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Saving lives with mangroves

The tsunami of December 26, 2004 that killed tens of thousands may be viewed as a natural calamity beyond human management capabilities. But new scientific evidence suggests the loss of life could have been substantially mitigated. A research study reported by the journal Science presents the disturbing conclusion that the removal of mangroves from parts of the coastline in five Asian countries, including India, reduced protection available to communities living close to the coast when the waves struck. Some of the strongest proof of the protective effects of coastal vegetation has come from satellite imagery of Tamil Nadu's Cuddalore coast, pre- and post-tsunami. These images have led investigators, including experts from the University of Copenhagen, the M.S. Swaminathan Research Foundation in Chennai, the University of Cambridge, and organisations based in Japan, Malaysia, Indonesia and the United States, to conclude that villages located behind mangroves suffered little damage, while those without a natural shield were destroyed. Casuarina plantations along the coast raised years ago to shelter against cyclones also offered modest protection. Scientists from various countries who studied the Sri Lanka coast reported in Current Biology that relatively healthy mangroves in some of the 24 study sites had blunted the impact of the tsunami by dissipating the energy of its waves. An analytical model proposed by investigators based on tsunami-related data from Tamil Nadu suggests that the presence of 30 trees per 100 square metres may reduce the maximum flow pressure of the waves by better than 90 per cent. These important findings strengthen the view that low-cost natural defences provide a range of benefits that expensive human-made structures may not be able to match.

Given their importance as an ecosystem, it is tragic that coastal greenbelts are under increasing threat. Large swathes of mangroves that make communities resilient by serving as natural dykes and enhancing fish wealth by acting as breeding, spawning, and hatching grounds have been eliminated along many Asian coastlines for short-term economic gain. Dubious `environmental' policies drawn up to promote commerce at the cost of ecosystem have resulted in the loss of a quarter of the mangrove area in the five tsunami-hit Asian countries during the period 1980-2000. Globally, three million out of 18 million hectares of mangroves have been lost during the 1990s on account of facilitating settlements, tourism, industrial construction, and aquaculture. The recent research findings come as a timely warning. Clearly, there is no justification for dilution of environmental policy for immediate gains. Planting coastal vegetation, particularly mangroves, in appropriate locations to replace what has been lost could mitigate damage already done, but the real task before the Ministry of Environment and Forests is to strengthen the coastal regulation zone scheme to provide absolute protection to what is left of this ecosystem.

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