* For a graphic please double click on http://tmsnrt.rs/2ijODTO
By Ed Stoddard
JOHANNESBURG, Jan 11 (Reuters) - Scientists say a recently discovered area of peatland straddling the two Congos contains 30 billion tonnes of carbon dioxide, equivalent to 20 years of U.S. greenhouse gas emissions, and must be protected to prevent major environmental damage.
The British and Congolese teams, who made the discovery in 2014, say it is the largest known tropical peatland - home to rare gorillas and forest elephants - and in Wednesday's edition of Nature they say development there would release the gas.
Carbon dioxide is linked to climate change and peatlands, formed from the accumulation of dead plant material, act as "carbon sinks." Peat does not decompose in a water-logged state but when it dries, the organisms that break down plant material revive and the carbon seeps back into the atmosphere.
"Peatlands are only a resource in the fight against climate change when left intact, and so maintaining large stores of carbon in undisturbed peatlands should be a priority," Leeds University ecologist and one of the study's authors, Simon Lewis, said.
The heavily forested and swampy terrain has kept development to a minimum - there is virtually no mining activity - but scientists say similar peatlands in rugged parts of Indonesia have been threatened by agriculture.
"It's very remote but what we've seen in south-east Asia is that these once-remote areas have been dried out and converted to oil palm plantations and rice plantations and other forms of industrial agriculture causing a huge release of carbon dioxide into the atmosphere," Lewis told Reuters.
The researchers combined space-age technology with old-fashioned exploration both to discover and to map the area. They used satellite imagery as well as slogging into the swamps and drilled by hand with coring devices to collect samples and identify the peat.
Seen from above, the swamp unfurls into a leaf-like shape from the Congo River into the northeast of the Republic of Congo and the remote western reaches of the Democratic Republic of Congo.
(Editing by Louise Ireland)