By Mark Kinver
Science and nature reporter, BBC News
Mangrove forests may have reduced the cyclone's impact, a politician says
Destruction of mangrove forests in Burma left coastal areas exposed to the devastating force of the weekend's cyclone, a top politician suggests.
ASEAN secretary-general Surin Pitsuwan said coastal developments had resulted in mangroves, which act as a natural defence against storms, being lost.
At least 22,000 people have died in the disaster, say state officials.
A study of the 2004 Asian tsunami found that areas near healthy mangroves suffered less damage and fewer deaths.
Mr Surin, speaking at a high-level meeting of the Association of South-East Asian Nations (ASEAN) in Singapore, said the combination of more people living in coastal areas and the loss of mangroves had exacerbated the tragedy.
MANGROVES - NATURAL DEFENCES
Mangroves are salt-tolerant evergreens that grow along coastlines, rivers and deltas
Found in more than 120 tropical and subtropical nations
The plants' root systems have been shown to dissipate wave energy
"Encroachment into mangrove forests, which used to serve as a buffer between the rising tide, between big waves and storms and residential areas; all those lands have been destroyed," the AFP news agency reported him as saying.
"Human beings are now direct victims of such natural forces."
His comments follow a news conference by Burma's minister for relief and resettlement, Maung Maung Swe, who said more deaths were caused by the cyclone's storm surge rather than the winds which reached 190km/h (120mph).
"The wave was up to 12ft (3.5m) high and it swept away and inundated half the houses in low-lying villages," the minister said. "They did not have anywhere to flee."
Mangroves have been long considered as "bio-guards" for coastal settlements.
A study published in December 2005 said healthy mangrove forests helped save Sri Lankan villagers during the Asian tsunami disaster, which claimed the lives of more than 200,000 people.
Researchers from IUCN, formerly known as the World Conservation Union, compared the death toll from two villages in Sri Lanka that were hit by the devastating giant waves.
The 2004 tsunami prompted a series of mangrove replanting projects
While two people died in the settlement with dense mangrove and scrub forest, up to 6,000 people lost their lives in a nearby village without similar vegetation.
"Mangroves are a very dense vegetation type that grows along the shore," explained Jeffrey McNeely, chief scientist for IUCN.
"Where the saltwater and freshwater meet, that is where the mangroves grow; they often extend from several hundred metres to a few kilometers inland.
"Especially in river deltas, mangroves prevent waves from damaging the more productive land that are further inland from the sea."
A recent global assessment found that 3.6 million hectares of mangrove forests had disappeared since 1980.
The study carried out by the UN Food and Agriculture Organization (FAO) said that Asia had suffered the greatest loss, with 1.9 million hectares being destroyed, primarily as a result of land use change.
It found that large-scale conversion of mangroves into shrimp and fish farms were among the main destructive drivers.
Other pressures included new development to accommodate the growth in the tourism sector and rising populations.
Mette Wilkie, a senior forestry officer for the FAO, said most of the mangroves in Burma had suffered as a result of being overexploited.
"There are very limited areas that you would describe as pristine or densely covered mangrove in the Irrawaddy area," she said, referring to the region of Burma where Cyclone Nargis first made landfall.
"There are some efforts in place to try to rehabilitate and replant mangroves, but we do know that the loss rate is quite substantial still.
"During the 1990s, they lost something like 2,000 hectares each year, which is about 0.3% being lost annually.
"But that does not give you the whole picture because the majority of these tidal habitats are being degraded, even if they are not being completely destroyed."
However, the global picture is not entirely bleak. The FAO assessment showed that the annual rate of destruction had slowed from 187,000 hectares during the 1980s to 102,000 hectares during the early 2000s.
Some nations, such as Bangladesh, had actually increased mangrove cover, the FAO reported.
The role mangroves can play in reducing the devastation caused by extreme weather events was among the reasons behind Bangladesh's decision to protect one of the world's largest examples of the coastal habitat.
The Sundarbans, located in the delta of the Ganges and Brahmaputra rivers, contain about 100,000 hectares of mangrove forest habitat.
"This has been allowed to grow, or in part at least, because Bangladesh was really hammered by a typhoon that killed something like 300,000 people a couple of decades ago," Dr McNeely said.
"They realised that if they did not have that mangrove buffer, another typhoon heading up the Bay of Bengal would cause even worse damage because the population is even more dense than it was then."