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Vol. 8 No. 4 - Oct 2002

Biodiversity and Floristic Composition of Sundarbans in Bangladesh

By: M. N. Amin

The popularly known Sundarbans, mangrove (tidal/littoral forest) forest of Bangladesh, is undoubtedly the largest mangrove system in the world. The World Heritage Committee of UNESCO in its convention concerning the protection of the world cultural and natural heritage in Naples, Italy in 1997 inscribed the Sundarbans as the world heritage site in Bangladesh. The forest is unique for supporting an exceptional biodiversity with a wide range of flora and fauna and concurrent functioning of the significant ecological processes; monsoon rains, flooding, delta formation, tidal influence, and plant colonization and climax formation.

Sundarbans is bounded in north by Bagerhat, Khulna and Satkhira districts, in the south by Bay of Bengal; in the east by Baleswar (or Haringhata) river, Perojpur and Barisal districts; and in the west by Raimanghal and Hariabhanga rivers, which partially form the boundary of Bangladesh with West Bengal in India. At its maximum extent the forest is about 70 miles wide from north to south and about 180 miles long from east to west.

The socio-economic importance of Sundarbans is enormous. It supports many industries as well as local economy and communities by supplying raw materials, and employing people for their subsistence and livelihood. The forest is acting as shelterbelts against natural calamities like storms, cyclones and tidal bores thus protecting the establishments and properties of the people inhabiting in coastal areas from such activities. The environmental importance of the forest is also worth mentioning. Some of the important socio-economic services of the Sundarbans are described briefly in the following paragraphs:

It is often said that most part of Bangladesh was originally well vegetated, with coastal mangroves backed up by swamp forests and a broad plain of tropical moist deciduous forest. However, more than 90% of the original vegetation has been cleared during the last 50 years or so. Now the ecosystem is changing rapidly and biodiversity is depleting fast with the extinction of some species of the forest. This changing scenario of Sundarbans creates real concern to the responsible society.

The Sundarbans of Bangladesh that extends westwards into India is the largest mangrove system of the world, followed by the mangroves of Irian Jaya of Indonesia. An intricate network of interconnecting waterways, of which the large channels in a generally north-south direction, intersects the whole area. The Sundarbans provides ideal habitats for a variety of unique plants and animals. The forest is rich in biodiversity with about, 334 species of plants, 270 species of birds, 42 species of mammals and 210 species of fishes, including 32 species of prawns. It is also famous for the natural habitat of a variety of wild animals, the important among them are tigers, deers, wild boars, wild fowls, monkeys, otters, crocodiles, birds, pythons, lizards, amphibians, molluscs, crabs and different varieties of snakes.

Alongside the recorded 42 species of mammals, waders and seabirds find the Sundarbans as their suitable habitats and also both marine turtles and the endangered estuarine terrapin, Batagur baska find it as their suitable nesting site. But above all, the Sundarbans is well known as the home of the famous Royal Bengal Tiger, Panthera tigris, whose population is estimated at 350 to 600, one of the largest surviving populations in the world.

The floristic composition of Sundarbans, was first described by Prain (1903) with 334 species and 245 genera in 75 families of plants including small to large trees, shrubs, climbers, grasses and herbs. So far, no similar study and detailed inventory have been made on the vegetation, although ODA (1985) has listed 130 species of commonly found higher plants and Islam (1976) has reported 165 species of algal flora from in and around the mangrove ecosystem. However, among various types of plants some are endemic to the Sundarbans. The forest is rich in epiphytic ferns, parasitic plants and orchids; among the 66 species of orchids found in the forest about 13 are epiphytic.

The vegetation of Sundarbans is unique in many respects such as floristic diversity, composition, association and abundance. It is also interesting to note that tree height is relatively shorter in South-Western parts and longer in North-Eastern parts of the forest.

