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Southern Asia: Western Bangladesh into India

The Sundarbans Freshwater Swamp Forests [IM0162] ecoregion is nearly extinct. Hundreds of years of habitation and exploitation by one of the world's densest human populations have exacted a heavy toll of this ecoregion's habitat and biodiversity. Because it sits in the vast, productive delta of the Ganges and Brahmaputra rivers, the annual alluvial deposits make the ecoregion exceptionally productive. Therefore, most of the natural habitat has long been converted to agriculture, making it almost impossible to even surmise the original composition of the ecoregion's biodiversity.

  • Scientific Code
  • Ecoregion Category
  • Size
    5,600 square miles
  • Status
  • Habitats

Location and General Description
This ecoregion represents the brackish swamp forests that lie behind the Sundarbans Mangroves [IM1406] where the salinity is more pronounced. The freshwater ecoregion is an area where the water is only slightly brackish and becomes quite fresh during the rainy season, when the freshwater plumes from the Ganges and Brahmaputra rivers push the intruding salt water out and also bring a deposit of silt (Champion and Seth 1968). Like the vast mangrove ecoregion, the freshwater swamp forest ecoregion also straddles the boundary between Bangladesh and India's state of West Bengal.

The June to September southwest monsoon brings heavy rains. Frequent, devastating cyclones also sweep in from the Bay of Bengal, causing widespread destruction. Annual rainfall can exceed 3,500 mm, and the daytime temperatures can rise above 48(C during these monsoon months, which when coupled with the humidity can be unbearable.

Habitat loss is so extensive, and the remaining habitat is so fragmented, that it is difficult to ascertain the composition of the original vegetation of this ecoregion. According to Champion and Seth (1968), the freshwater swamp forests are characterized by Heritiera minor, Xylocarpus molluccensis, Bruguiera conjugata, Sonneratia apetala, Avicennia officinalis, and Sonneratia caseolaris, with Pandanus tectorius, Hibiscus tiliaceus, and Nipa fruticans along the fringing banks (Champion and Seth 1968).

Biodiversity Features
This ecoregion, together with the mangrove ecoregion, is an important refuge for the tiger (Panthera tigris). It is especially important to conserve tigers that are behaviorally and ecologically adapted to mangrove and swamp habitats. The known mammal fauna includes fifty-five species, but none are endemic to the ecoregion. In addition to the endangered tiger, there are several other threatened mammal species, such as the capped langur (Semnopithecus pileatus), smooth-coated otter (Lutrogale perspicillata), Oriental small-clawed otter (Aonyx cinerea), and great Indian civet (Viverra zibetha). The ecoregion also contains the leopard (Panthera pardus) and several smaller predators such as the jungle cat (Felis chaus), fishing cat (Prionailurus viverrinus), and leopard cat (Prionailurus bengalensis).

About 190 bird species have been recorded from the ecoregion. None are endemic, but the osprey (Pandion haliaetus) and grey-headed fish-eagle (Ichthyophaga ichthyaetus) should be focal species because of their role as predators in this ecosystem that includes a significant aquatic component.

Conservation activities in the aquatic habitat should also include the Gangetic dolphin (Platanista gangetica) and the three crocodile species that co-occur here: the marsh crocodile or mugger (Crocodylus palustris), estuarine crocodile (Crocodylus porosus), and gharial (Ghavialis gangeticus).

Current Status
This ecoregion is nearly extinct, the victim of large-scale clearing and settlement to support one of the densest human populations in Asia. There are two protected areas that cover a mere 130 km2 of the ecoregion (table 1).

Table 1. WCMC (1997) Protected Areas That Overlap with the Ecoregion.

Protected Area Area (km2) IUCN Category
Narendrapur 110 IV
Ata Danga Baor WS 20  
Total 130  

Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

Types and Severity of Threats
The large human population that has settled in this ecoregion and used its resources for hundreds of years has exacted a heavy toll on the natural habitat. Very little of the natural habitat of this ecoregion now remains, and even the remaining fragments are degraded.

Illegal hunting and habitat loss have caused several local extinctions of key species such as swamp deer (Cervus duvaucelii). Others, such as the gharial, are on the brink of extinction. The tiger is severely threatened.

Oil spills from the ships that travel up the river to the large port city of Calcutta and pollution from large settlement and developments-a proposed fertilizer plant is one example-rank among some of the other significant threats.

The diversion of more than a third of the Ganges's dry-season flow through the Farraka Barrage in India will also affect water flows. Changes to the water flows will be especially critical to this ecoregion because the vegetation characteristics here depend on salinity levels.

Justification of Ecoregion Delineation
We used MacKinnon's (1997) digital map of the original habitat to identify the boundaries of this ecoregion. In keeping with our rules for defining ecoregions, we separated the freshwater swamp forests from the mangroves in the Ganges River delta and placed them in their own ecoregion, the Sundarbans Freshwater Swamp Forests [IM0162]. This ecoregion falls within Udvardy's Bengalian rain forest biogeographic province.

References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List

Prepared by: Gopal S. Rawat and Eric D. Wikramanayake
Reviewed by: