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close this bookUnited Nations University - Work in Progress Newsletter - Volume 12, Number 1, 1989 (UNU, 1989, 12 pages)
View the document(introductory text...)
View the documentSustaining the Earth
View the documentAnticipating global trends: Aspects of UNU work for the period 1990-1995
View the document'An uncontrolled global experiment...'
View the document'A little breathing space': Report from the Budapest
View the documentEnergy savings: Sooner much better than later
View the document'The rich get richer...'
View the documentOld wine in new bottles?
View the documentTectonics of the desert cities
View the documentMan in the mangroves
View the documentDiverting the Nile
View the documentLosing the soils of Africa
View the documentIn fairness to the future

Man in the mangroves

By J.R. Mainoya, S. Mesaki and F.F. Banyikwa

While relatively small in geographical area compared to other woodlands of the world, mangrove forests play an essential role in the ecosystems of many tropical coastline areas, the locale of some of the world's greatest population clusterings. Mangroves act as a wind and water break against erosion, and help maintain moisture and breeding grounds for plants and animals from both land and sea. To coastal villagers, they provide food, building materials, fibres, and medicinal plants.

The delicate ecosystems the mangroves help support are now under severe stress - due to rapid population growth, urban expansion and economic development. Moreover, mangrove poles, prized for construction in both the Arab and African world over the centuries, have their own important economic export value: they are thus just one more of those items to be tallied in the bewildering complex ledger the environmental economist now must maintain. The volume, Man in the Mangroves, is a report on a UNU workshop on the socio-economic situation of human settlements in mangrove forests, held at Nong Nuch Village, Pattaya, Thailand in 1985. The following excerpt is from a workshop paper on problems that have hit mangrove forest dwellers in the river estuaries and deltas along Tanzania's Indian Ocean coastline. Professor J.R. Mainoya is Dean of the Faculty of Science at the University of Dar es Salaam in Tanzania. S. Mesaki and F.F. Banyikwa are in the Department of Zoology and Marine Biology at the same institution. - Editor

Mangrove poles and bark have been exported from the eastern coast of Africa for a very long time. Trade between the Persian Gulf and East African ports dates back to a time when the Arabs secured a footing on the coast of East Africa. For centuries, dhows from the Gulf visited Lamu, Mombasa, Zanzibar, and the Rufiji delta during the north-east monsoon, bring with them dates, carpets, salt and earthenware - and taking back mangrove poles and firewood on their return journey during the south-west monsoon.

Studies of the Zanzibar Empire (1770-1873) have suggested that it was probably such commodities as grain, mangrove poles, and charcoal that initially attracted and sustained the attention of Arabs to East Africa. The importance of mangrove poles as a building material in Arabia during the beginning of this century has been well documented; as late as the 19th century the Sultan of Zanzibar retained a user right in the Rufiji delta, whence he derived free of charge a large number of poles and other building materials, even though the mangroves were then under German control.

Mangrove bark has also been exported for tannin extraction. In the 1930s, the potential export income from mangrove ecosystems was considered to be of sufficient importance for the then-government of Tanganyika to experiment with mangrove silviculture. Between 1923 and 1958, the mangrove pole trade was in the hands of private entrepreneurs, who employed local labour and overseers to exploit the mangroves of the Rufiji delta. In 1958 (following problems over royalties and local labour complaints), local co-operatives were formed to exploit the entire delta mangrove area.

This mangrove trade flourished up to 1960, when a decline set in, probably due to the economic changes that followed the discovery and large-scale exploitation of oil in the Arab Gulf countries. In 1976, co-operatives were banned by the government, and the mangrove trade was handed over to the para-governmental body, the Tanzania Timber Marketing Company which now handles all trade in mangrove poles with foreign countries. Despite the decline, the company in 1979 earned 4 million Tanzanian shillings in foreign exchange; about two-thirds of the poles exported were destined for Iran.

Local Uses

In addition to the export trade in poles, mangrove forest products are put to many uses locally. Poles are widely used in building and repairing ordinary Swahili homes in Dar es Salaam. Tannin extracted from mangrove bark is used by local lather-processing companies since the importation of tanning and dyeing agents has been restricted.

Mangrove wood is burned to produce excellent charcoal, but transportation difficulties have reduced the profitability and attractiveness of large-scale charcoal production. People in coastal villages use mangrove wood for firewood in their homes. Mangrove wood is also used as fuel in coast village industries in the production of burnt bricks and tiles and in lime burning.

The coastal people of Tanzania use mangrove products for many other purposes as well. These include boat hulls, masts and oars, fences for pig pens and fish traps. They use mangrove foliage as fodder for goats and cattle and a leaf extract is used as medicine for hernias.

