According to a new United Nations report, mangroves are being lost at a rate three to four times higher than land-based forests, with one fifth of all of the world's mangroves thought to have been lost in the past three decades.

Mangrove losses have slowed to 0.7 per cent annually, but the authors of the new atlas - the first global assessment of mangroves in more than a decade - warn that any further destruction due to shrimp farming and coastal development will result in significant economic and ecological declines.

Global mangrove forests are being lost up to four times faster than land forests, the first international assessment in more than a decade has shown. The World Atlas of Mangroves is the outcome of a five-year research collaboration headed by the United Nations Environment Program. It says about one-fifth of global mangroves have vanished since 1980; the present rate of loss is 0.7 per cent a year. The assessment estimates that close to 50,000 square kilometres, one-quarter of original mangrove cover, has been lost as a result of human intervention.

According to e previous study released by UNEP, mangroves, which inhabit fringe areas between fresh water and salt water systems, are mainly lost due to urban development or to make way for agriculture or aquaculture, such as shrimp farms.

Achim Steiner, executive director of the UNEP, highlighted the "immense costs those losses have had for people as well as nature", while pointing to the importance of conservation policies. "Together, science and economics can drive policy shifts - he said - Protected areas are now safeguarding around a quarter of remaining mangroves and many countries are now embarking on major restorations."

A new danger for mangroves could come from rising of sea levels. Mangroves follow seawater inland, posing a problem when urban areas get in the way.