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Although carbon reserves in other types of tropical wetland forest have been assessed, the amount of carbon in mangroves has been largely
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The brackish tidal waters in which the trees thrive are a natural nursery for dozens of species of fish and shrimp essential to commercial fisheries around the world. Mangroves, also, offer protection from deadly storm surges from hurricanes and cyclones. Cyclone Nargis, which killed 138,000 people in Myanmar in 2008, would have been less deadly, experts say, if half the country's mangroves had not been ripped up for wood or to make way for shrimp farms. Overall, mangroves benefit the ecosystem by about 1.6 billion dollars a year.
Mangroves can sequester more carbon than an average tree in a tropical rainforest because of the soil they grow in. Mangroves grow in deep soils that are on average five times larger than other forests soils in the
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To estimate the abundance of carbon in mangroves, lead investigator J. Boone Kauffman, an ecologist at the Northern Research Station of the US Forest Service in Durham, New Hampshire, and his team sampled 25 mangrove sites across a broad territory of the Indo-Pacific region that included Micronesia, Indonesia and Bangladesh. This area spans 30 degrees of latitude and 73 degrees of longitude and represents about 40% of the global area covered by these trees. Mangroves grow in 118 countries, but the region the scientists chose has the greatest mangrove area and diversity.
Sludge stores
Kauffman and his team assessed above-ground and below-ground
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The team found that this underground layer is thicker in mangrove forests in estuaries than in those near the ocean, accounting for more than 70% of total carbon stores in estuarine mangroves and upwards of 50% in those in oceanic zones.
By combining their findings with global data, the researchers predict that worldwide carbon reserves in mangrove forests may be as high as 25%
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"Mangroves are among the most carbon-rich forests in the tropics," Donato and his colleagues said in the study, published in Nature Geoscience. "Our data show that discussion of the key role of tropical wetland forests in climate change could be broadened significantly to include mangroves."
Branching out
"This paper represents an important step forward in quantifying and
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However, the numbers still only represent rough estimates, owing to a lack of information about geographic variation in soil depth, the relative area of mangrove forests in estuaries compared with those near oceans, and the effect of land-use changes on carbon release from soils. They may even be overestimates, because "the authors seem to have sampled some of the largest, most robust stands around," says Thomas Smith, an ecologist at the US Geological Survey in St Petersburg, Florida.
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Still, the study could have a substantial impact on conservation efforts around the world, says Gail Chmura, an expert in coastal ecosystems at McGill University in Montreal, Canada. "Hopefully, it will help arguments to extend REDD+ to mangroves," she says, referring to an international plan to pay developing countries to preserve forests in a bid to help reduce global carbon emissions.
Robert Jackson, an ecologist at Duke University in Durham, North Carolina, agrees with Chmura, adding: "Mangrove forests are important for diversity, for coastal stability and for carbon, based on this paper. It gives another justification for preserving mangrove forests."
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Currently, less than 7% of the world's mangroves are under legal protection.
Source:
AFP,"Declining mangroves shield against global warming", accessed April 7, 2011
Nature,"Carbon-rich mangroves ripe for conservation",by Janelle Weaver, accessed April 7, 2011
Mongobay.com,"Vanishing mangroves are carbon sequestration powerhouses", accessed April 7, 2011
IOL Scitech,"Mangroves store climate-warming carbon", accessed April 7, 2011
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