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afrol.com, 11 September - Global warming, a rising sea level and human exploitation threaten the fragile mangrove habitat of Western Africa. Due to the loss of habitat, significant losses of endemic species are expected. "Many tropical species may be unable to move quickly anyway," professor Jay R Malcolm told afrol.com. Malcolm is an assistant professor at the University of Toronto (Canada), were he specializes in wildlife ecology, community ecology, tropical ecosystems, and landscape ecology. He is co-author of the WWF report Global Warming and Terrestrial Biodiversity Decline, released in August.
The mangroves are a characteristic forest biotope in tropical river estuaries and tidal zones. They constitute an incredible adaptation to the environmental conditions of entering salt, sea water and escaping sweet, riverine water. The forests are highly productive areas and are still widespread along the West African coast from Senegal to Congo. In August, afrol reported about a WWF study, which concludes that global warming could fundamentally alter one third of plant and animal habitats by the end of this century, and cause the eventual extinction of certain plant and animal species. Although having most effect in colder climates, several African habitats also are affected. The most threatened African habitats are the mangroves and mountainous areas. Guinea-Bissau is found on fourth place on the list over countries, ranked according to percent species loss as predicted due to the decrease in the area of persisting habitat patches. Some 2,9% losses were calculated. (2,9%). The effects of a rising sea level due to global warming are not included in that number. Guinea-Bissau, with its low altitude above sea level, mangrove coast and islands, stands the risk of loosing much of its territory due to the rising of sea level (see map). As global warming accelerates, plants and animals will come under increasing pressure to migrate to find suitable habitat. Some will just not be able to move fast enough," said Adam Markham, Executive Director of a US NGO, Clean Air-Cool Planet, one of the co-authors of the report. Professor Jay R Malcolm, however cannot guarantee for the accuracy of the high percentage calculated for Guinea-Bissau. "It is always better to interpret these scenarios at the regional level rather than for specific sites," he told afrol.com. "These models use coarse resolutions, and better capture regional patterns than local patterns." Guinea-Bissau comprises only very few pixels in these models. "This small sample size means that the mean percentages can be unduly influenced by just a few pixels." On a regional level, considering the mangroves of Western Africa, the calculations show significant results. From the Saloum delta in Senegal, through The Gambia, the Casamance, Guinea-Bissau and the coasts of Guinea, Sierra Leone and Liberia, the whole zone is characterized by its mangrove coast and broad belt of coastal lowlands. In particular Guinea-Bissau and the Gambia have high percentages of their territory affected. Some 20% of the Gambian territory is covered by mangroves.
"Not including sea-level rise, the fundamental question here, I would think, is whether or not mangroves can migrate fast enough to keep up with the new deposition," Malcolm assesses the situation. Secondly, of course there is the question it the mangroves would "be allowed to migrate inland, i.e. if land exists that is not developed or otherwise under human management." In Western Africa, that mostly is not the case. Behind the slim belt of mangroves, one finds some of the most intensively used agricultural lands. The mangroves are an important local resource as they sustain significant harvest of wood and wildlife and provide important environmental services. The mangroves are nursery ground for important fisheries and shrimps, but also reduce coastal flood and storm damage and help filter sediments away from waterways. If properly managed, mangroves can provide timber for construction, charcoal for energy, food for livestock, shellfish for local consumption, and so on. Studies from The Gambia show that while the increment, or production of biomass, of the mangroves is almost three times as much as the increment of other closed forests. Lately, also the value of the mangroves for tourism has been discovered. Senegal in particular has known to appreciate this resource. Two national parks are based on the mangrove resource, Parc National du Delta du Saloum and Parc National de la Basse Casamance. The Casamance park is located close to the tourist center Cap Skirring and with its over 200 species of sea birds, it is a popular resort for photo safaris. For Western African countries, poor of lions and elephants, this is a major resource when it comes to eco-tourism. Environmentally seen, mangroves are one of the most valuable forms of wetlands worldwide, and one of the most threatened, suffering heavy losses in Asia, Latin America and Western Africa. "West Africa has many endemic plants and animals," professor Malcolm confirms. The mangroves are especially noted for their rare and threatened marine mammals, a large range of water birds, crabs and mangrove trees with air roots. Human exploitation of the mangroves have already paid a heavy toll on this habitat. Notably, mangroves have been cleared to build shrimp ponds, human infrastructure and fuelwood and much has been lost due to pollution. There has been done remarkably little research on the effects of global warming in Africa (and the tropics in general), compared to the amount of research done in temperate zones. "I know of only a handful of African studies, but very many temperate studies," Malcolm says. Meanwhile, the African mangroves continue to disappear due to exploitation and poor management. Global warming will pay its toll, and a rising sea level would eliminate the vast majority of the biotope. Small countries such as Guinea-Bissau and The Gambia stand at risk loosing a significant part of their territory as consequence of the projected rising sea level. Several developing countries, most notably Pacific Ocean states risking to lose all their territory, have protested sharply against the global warming, mostly the responsibility of the world's richest countries and their consumption of fossil fuels.
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