ENVIRONMENT: Mangroves, much more than a swamp
Mangroves a "must-have" along the coast
Johannesburg, 15 July 2010 (IRIN) - On 26 December 2004 an undersea earthquake off Sumatra - one of the most powerful ever recorded - generated a tsunami that rolled across the Indian Ocean and surged onto the shores of southeast Asia with outrageous force. Coastlines protected by mangroves were the lucky ones. Or were they?
After the tsunami most disaster experts put mangrove forests on the list of "must-haves" for communities living along the coast; they bore the brunt of tidal waves, protecting people, animals, homes and livelihoods, and helped disperse the force of rushing water.
But the benefits of mangroves were soon caught up in a battle of studies. The main protagonists were researchers Jeff Vincent, from Duke University in the US, and Saudamini Das, from the University of Delhi in India, on one side, and a group from Australia, India and Guam on the other.
Das and Vincent studied villages hit by a cyclone in 1999 in the Indian coastal state of Orissa and were the first to show that mangroves could offer protection from certain types of disasters. Their work was published in The Proceedings of the National Academy of Sciences.
Andrew Baird of the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Australia, Ravi Bhalla and V. Srinivas of the Foundation for Ecological Research, Advocacy and Learning in India, and Alexander Kerr of the University of Guam, said: "It would be extremely dangerous to rely on tree planting alone to shield coastal communities in the event of future tsunami or storm surges, and doing so could lead to further tragedies."
Now, the first global assessment of mangroves in a decade has appeared, and it takes a middle-of-the road stand on the benefits of mangroves as a protective measure against storms and tidal surges.
||A mangrove is a tree or shrub that grows in tidal, chiefly tropical, coastal swamps having numerous tangled roots that grow above ground and form dense thickets
||There are 70 species of mangrove
||The countries with the
largest mangrove areas are Indonesia with 21 per cent of global mangroves, Brazil with 9 per cent, Australia 7 per cent, Mexico 5 per cent and Nigeria with 5 per cent
|Source: The Atlas & various
"Mangroves are not a panacea; mangroves cannot provide much of a buffer against tidal waves which are more than 15 metres high," acknowledged Mark Spalding, a marine ecologist at The Nature Conservancy, a UK-based NGO. "But that is not to say they do not act as a buffer - often it is the only thing communities have protecting them from the sea."
Spalding is the lead author of the World Mangrove Atlas, which covers 123 countries and is billed as the most comprehensive assessment ever. He is enthusiastic about the role of mangroves in the unfolding impact of climate change. "It provides one of the best kinds of adaptation for coastal communities, who not only face more intense cyclones but sea-level rise."
Like other trees, mangroves soak up harmful carbon dioxide from the atmosphere, and store the carbon in the wood; when they die the carbon is trapped in the water-logged soil. "Unlike peatlands, [one of the most effective carbon stores of all ecosystems] you don't face the threat of methane emissions," Spalding noted.
Methane gas released from peat bogs in the northern third of the globe probably helped fuel the last major round of global warming, ending the last ice age between 11,000 and 12,000 years ago, a joint study by the University of California and the Russian Academy of Sciences concluded.
A UN Environment Programme assessment in 2009 found that worldwide, mangroves probably sequester carbon faster than terrestrial forests; the bad news is that mangroves are being lost three to four times faster than land-based forests, and about one-fifth of all mangroves have disappeared since 1980, according to the Atlas.
Restoring mangroves is also not always easy. Community-driven projects were often more effective, because "The big [internationally funded] projects got the species wrong," Spalding said. The Philippines has made tremendous strides in improving mangrove coverage with new policies and projects driven by local government.
Many countries, such as Mexico, Belize, Tanzania and Mozambique, have established general legal protection for mangroves, controlling destructive activities by means of strict licensing systems.
The Atlas, published by Earthscan, is a joint project by the International Tropical Timber Organization (ITTO), the International Society of Mangrove Ecosystems, the UN Food and Agriculture Organization, UNEP-World Conservation Monitoring Centre (UNEP-WCMC), UNESCO - Man and Biosphere (UNESCO-MAB), the UN University Institute for Water Environment and Health (UNU-INWEH) and The Nature Conservancy (TNC).