8/13/2012

Les Sundarbans, Site Naturel exceptionnel (Bangladesh)

La forêt de mangroves des Sundarbans, l’une des plus grandes forêts mondiales de ce type (140 000 ha), couvre le delta du Gange, du Brahmapoutre et de la Meghna, dans la baie du Bengale. Elle est contiguë au site indien des Sundarbans, classé patrimoine mondial depuis 1987. L’ensemble du site est entrecoupé d’un réseau complexe de voies d’eau sous l’influence des marées, de vasières et d’îlots de forêts de mangroves halophiles, offrant un excellent exemple de processus géologiques en cours. Le site est également connu pour la richesse de sa faune qui comprend 260 espèces d’oiseaux, le tigre du Bengale et d’autres espèces menacées comme le crocodile marin et le python indien. 

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The Sundarbans consist of three wildlife sanctuaries (Sundarbans West, East and South) lying 
on disjunct deltaic islands just west of the main outflow of the Ganges, Brahmaputra and Meghna rivers, close to the border with India.
The sanctuaries are intersected by a complex network of tidal waterways, mud flats and small islands of salt tolerant mangrove forests. The area is flooded with brackish water during high tides which mix with freshwater from inland rivers.
The larger channels are often a kilometre or two wide and generally run in a north-south direction. Rivers tend to be long and straight, a consequence of the strong tidal forces and the easily eroded clay and silt deposits. But apart from Baleswar River the waterways carry little freshwater as they are cut off from the Ganges, the outflow of which has shifted from the Hooghly-Bhagirathi channels in India progressively eastwards since the 17th century. They are kept open largely by the diurnal tidal flow.
Alluvial deposits are geologically very recent and deep. The soil is a clay loam with alternate layers of clay, silt and sand. The surface is clay except on the seaward side of islands in the coastal limits, where sandy beaches occur. The monsoon rains, flooding, delta formation, and tidal influence combine in the Sundarbans to for a dynamic landscape that is constantly changing.
Sands collect at the river mouths and form banks and chars, which are blown into dunes by the strong south-west monsoon winds. Finer silts are washed out into the Bay of Bengal where they form mud flats in the lee of the dunes. These become overlain with sand from the dunes and develop into grassy middens.
Because of the dominance of saline conditions, the forest flora in the western Sundarbans is not as diverse as in the east. Forest areas are dominated by a few species mostly Sundri and Gewu and patches of Nypa palm and several other of the 27 species of mangrove that are found in the Sundarbans.
The property is the only remaining habitat in the lower Bengal Basin for a variety of faunal species. The presence of 49 mammal species has been documented. Of these, no less than five spectacular species, Javan rhinoceros, water buffalo, swamp deer, gaur and probably hog deer have become locally extirpated since the beginning of the 21st century.
The Sundarbans of Bangladesh and India support one of the largest populations of Royal Bengal Tiger with an estimated 350 individuals. Other mammals include spotted deer and wild boar, three species of wild cat and Ganges River dolphin, which occurs in some of the larger waterways. Of the three species of otter, smooth-coated otter is domesticated by fishermen and used to drive fish into their nets.
Some 53 reptile species and eight amphibian species have been recorded of these mugger crocodile is now extinct, probably as a result of past over-exploitation, although it still occurs in at least one location nearby. Estuarine crocodile still survives but its numbers have been greatly depleted through hunting and trapping for skins. Four species of marine turtle have been recorded from the area. The varied and colourful bird-life to be seen along its waterways is one of the Sundarbans' greatest attractions. There are some 315 species of waterfowl, raptors and forest birds including nine species of kingfisher and the magnificent white-bellied sea eagle.
Source : whc.unesco.org