-Les mangroves, une richesse trop longtemps ignorée

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role mangrove forêts cotières

We have tended in the past to regard mangrove swamps as being of little use to humans. They occupy muddy coastlines in tropical regions, tend to be infested with mosquitoes, and are easily flooded by the sea or inland waters. But the mangrove swamp is a transitional ecosystem, as productive as it is biologically rich. It is composed of one or several species of mangrove, a tree that has aerial stilt-like roots which support the main trunk like flying buttresses, and is home to a large number of fish, mollusks, and crustaceans, which begin life in these mangrove nurseries before rejoining the open sea. By trapping the sediments carried by the rivers and the tides, mangrove swamps also protect tropical coastlines from erosion and the assaults of storms, cyclones, and tsunamis, while ensuring that the waters remain clean enough to sustain their coral reefs.

Humid zones and mangrove swamps are the two environ?ments that suffered the worst damage during the course of the 20th century. Between 1980 and 2005, according to the FAO, 20% of mangrove swamps were destroyed, and they now occupy a surface area of no more than 37.6 million acres (15.2 million hectares). Traditionally exploited for wood, these forests have been subjected more recently to vast clearance schemes linked to the development of shrimp farming in Southeast Asia and Latin America. Extension of agricultural land, harbor installations and seaside developments, and the general urbanization of coastlines are also causes of decline.

Experts have succeeded in establishing figures relating to the economic and social value of mangrove swamps. A hectare of mangrove swamp in the Gulf of California, for example, would generate some 37,500 US dollars a year, principally in the form of fish and crabs, commercial species whose life cycle is linked to the presence of the mangroves. Mangrove swamps would also help to limit the more dramatic effects of climate change and rising sea levels, while acting as effective carbon sinks.

Awareness of the environmental and also economic and social value of these forests has undoubtedly helped to slow the pace of destruction in a number of countries. In Bangladesh, the surface area of mangrove swamps is even increasing. But this is still the exception.

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