Rehabilitation of tsunami affected mangroves needed
Should be part of integrated coastal area management
19 January 2005, Rome - Rehabilitation of severely affected mangroves would help speed up the recovery process from the tsunami, but large-scale planting should be undertaken with caution, the UN Food and Agriculture Organization (FAO) said today.
"Mangroves contribute directly to rural livelihoods by providing wood and non-wood forest products - including timber, poles, fuelwood and thatch for houses - and indirectly by providing spawning grounds and nutrients for fish and shellfish. Mangroves can also help protect coastal areas from future tidal waves," said Mette Løyche Wilkie, an FAO expert on mangroves.
Restoration of damaged mangroves should be undertaken as part of the post-tsunami rehabilitation process, but FAO does not recommend massive planting of mangroves in areas where they would replace other valuable ecosystems, such as turtle nesting grounds and sea grass beds.
According to FAO, rehabilitation and planting efforts should be undertaken within a larger framework of integrated coastal area management.
"The real issue is overall coastal management, not just the presence or absence of trees," said Patrick Durst, the senior forestry officer in the FAO regional office for Asia and the Pacific.
Management of mangroves and other vegetation is only one component of comprehensive coastal management, which also works to ensure appropriate development of fisheries and aquaculture, agriculture, roads and other infrastructure, industry, tourism and residential living areas.
Damage to mangroves and other coastal forests
Mangroves cover an area of around 15 million hectares (or 150 000 sq km) worldwide with close to 40 percent of this area found in the countries affected by the tsunami. As would be expected, mangroves and other coastal forests and trees were adversely affected by the recent tsunami.
The extent of the damage is still not clear and it may take some time before the final impacts are known, since the deposit of silt may clog the pores of the aerial roots of mangroves, and thus suffocate them. Changes in topography, soil salinity and freshwater in-flow from upstream may also adversely affect the mangroves and other coastal forests in the longer term.
"What we do know is that the demand for fuelwood, for wood to rebuild houses and infrastructure and for constructing fishing boats is substantial," said Jim Carle, an FAO expert on plantations.
"This is likely to lead to further pressure on the coastal forests, including mangroves," he said.
According to the most recent FAO assessments, more than 22 000 boats were destroyed in Sri Lanka, 5 264 in Thailand, 2 600 in three districts of Somalia and 1780 canoes in Nanggroe Aceh Darussalam and Nicas Island in Indonesia. Whereas most of the boats in Sri Lanka are made of fibreglass, many of the boats and canoes in other countries were made of wood.
FAO is working with several other organizations to gather information on the impacts of the tsunami on mangroves and other coastal forests and to provide advice to countries in their rehabilitation efforts.
Mangroves as barriers to tidal waves
"The role of mangroves in providing coastal protection against the actions of waves, wind and water currents is well known," Mette Løyche Wilkie said. "But the extent to which mangrove green belts contribute to saving lives against large tsunamis, such as the recent one in Asia, depends on several factors."
As widely reported, extensive areas of mangroves can reduce the loss of life and damage caused by tsunamis, but narrow mangrove strips can have limited positive effects, and in some cases the effects can even be negative.
During the recent tsunami, the Pichavaram mangrove forest in Tamil Nadu in India slowed down the waves, protecting around 1 700 people living in hamlets built inland between 100 to 1 000 meters from the mangroves. In Malaysia, in areas where the mangrove forests were intact, there was reduced damage, the Penang Inshore Fishermen Welfare Association observed. Officials in Sri Lanka made similar observations.
In Indonesia, the death toll in the island of Simeuleu, located close to the epicentre was relatively low, partly due to mangrove forests that surrounded the island.
On the other hand, narrow strips of mangroves, when uprooted or snapped off at mid-trunk and swept inland, can cause extensive property and life damage. At least in one reported case in Thailand they have also damaged shallow coral reefs.
"The protective effects of mangroves against tsunamis mainly depend on the scale of the tsunami and the width of the forest and, to a lesser extent, the height, density and species composition," Wilkie said.
A mangrove is a tree or shrub which grows in muddy, chiefly tropical, coastal swamps and has tangled roots that grow above ground.
Information Officer, FAO
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