The Sundarbans

The Sundarbans

By dr.fourkan Ali

Overview of an amazing ecosystem

The Sundarbans is the world's single largest mangrove forest that extends across Bangladesh and the indian state of West Bengal. Centuries ago, people used to refer to the Sundarbans and its adjacent region as `Bhati’ - meaning low-lying areas -- which suggest that the most important physiographical feature around was its wetlands and wateroodies. Aunique reservoir of bio-diversity the forest is more than five thousand years old. There is no archeological evidence that could provide a reliable chronological history of the Sundarbans. Bangladesh owns about two thirds of the formt that makes about 45 percent of the country's total productive forest area Located on the southem most extremity of Bangladesh, the Sundarbans comprise an extensive flat, coastal and deltaic land formed by the confluence of the three mighty rivers of the Ganges, Brahmaputra and Meghna It is crl§-crossed by large tidal rivers as well as channels and creeks, all discharging into the Bay of Bengal.

The forest encompasses a land area of 6017 sq km, of which 1874 sq km constitute the river water area. The forest is bordered to the south by the Bay of Bengal while polders and a 'cultural land border the forest to the north. The westem border fohgws the Raimangal- Harinbhanga rivers, which also fomrs the intemational boundary with India. To the east lies the Baleshwar river and Meghna estuary There are rivers and canals spread acrrm this forest like a net with their innumerable branches. Nearly 450 large and small rivers occupy about 1 lakh 75 thousands 685 hectares or about 50 per oent of the Sundarbans. The biggest river is the Pusur. Other rivers worth-mention are Baleswar Sibsa, Ar-pangasia, Bhola, Horlnbhanga, Kalindi, Andharmanik, Raimangal, Kapotaksha, Koira, Shela Bhadra etc As one prooeeds to the south, the rivers widen. Some rivers are so wide that one cannot see one bank forrn the other Baleswar and Pusur rivers and their tributaries and distributaries are connected with the Ganges. As a result these rivers and their branches have flow of sweet water The Sibsa and other rivers in the westem part have daeir source of sweet water only in the Ganges and the northern portion of the Sundarbans depend upon the rain water As a result, the sweet water flow in these rivers decreases during the dry season when there is a massive intrusion of saline water. Moreover the condition of the rivers and canals in the Sundarbans is deteriorating. Shoals are fomiing and navigability is declining. Rover erosion is taking place at some places.

Tire forest is within the three administrative districts of Khulna, Satkhira and Bagerhat. Administered by the Forest Department (FD), the area is divided into four forest ranges, namely; Sarankhola, Chandpai, Khulna and Burigoalini. Three patches of the forest in the

south have been declared as "Mldlife Sanctuaries". They are Kachikhali-Katka sactuary in the Sarankhola range, Neelkamol at Hiron point in Khulna range and Mandarbari in the Burigoalini range. They have been declared by UNESCO in 1997 as the "World Heritage sires". The forest is flat and the maximum ground elevation is 3 meter above the mean sea level. The land developed through the process of sedimentation, subsidence and down-wrapping of sediments. The soil is deep alluvium of silty clay loam. lt has a tropical humid climam with temperature ranging between 20.4 degree and 51.5 degree Centigrade. The annual rainfall is between 1640 and 2000 mm. The rainfall is strongly seasonal and 85 percent falls during the monsoon, july-October Semi-diumal type tidal inundation regulates the hydrology of the forest. The four main seasons are pre-monsoon

