MANGROVE SWAMPS CASE STUDY; THE SUNDARBANS OF BANGLADESH
The Quality and Status of the Existing Mangrove;
PHYSICAL FEATURES The Sundarbans, covering some 10,000sq.km of land and water, is part of the world's largest delta (80,000sq.km) formed from sediments deposited by three great rivers, the Ganges, Brahmaputra and Meghna, which converge on the Bengal Basin (Seidensticker and Hai, 1983). The total area of the Bangladesh Sundarbans is 5,771sq.km (almost 62 percent of the total), of which 4,071sq.km is land and the rest water (Christensen, 1984). This area is approximately half the size of the area of mangrove that existed 200 years ago, the other half being cleared and converted to agricultural land (Hussain and Archarya 1994).
The land is moulded by tidal action, resulting in a distinctive physiography. An intricate network of interconnecting waterways, of which the larger channels of often a mile or more in width run in a generally north-south direction, intersects the whole area. Innumerable small khals drain the land at each ebb. Rivers tend to be long and straight, a consequence of the strong tidal forces and the clay and silt deposits which resist erosion. Easily eroded sands collect at the river mouths and form banks and chars, which are blown into dunes above the high-water mark by the strong south-west monsoon. Finer silts are washed out into the Bay of Bengal but, where they are protected from wave action, mud flats form in the lee of the dunes. These become overlain with sand from the dunes, and develop into grassy middens. This process of island building continues for as long as the area on the windward side is exposed to wave action. With the formation of the next island further out, silt begins to accumulate along the shore of the island and sand is blown or washed away (Seidensticker and Hai, 1983). 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 (Seidensticker and Hai, 1983).
Alluvial deposits are geologically very recent and deep. The soil is a silty 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. In the eastern part of the Sundarbans the surface soil is soft and fertile, whereas it is harder and less suitable for tree growth in the west (Choudhury, 1968). The pH averages 8.0 (Christensen, 1984).
CLIMATE Rainfall is heavy and humidity high (80%) due to the proximity of the Bay of Bengal. About 80% of the rain fall in the monsoon, which lasts from June to October. Mean annual rainfall varies from about 1,800mm at Khulna, north of the Sundarbans, to 2,790mm on the coast. There is a six-month dry season during which evapotranspiration exceeds precipitation. Conditions are most saline in February-April, the depletion of soil moisture being coupled with reduced freshwater flow from upstream. Temperatures rise from daily minima of 2-4°C in winter to a maximum of about 43°C in March and may exceed 32°C in the monsoon. Storms are common in May and October-November and may develop into cyclones, usually accompanied by tidal waves of up to 7.5m high (Seidensticker and Hai, 1983). Climatic data for Khulna are summarised by Christensen (1984).
VEGETATION The mangroves of the Sundarbans are unique when compared to non-deltaic coastal mangrove forest. Unlike the latter, the Rhizophoraceae are of only minor importance and the dominant species are sundri Heritiera fomes, from which the Sundarbans takes its name, and gewa Excoecaria agallocha. The reason for this difference is the large freshwater influence in the north-eastern part and the elevated level of the ground surface. The Sundarbans can be classified as moist tropical seral forest, comprising a mosaic of beach forest and tidal forest (Champion, 1936). Of the latter, there are four types: low mangrove forests, tree mangrove forests, salt-water Heritiera forests and freshwater Heritiera forests. Sundarbans West occurs within the salt-water zone, which supports sparse Ecoecaria agallocha, a dense understory of Ceriops, and dense patches of hantal palm Phoenix paludosa on drier soils. Dhundal and passur Xylocarpus spp., and Bruguiera occur sporadically throughout the area. Sundri and gewa cover most of the Sundarbans but Oryza coarctata, Nypa fruticans and Imperata cylindrica are prevalent on mud flats (Khan, 1986). Large stands of keora Sonneratia apetala are found on newly accreted mudbanks and provide important wildlife habitat (R.E. Salter, pers. comm., 1987).
Prain (1903) gives an account of the flora of the mangrove forest of the Ganges- Brahmaputra delta. Seidensticker and Hai (1983) report a total of 334 plant species, representing 245 genera, present in the Bangladesh portion of the delta, and list principal woody and herbaceous species. Chaffey and Sandom (1985) provide a detailed list of trees and shrubs in the Bangladesh portion. Islam (1973) provides an account of the algal flora of the mangroves.