Mangroves and Fisheries

Tanzanian mangrove waterways and areas submerged at high tide support important fish populations. Especially around the Rufiji delta, the mangroves serve two fishery-related roles: as a habitat and as a nursery ground for many species of shellfish and fin fish that can be exploited commercially. In addition, many women and children catch shrimp in these groves which is a factor in the rural economy. Estimates of the total prawn potential in Tanzania, based on a survey by a Japanese team in 1978, showed that up to 2,000 tons of prawns could be harvested each year.

Human activities are by far the most important factor influencing mangroves negatively in Tanzania today. One such activity is the clearing of land in and around mangrove forest to create salt evaporation pans. Tanzania produced 60,000 tons of salt from coast salt pans in 1981.

Although saltworks have been in production for several decades around Kunduchi, north of Dar es Salaam, significant reduction of the mangrove vegetation was not noticed until 1970. By the end of 1981, however, there had been a large expansion of the saltworks which reduced the once large Kunduchi Creek mangrove forest to a mere vestige. If this trend continues, the increasing demand for table salt in Tanzania is bound to produce a corresponding decline in mangrove habitats.

The Wider Impact

Conservation of the mangrove habitats and resources they contain is very important. The island of Mafia and the Rufiji delta mangrove forest have the potential to be a very rich marine park area. The delta supports dugongs and crocodiles, both of which are threatened species, and some islands around Mafia support the green turtle. In the Jozani forest on Zanzibar, the red colobus monkey has been observed to feed on the buds and young leaves of mangroves.

Tanzania has an excellent reputation for wildlife conservation on land. It would be very desirable if the government took a greater interest in mangrove forest conservation. It has been shown that unplanned cutting of mangrove forests often leads to coastal erosion and sediment mobilization - and this adversely affects marine life dependent on the nutrients associated with the mangrove ecosystem. The destruction of the mangroves may reduce not only coastal fishery resources, but also catches from off-shore fishing, far from the mangrove forest itself.

Mangroves protect tropical shores from erosion by tides and currents, and it has been recommended that a mangrove strip at least 100 metres wide should be left as a buffer zone on the more exposed shores. Also, if scientific forestry practices are to be applied in the mangrove areas, greater consideration should be given to those mangrove species that have been over-exploited for poles, firewood and charcoal. In addition, because regeneration of mangroves is a slow process, thinning of mangrove stands could be carried out where necessary to reduce tree density and promote growth of the remaining trees.

More and More People: Biggest Impact

The rapid growth of the human population in Tanzania is likely to increase the negative human impact on mangroves. The important role of mangroves in the preservation of coastal and offshore fish and shellfish stocks and the shore-protecting properties of mangrove vegetation make the preservation and sound management of mangrove-clad habitats an urgent matter for developing coastal states like Tanzania.

Mangrove communities in Tanzania have not been studied in sufficient detail to plan their rational exploitation. There is an urgent need for further studies of these ecosystems. Few integrated multi-disciplinary studies of mangrove forests have been made. Most studies have been of a reconnaissance nature, generally providing scanty information that cannot be used in land-use management plans.

Because the trade in mangrove plants is very lucrative, both for the internal market and for export, it is recommended that a plan for monitoring mangrove pole harvesting and utilization should be worked out. A strategy for growing the economically more important mangrove species could be investigated.

An Environmental Dow Jones?

Environmental economics might be described as the notion that the planet's biological and geophysical ups and downs are probably every bit as important to the state of the globe's economic health as are the latest trade reports - or stock market gyrations - from London, New York, Paris or Tokyo. The recognition of this has led the UNU's World Institute for Development Economics Research (WIDER) in Helsinki to an exploration of the ways in which economic systems have responded to environmental problems. (A specific example of the link between economic and environmental considerations is also discussed on this page in a selection, from the UNU volume, Man in the Mangroves, on the ecological implications of continued mangrove exports in Tanzania.)


In February of this year, 12 experts comprising both resource economists as well as general economists working in the area of resource allocation, met in Helsinki to discuss and refine the programme of work prepared by UNU/WIDER research advisers, Professors Partha Dasgupta of Cambridge University and Karl-Göran Mäler of Stockholm School of Economics.

The planning meeting considered specific research studies to be initiated within phase one of the project as well as the general outline of a textbook the project expects to produce. On the occasion of the gathering, a symposium was held on the topic, "The Environment and Emerging Issues in Economic Development." Professor Robert Solow, Institute Professor at MIT and the 1987 Nobel Laureate in Economics, and Professors Dasgupta and Mäler served as panel members. The symposium discussed both theoretical and policy-oriented issues raised by the emerging concern with the relationships between the environment and economic development.