The forest has a glorious past with a written history of more that one thousand years. It acts as a natural safeguard to protect the entire coastal region at the north of Sundarbans from cyclones and tidal bores. The environmental importance of the forest as green shelterbelt can be assumed from the devastation and death toll caused by such catastrophic events in the coastal areas where there is no mangrove forest like Sundarbans. However, during the 1950s Sundarbans by and large was not inhabited at all and most forest areas were virtually inaccessible. However, mass destruction of the forest environment by human efforts began during the early 1960s. According to one estimate the Sundarbans had a total area of about 67O thousand hectares just a decade ago. Unfortunately, we have lost more than one-third of its area during the recent past that has reduced the forest area to about 420 thousand hectares. A major recent change in the physical environment of the Sundarbans is a reduction in the amount of fresh water flowing into the area that resulted in considerable increase in salinity level. This is due to natural changes, river diversions, and construction of dams and withdrawal of freshwater for irrigation. It is believed to be one of the major causes of unusual mortality of the main commercial species "sundari", in some areas especially since 1970. It seems unlikely that the trend of decreasing freshwater discharge can be reversed; indeed the problem is likely to be aggravated by a rise in sea level caused by global warming. However, there have been considerable studies on environment and conservation aspects of the Sundarbans. Nevertheless, there seems to be a wide gap in implementing the recommendations of these studies as debates are going on in the issues of continued environmental degradation and unscrupulous harvesting of resources of the forest. There is, therefore, suggestions that eternal social vigilance and resisting reckless exploitation of forest resources, unplanned conversion of forestland for other uses and proper implementation of the conservation policies thus far formulated can only save our world heritage site. Under the threshold of unprecedented environmental degradation and imprudent resource harvesting the Sundarbans still provides every day earnings of millions of people, by working directly or indirectly on the natural resources of the forest.

THREATS TO BIODIVERSITY AND ECOSYSTEM

Plundering and unscrupulous exploitation of the forest resources by the state as well as production-oriented forestry system are said to be the main causes of forest loss in Bangladesh and consequently threat to the biodiversity. Recurrent natural calamities like cyclones and tornadoes are also big threats to the forest. About one and half dozen of cyclones have hit against Sunderbans only during the current decade. Alongside multifarious destructive anthropogenic activities and natural calamities some ecological changes like increase in salinity and sea level, and outbreak of diseases like top dying of trees occur in the recent time that pose serious threats to the rich biodiversity of Sundarbans.

Diversion of the natural courses of rivers through training activities, and construction of embankments, dams and bridges in the upstream as well as decreased flow of fresh water in the rivers resulted in the increase in salinity level and over silting in many places and subsequent changes in the mangrove ecosystem. Increased salinity and over silting within the forest may hinder the biological functions of the pneumatophores (breathing roots) and are supposed to be the major causes of top dying of the trees. Possibility of infestation by the fungal pathogens cannot be over looked. Dieback is also common in mesophytic plants like Guava and Sisso after a short period of rain/ flood water stagnation, which is caused by the Fusarium spp. that produce complex and fatal symptoms in the affected plants, popularly called as "fusarium-syndrome". The following reasons have been identified as major threats to the biodiversity of Sundarbans:

  • Population pressure, expansion of agricultural land, constructions of houses, roads, etc., and grazing by domestic animals.
  • Unscrupulous harvesting of forest resources and insufficient measures to regenerate the resources.
  • Indiscriminate use of chemical fertilizers and insecticides in croplands and adoption of unplanned agricultural practices.
  • Lack of appropriate policies for proper management and expansion of wild life sanctuaries /protected areas.
  • Lack of proper education, training and research for implementing conservation strategy so far recommended.

CONSERVATION NEEDS

Maintaining the biological integrity of the forest ecosystems, whose importance we often appreciate but do not as yet understand, presents difficulties to researchers developing a sustainable management system especially under current levels of natural and man made threats to the forests.. It is obvious that in recognition of the rich biodiversity of the Sundarbans it has been declared as a World Heritage Site in Bangladesh. The country is thus pledge bound to protect the treasure of natural resources [both the biotic and abiotic] of the forest.

It is estimated that a number of species among plants, fishes, reptiles, birds and mammals are threatened with extinction for various reasons. Therefore, taking appropriate measures for conservation of biodiversity in Sunderbans should be the highest priority. However, to protect and conserve the rich biodiversity of Sundarbans three wildlife sanctuaries (protected areas) have been established, these are considered to be not sufficient to represent the delicate ecosystem of the mangrove forest. There is an urgent need for a holistic and integrated approach of biodiversity conservation involving in situ and ex situ strategies along with community participation and use of indigenous knowledge en route to biocultural restoration of the mangrove ecosystem.

In all considerations the ecosystem of Sundarbans demands urgent and sustainable management. Nevertheless, some interested groups are embarking on oil and gas exploration in the Sundarbans. It is said that any exploration in the forest area must be forbidden. If we fail to forbid such exploration that may lead us to a catastrophic environmental condition where the very existence of the "Lush Green Bangladesh" would surely be in jeopardy.

Dr. Muhammad Nurul Amin is-Professor in Department of Botany at-University of Rajshahi, Rajshahi-6205,-Bangladesh.


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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