FAUNA The Sundarbans 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, namely Javan rhinoceros Rhinoceros sondaicus (CR), water buffalo Bubalus bubalis (EN), swamp deer Cervus duvauceli (VU), gaur Bos frontalis (VU) and probably hog deer Axis porcinus (LR) have become locally extirpated since the beginning of this century (Salter, 1984). The only primate is rhesus macaque Macaca mulatta, considered by Blower (1985) to number in the region of 40,000 to 68,200, based on surveys by Hendrichs (1975) and Khan (1986), respectively, as compared to the much higher estimate of 126,220 derived by Gittins (1981).
The Sundarbans of Bangladesh and India support one of the largest populations of tiger Panthera tigris (EN), with an estimated 350 in that of the former (Hendrichs, 1975). Again, Gittins' estimate of 430-450 tigers may be overoptimistic (see Blower, 1985). Spotted deer Cervus axis, estimates of which vary between 52,600 (Khan, 1986) and 80,000 (Hendrichs, 1975), and wild boar Sus scrofa, estimated at 20,000 (Hendrichs, 1975), are the principal prey of the tiger, which also has a notorious reputation for man-eating. Of the three species of otter, smooth-coated otter Lutra perspicillata (VU), estimated to number 20,000 (Hendrichs, 1975), is domesticated by fishermen and used to drive fish into their nets (Seidensticker and Hai, 1983). Other mammals include three species of wild cat, Felis bengalensis, F. chaus and F. viverrina, and Ganges River dolphin Platanista gangetica (EN), which occurs in some of the larger waterways. Species accounts and a check-list are given by Salter (1984).
The varied and colourful bird-life to be seen along its waterways is one of the Sundarbans' greatest attractions. A total 315 species have been recorded (Hussain and Acharya, 1994), including about 95 species of waterfowl (Scott, 1989) and 38 species of raptors (Sarker, 1985b). Among the many which may be readily seen by the visitor are no less than nine species of kingfisher, including brown-winged and stork-billed kingfishers, Pelargopsis amauropterus (NT) and P. capensis, respectively; the magnificent white-bellied sea-eagle Haliaeetus leucogaster which, at a density of one individual per 53.1km of waterways (Sarker, 1985), is quite common; also the much rarer grey-headed fish eagle Ichthyophaga ichthyaetus (NT), Pallas's fish-eagle Haliaeetus leucoryphus and several other raptors. Herons, egrets, storks, sandpipers, whimbrel, curlew and numerous other waders are to be seen along the muddy banks and on the chars or sandbanks which become exposed during the dry season. There are many species of gulls and terns, especially along the coast and the larger waterways. Apart from those species particularly associated with the sea and wetlands, there is also a considerable variety of forest birds such as woodpeckers, barbets, shrikes, drongos, mynahs, minivets, babblers and many others (Salter, 1984). Scott (1989) gives further details of the avifauna.
Some 53 reptile species and eight of amphibians have been recorded (Hussain and Acharya, 1994). Of these mugger Crocodylus palustris (VU) is now extinct, probably as a result of past over-exploitation, although it still occurs in at least one location nearby (R.E. Salter, pers. comm., 1987). Estuarine crocodile C porosus still survives but its numbers have been greatly depleted through hunting and trapping for skins. There are also three species of monitor, Varanus bengalensis, V. flavescens and V. salvator, and Indian python Python molurus (NT). Four species of marine turtle have been recorded from the area, olive ridley Lepidochelys olivacea (EN) being the most abundant. Green turtle Chelonia mydas (EN) is rare due to excessive fishing, while loggerhead Caretta caretta (EN) and hawksbill Eretmochelys imbricata (CR) are not common although there have been some reported on the beaches (Hussain and Acharya, 1994). River terrapin Batagur baska (EN) is also present. The eighteen recorded snake species include king cobra Ophiophagus hannah and spectacled cobra Naja naja, three vipers and six sea-snakes (Salter, 1984).
Over 120 species of fish are reported to be commonly caught by commercial fishermen in the Sundarbans (Seidensticker and Hai, 1983). According to Mukherjee (1975) only brackish water species and marine forms are found in the Indian Sundarbans, freshwater species being totally absent. This may be assumed to apply also to the Bangladesh Sundarbans, except possibly in the eastern portion where there is freshwater in Baleswar River. Mention should also be made of mud-skippers or gobys which occur in large numbers and are a characteristic feature of mangrove swamps.
