Mangroves excel at storing carbon

Tropical mangrove trees are better at storing carbon dioxide than most other forests, and cutting them down unleashes more greenhouse gas than deforestation elsewhere, say scientists.

Mangroves are so efficient at keeping carbon dioxide out of the atmosphere that when they are destroyed, they release as much as 10 per cent of all emissions worldwide attributable to deforestation - even though mangroves account for just 0.7 per cent of the tropical forest area, says researchers.

Daniel Donato, of the US Agriculture Department's Forest Service and lead author of a study published in the journal Nature Geoscience, says mangroves store two to four times the carbon that tropical rainforests do.

"Mangroves store a lot of carbon, much more so than most forests on Earth, on a per hectare basis," says Donato. "Since they store so much carbon, there's probably a lot being released from all the mangrove deforestation that's going on."

Mangroves live where many people want to live, along ocean coastlines in the tropics, and their areal extent - the amount of land they grow on - has declined by 30 per cent to 50 per cent over the last 50 years, the study found.

Coastal development, aquaculture and over-harvesting have all contributed to mangrove deforestation. Rising sea levels expected this century are also a threat, the study says.

Besides storing carbon, mangrove forests act as fisheries, keep sediment in place, produce fibre and protect inhabited areas against storms and tsunamis, the researchers say.

Coastal mangrove forests and the ecological services they provide could be gone in as little as 100 years, according to the researchers.

Part of the reason for mangroves' efficiency in keeping carbon locked away lies in their location in tidal zones, where their roots are often covered with sea water.

They need complex root systems to keep them breathing even when the tides come in, says Donato. This same complexity traps sediment that comes in from rivers and it builds up. ...

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