(March-May), monsoon Uune-September), post-monsoon (October- November) and dry winter (December-February). The pre-monsoon period is characterized by the southerly winds, high temperature and high rate of evapo-transpiration with occasional heavy thunderstom1s and norwesters. The forest areas are inundated by tidal water increase which also raises the salinity of river water, The monsoon ushers in high rainfall, humidity and cloud cover Sediment load and water levels of the rivers also increase. The salinity level is lowered due to the influence of onrushing fresh water from the upstream region. Occasional thunderstorms, cyclones, stomr surges and rising salinity levels of river water occur during post-monsoon season, Generally, violent cyclonic storms brew in the Bay from mid- May to midjune due to north coastal winds, Cyclones also occur in October and early November The dry winter season is characterized by cool, dry and surmy weather with low precipitation. There is a ular belief that the "Sundarbans" derived its name from the Sundangofq-lerltiera fomes) trees, a maior oomponent of the forest.  Pageé Slate ol' Sundarbans legends also have it that the forest received its name from foreign explorers, who termed it as "the jungle of sundry trees" or diverse kind of trees, which finally came to be called the "Sundrybans". There is mother popular folk tale that the very name originated from local word "Samundar" meaning the seas, which later was changed to "Sarnundarbans". Floral diversity The forest supports a diversified flora and fauna. The floristic composition of the Sundarbans encompasses a variety of plants including trees, shrubs, grasses, epiphytes and lianas. Being mostly evergreen, they possess very similar physiological and structural adaptations. As the tidal estuaries deposit vast amount of nutrientrlch silt ln the deltaic region, they provide an ideal condition in the Sundarbans for the propagation of thick vegetation. Seemingly natural and simple, the succession of mangroves is in reality quite complicated. Each and every species in the Sundarbans has to struggle to grew and survive. Salinity soil conditions, nutrients, weather hazard, sunshine, temperature, Cyclones, tides etc. render the existence of every species difficult in various stages of life cycle. The uniqueness of the Sundarbans reserve forest lies in its diversity of species. Itis interesting to note that tree height is relatively shorter in the west-southem pans and longer in east-northem parts of the forest. Another fascinating feature of the forest is that water of the former region is more saline than that of the latter region. Flora includes 66 species of plants of which 51 are trees, The others are shrubs and climbers. The distribution of the species is not uniform and primarily controlled by the level of salinity and not by the tidal inundation which is fairly uniform, On the basis of salinity level, three zones are recognized : fresh water zone, moderately saline zone and highly saline none. Salinity increases from east to west and north to south. Altogether 15 forest and four non-forest types of vegetation have been identihed of which the Sundari (Heritiera fomes), Gewa (Excoecaria agallocha) and Garan (Ceriopls decandra) are dominant in the fresh wamr; moderately saline and ighly saline zones respectively The Sundari prefers fresh water flushing, drainage predominance and lirm higher ground. It is vulnerable to fungal infection and top-dying of the trees makes their survival difficult. Commerclaily it is the most sought after tree, comprising about 21% of the forest cover of Bangladesh part of the Sundarbans. Gewa can tolerate high salinity and grows in groves in association with the Sundari, Bain, Hental and Goran bushes. Commercially very important, the Gewa timber is used for paper pulp and in match factories. Garan species of the mangroves

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grow in the southem Sundarbans, where the tidal influence is high. Being the fuelwood most in demand in the Sundarbans, Garan is also used as a building material. The other major trees are Keora (Sonneratia apetala), Ora (Scaseolaris), Passur (Xylocarpus mekongensis), Dhundul (Xgranatum), Bain (Avicennia alba), Kankra (Bruguiera gymmotrhiza). Keora and Ora look similar in appearance but Keora being bigger; spreads its branches much more extensively The Keora is the most graceful and tallest tree in the Sundarbans. Ecologlcally Keom is the most imponant tree in the mangrove food chain. Birds, bats, rats, mortkeys, deer; fishes, insects get their food from its bark, leavm and fruits. Passur is the most praised timber in the Sundarbans as it is used both as building material and fumiture timber:Hental (Phoenix paludosa) is another member of the palm family commonly found throughout the Sundarbans. It is usually a slender straight, small tree which can attain a height of6 meter, The stems of the hentai are harvested throughout the year and is sold for making rafters, fence and house-posts. The Golpatta (Nypa fruiticans) grows abundantly along the banks of the Sundarbans rivers a.nd creeks. It is a stemlm palm whose leaves look like ooconut fronds and are mainly used for thatching roofs. Bala (Hibiscus tiliaoeous) is a scrambling woody shrub found along the river banks and is extensively harvested for fuelwood. Garian andjhanna possess stilt roots, their leaves are thick and wide, They usually grow along the soggy banks of the creeks. Hogla or Elephant Grass (Typha elphantina) ls a pioneer species generally found on riverbanks, estuarine chars (shoals) and along the edge of streams. It is used for making mats and as thatching mawrlal for temporary sheds. Faunal variety Animals have to struggle for life in the Sundarbans due to the forests adverse and hostile environment. Almost all the species can tolerate brackish water and subsist on their water intake from food, All the resident species of aquatic ma.mmals, reptiles and amphibians are powerful swimmers and habituated to meeting food re ulrements partially from aquatic sources, All the terrestrial animaéls such as birds, reptiles, fishes, plankton etc, are well adapted to the daily periodical and seasonal tidal rhythms. All animals including birds restrict their movement during the high tide. But fshes find the high tide ideal for feeding. Sundarbans faunas include 52 species of mammals, 226 species of birds, 35 species reptiles and 8 species of amphibians.