Crustacea account for by far the largest proportion of animal biomass, with an estimated 40 million kilograms of fiddler crabs and 100 million kilograms of mud crabs (Hendrichs, 1975). The nutrient-rich waters of the Sundarbans also yield a considerable harvest of shrimps, prawns and lobsters. The area supports a varied insect population including large numbers of honey- bees, honey and beeswax being among the economically important products. The insect life of the Sundarbans has been little studied.
Describe the degradation threat to the Sundarbans mangrove;
The Sundarbans are under threat from;
· Encroachment from human settlements and agriculture.
· Deforestation of the mangrove in the vicinity of settlements related to the growing populations need for;
Þ FoodÞ FuelÞ Shelter
· Construction of barrages for irrigation dependent agriculture.
· Main factors contributing to degradation and depletion;
Þ Economic growth Þ Accessibility and unclear ownership of mangrove land.
Þ Obscure management plans and rules/regulations by bureaucracy.
Þ Inadequate logistic support
Þ Lack of awareness.
· Construction of coastal embankments has changed sediment pattern, and contributed to the vertical growth of deltaic landforms. This has transformed a hydrologically synchronised biota in to a marginalized and scattered ecosystem.
The Sundarbans Reserve Forests composed of 0.58 million ha of area (greater Khulna and Bagerhat region) of which 0.41 million ha is mangrove forests and 0.17 million ha is open water areas in rivers, channels and creaks. The Sundarbans is the largest single tract mangrove formation in the world. The main species is Sundri (Heritiera spp) and other associated mangroves mainly species belongs to Rhizophorace family (Sonneratia spp., Excoecaria spp., Xylocarpus spp., Ceriops spp. etc.). The forest is fully controlled and managed by the Government Forest Department. This is legally declared as a Reserve Forest so there is no human habitation and locality inside the forest except some in the periphery. The Sundarbans constitute about 45 percent of the natural productive forests and provide livelihood for at least 0.5 million people mainly wood cutters, fisherman, honey collectors and Nypa palm leaf (fronds) locally known as Golpata collectors, Phoenix paludosa (hental) collectors, shell collectors and fishermen. Beside forest resources, the Sundarbans forest is extremely important for fish production, wildlife conservation, recreation and serves as a protective barrier against coastal erosion, cyclones, storms and tidal surges. The mangrove forests and mudflats of the Sundarbans provide the vital breeding and nursery grounds for a large proportion of the fin fish, crustaceans and molluscs. The significant depletion of the growing stock, notably of Heritiera (Sundri) and Excoecaria (Gewa) appears to have been reduced by 40% and 45% respectively between 1959 and 1983. The incidence of top dying of Heritiera spp which seems to be increasing with rapid ecological changes rendering the site unsuitable for the species. The lack of experienced and trained staff, inadequate data base, accessibility are also the main problems to manage the forest properly.
The main reasons of the depletion of this forest are due to the corruption and negligence of the some Forest Department staffs, illegal traders, local influential leaders, some government officials concerned, and sections of the media and police forces. Often the local poor people are used to destroy the forests taking tolls (many times higher than government rate) from them illegally. Other reasons are improper and poor management, over exploitation and also ecological reasons to some extent. The construction of the Farraka barrage over the upstream of the Ganges by India in West Bengal, reduced the water flow significantly during dry season which increased the salt intrusion from the sea water and altered/modified the ecosystem. The causes of the 40% top-dying of the main species Sundri (Heretiera spp) is still only partially known.
Describe and explain the management policies of (i) wood resources, and (ii) non-wood resources;
The Government of Bangladesh formulated the National Forestry Policy on July 8th, 1979. Since then initiatives have been taken to re-orient the policies with current need, particularly as they relate to the depletion of forestry resources owing to numerous socio-economic factors. A recent draft of the Policy (1994) identified some key factors;
· Forests should be carefully preserved and scientifically managed. Attempts will be made to afforest up to 20% of the country, and private initiatives will be used to complement this.
· Attempts will be made to increase the amount of protected land by 10% by 2015.
· Inaccessible areas will be identified and kept as protected forests. Modern technology shall be employed for extraction and use of forest produce.
· Emphasis will be taken on forest based industries to ensure effective utilisation of the forest raw materials and profit orientated management systems under the free market economy.
· Rules and procedures regarding forest produce will be simplified and modernised. Reserved forest cannot be used for non forest purposes without the express permission of the Head of Government.
