of the small remaining mangrove patches will be unable to support breeding pairs. A 2016 study published in the journal Climatic Change estimated that by the year 2100, the Sundarbans wetlands may lose between a 31 square miles (81 square kilometers) and 538 square miles (1,393 square kilometers) of mangrove area.
Conservation Efforts
The ecological and socioeconomic functions of the Sundarbans, and the significant threats this ecosystem faces, mean that protecting this ecosystem is important. In 2019, the wetlands were named a Wetland of International Importance by the Ramsar Convention, making them the largest protected wetlands region in India.
The Sundarbans as a whole is listed as a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Natural Heritage Site. Remote sensing via satellite shows that, while the various forms of protective status has held down overall habitat loss in the Sundarbans over the past half-century, there has still been significant land-cover conversion, such as from mangrove to open water and barren land and mud flats.
Stepped-up protection measures include augmented patrols and enforcement, more strict permit requirements for the extraction of various products, and restricted extraction at identified key breeding grounds of certain animals. An Integrated Resource Management Plan (IRMP) was prepared in 1998 to sustainably manage the extraction of timber and nontimber products here. However, there is uncertainty as to whether the IRMP has been successful.
Bibliography
Bhargava, Radhika, and Daniel A. Friess. “Previous Shoreline Dynamics Determine Future Susceptibility to Cyclone Impact in the Sundarban Mangrove Forest.” Frontiers in Marine Science, 11 Mar. 2022, doi.org/10.3389/fmars.2022.814577. Accessed 31 Aug. 2022.
Banerjee, Anuradha. Environment, Population and Human Settlements of Sundarban Delta. New Delhi, India: Ashok Kumar Mittal, 1998.
Ghosh, Sahana. “Sundarban Reserve Forest now a Wetland of International Importance.” Mongabay-India, 6 Feb. 2019, india.mongabay.com/2019/02/sundarban-reserve-forest-now-a-wetland-of-international-importance/. Accessed 31 Aug. 2022.
Giri, Chandra, Bruce Pengra, Zhiliang Zhu, Ashbindu Singh, and Larry Tieszen. “Monitoring Mangrove Forest Dynamics of the Sundarbans in Bangladesh and India Using Multi-Temporal Satellite Data From 1973 to 2000.” Estuarine, Coastal and Shelf Science 73 (2007).
Iftekhar, M. S. and P. Saenger. “Vegetation Dynamics in the Bangladesh Sundarbans Mangroves: A Review of Forest Inventories.” Wetland Ecology and Management 16 (2008).
Loucks, Colby, Shannon Barber-Meyer, M. D. A. Hossain, Adam Barlow, and Ruhul M. Chowdhury. “Sea-Level Rise and Tigers: Predicted Impacts to Bangladesh’s Sundarban Mangroves.” Climatic Change 98 (2010).
Payo, Andres, et. al. “Projected Changes in Area of the Sundarban Mangrove Forest in Bangladesh Due to SLR by 2100.” Climatic Change, vol. 132, no. 2, 2016, pp. 279–291, doi: 10.1007/s10584-016-1769-z. Accessed 31 Aug. 2022.