· Timber resources are to be increased by establishing large scale plantations.
· Ecotourism related to forest and wildlife is recognised as forestry related activity, which will be promoted taking into consideration the caring capacity of nature.
· The forest department will be strengthened to achieve the goals, and research, education and training will be organised to meet the scientific, technological and administrative needs of the country.
· Laws, rules, and regulation related to the forestry sector will be amended and updated as necessary in consonance with the objectives of the National Policy.
· Rotation of the cutting forest takes place every 20 years. the principal practice being that all trees above a certain diameter at a certain height are removed, provided that their removal does not leave a permanent hole on the canopy.
There are a lot of controversial estimates among the organisations on the scale of forest area and the deforestation rate in the country. In Bangladesh, though forest land is 18-19% of the total land area, 10-12% are declared as forest and tree cover is only 5-7% according to a present estimate. Other estimate says that the total natural forest cover 769000 ha which is 5.9% of total land area and the area of plantations is 335000 ha which is 2.5% of the total land area (FAO, 1993).
The Ganges, the Jamuna and the Meghna river system with their tributaries, one of the largest in the world (watershed area is about 1090000 sq. km) brings 2.4 billion tonnes of silt per year and the coastal land of Bangladesh is growing towards the Bay of Bengal. The rate of new accretion was 35 sq. km/year in 1989. These lands are more or less stable and suitable for artificial mangrove afforestation. Realising the above facts the government Forest Department (FD) started a massive afforestation programme since 1965 and up to June, 1985 an amount of 37000 ha coastal land had been planted. The total area of present coastal plantation may be about 89000 ha. The FD estimated area is probably more but contradicts with the survey of Space Research and Remote Sensing Organisation (SPARRSO) in Bangladesh. The available area for future plantation in the coastal region in Bangladesh may be about 100000 ha.
There are 57000 wood industry production units with 0.21 million employees. Primary industries include sawmilling and pulp and paper, plywood/veneer, match and panelboard. Secondary industries are furniture, seasoning, treatment and preservation. The estimated demand for saw logs in the country in 1991 was 4.3 million m3 compared to a sustainable local supply of 1.3 million m3 . The 1993 total wood supply is 6.2 million m3 against a demand of 8.34 million. Sixty-five percent of forest products are consumed as fuelwood. Unrecorded production, illicit felling and smuggling accounts for 20% of supplies (GOB, 1993). Including all aspects, estimated total forestry employment today is 0.8 million persons. However, considering its seasonal nature, possibly up to 1.5 million people benefit from forestry related work directly. Forestry sector contributes to about 3% of total GDP in Bangladesh. There are intangible benefits, which are not considered in financial terms.
Non wood resource management;
Management of the mangroves is based on plans and the silvicultural systems. The integrated management of wood and non-wood resources depends upon an understanding of the ecological and silvicultural parameters of forest management, and the biological role that primary production from the forest plays in the mangrove food web of aquatic resources. An understanding of the key species which maintain the equilibrium of the ecosystem is similarly essential.
Sustained yield management of the mangroves for commercial fisheries involves the retention of the mangroves to provide nutrients. This will increase the value of the fisheries for nursery, breeding and permanent habitats. The multiple use system is known as Silvofishery. Constructing fish or shrimp ponds around mangrove plantations has been very successful in Indonesia.
Both management plans are couched in terms of conservation but are underlain by a hard business theme. For example, the unprofitable areas (inaccessible) are those which are preserved and kept as National Forest. The easy to cultivate slopes are utilised to their maximum potential, using modern technology. A government driven system, similar to the Russian state culture determines the market production figures.
In addition to their own role, the Bangladeshi government must also take on the responsibility of providing for the World Heritage Site, which was designated in 1997. They are responsible as a state to preserve the forests and mangroves of the Sundarban, but also to create a dynamic economic community within them, and to utilise fully the resources which they provide in a self sustaining manner. However, the evidence shows that the world importnce of the Sundarbans has taken over in the country, and increasingly, supranational organisations are making the decisions and planning for the preservation and management of the area.
The Sundarbans is the only sizeable mangrove forest in the world managed for commercial timber production and it has been under some sort of management since 1879. Early management consisted on revenue collection by enforcing simple felling rules. Subsequently, the progressive enforcement of felling rules reduced the amount of over-cutting of the four species for which felling rules were established. Bangladesh part of Sundarbans is managed as a continuous block of mangrove forest with no permanent human habitation inside.
The Sundarbans has been the subject of a series of successively more comprehensive working plans since its declaration as reserved forest, the most recent of which points out the importance of the tiger in controlling the spotted deer population, and also mentions the intention of establishing compartments 3-7 as a 'game sanctuary', a total area of some 52,320ha (Choudhury, 1968). A plan relating specifically to wildlife conservation was prepared under the joint sponsorship of the World Wildlife Fund and the National Zoological Park, Smithsonian Institution (Seidensticker and Hai, 1983). Emphasis is directed towards managing the tiger, together with all wildlife, as an integral part of forest management that assures the sustainable harvesting of forest products and maintains this coastal zone in a way that meets the needs of the local human population. The Sundarbans Forest Development Planning Mission, carried out by FAO in conjunction with the Bangladesh Forest Department in February-May 1984, collected all available data related to the use and management of forest products, wildlife and fisheries, assessed development potential and prepared proposals for further integrated development and conservation of the natural resources of the area (Christensen, 1984; Salter, 1984). More recently, Blower (1985) reviewed wildlife conservation in the Sundarbans Reserved Forest as part of the Sundarbans Forest Inventory Project, carried out by the Bangladesh Forest Department and the Land Resources Development Centre of the UK Overseas Development Administration. The main purpose of the project is to provide the necessary data on which to base future exploitation of the forest for sustainable use of timber, fuelwood and other forest produce, with due consideration to wildlife conservation and the social amenity value of the area. It has been recommended that the Sundarbans be managed as a single unit with full protection afforded to both wildlife and habitat in the wildlife sanctuaries, and with forest resources exploited at sustainable levels but wildlife protected elsewhere in the reserved forest. The establishment of intermediate buffer zones, in which disturbance is kept to a minimum through restriction of access, is recommended in areas peripheral to sanctuary boundaries. A new management plan is due to be prepared, based on data collected in 1995, and is expected to include detailed prescriptions concerning the conservation and management of the sanctuaries.
A long-term ecological change is taking place in the Sundarbans, due to the eastward migration of the Ganges, abandonment of some distributaries, diversion of water and withdrawals for irrigation. (Up to 40% of the dry season flow of the Ganges has been diverted upstream, following the completion of the Farraka Barrage in India in 1974.) Decreased freshwater flushing of the Sundarbans results in increased saline intrusion, particularly in the dry season. Concern has been expressed about recent indications of apparent deterioration in the flora, including localised die-back of sundri, commercially the most valuable of tree species. Top-dying of sundri is most likely associated with the decrease in freshwater flow, either as a direct effect of increasing salinity or other associated edaphic changes. A gradual replacement of Heritiera with Excoecaria, therefore, is a likely long-term effect (Christensen, 1984). While deterioration in the vegetation is already well-documented (International Engineering Company, 1977 and 1980) and is the subject of continuing study, no attention has yet been given to the possible effects which these changes might have on the fauna. It is perhaps significant, however, that the stocking of spotted deer appears lower in western areas, where salinity is highest, than in the east where it is lowest. Oil spills are another potential threat and could cause immense damage, especially to aquatic fauna and seabirds and probably also to the forest itself (Blower, 1985). There have been several spillages from tanks passing nearby. The most recent incidence due to ship wreckage occurred in August 1994 when a Panamanian cargo ship capsized near Dangmari Forest Station. Oil from the fuel tank spread about 15km downstream from the ship and affected a considerable part of the Sundarbans mangrove area. It was found to cause instant mortality of seedlings of Heritiera and Excoecaria while patches of grass which were covered by oil also died. Mortality of fishes, shrimps and other aquatic animals from the Sundarbans has been reported to due the incidence (Hussain and Acharya, 1994).
Cyclones and tidal waves cause some damage to the forest along the sea-face, and are reported to result occasionally in considerable mortality among spotted deer. The most immediate threat is over-exploitation, both of timber resources, which may have already taken place, and also of the fauna. Agricultural encroachment has already occurred to a limited extent on the eastern and western boundaries and, with increasing population pressure in surrounding settled areas, could reach serious proportions unless checked. Fishermen's camps are a major source of disturbance. There is extensive illegal hunting and trapping, not only by fishermen and woodcutters but also reportedly by naval and military personnel from Hiron Point in Sundarbans South Wildlife Sanctuary (Blower, 1985).