Washington, Aug 9 (IANS): Diseased forest trees, aged between 80 to 100 years and infected by fungii, may be a significant new source of methane that causes climate change, according to US researchers.

Sixty trees sampled at Yale Myers forest contained concentrations of methane that were as high as 80,000 times ambient levels. Normal air concentrations are less than two parts per million, but the Yale researchers found average levels of 15,000 parts per million inside trees.

"These are flammable concentrations," said Kristofer Covey, doctoral candidate at the Yale School of Forestry & Environmental Studies (YSF&ES), who led the study.

"Because the conditions thought to be driving this process are common throughout the world's forests, we believe we have found a globally significant new source of this potent greenhouse gas," added Covey, according to an YSF&ES statement.

The estimated emission rate from an upland site at the Yale forest is roughly equivalent to burning 40 gallons of fuel per hectare of forest per year.

It also has a global warming potential equivalent to 18 percent of the carbon being sequestered by these forests, reducing their climate benefit by nearly one-fifth.

"If we extrapolate these findings to forests globally, the methane produced in trees represents 10 percent of global emissions," said Xuhui Lee, study co-author and professor of meteorology at Yale. "We didn't know this pathway existed."

The trees producing methane are older, between 80 and 100 years old and diseased. Although outwardly healthy, they are being hollowed out by a common fungal infection that slowly eats through the trunk, creating conditions favourable to methane-producing micro-organisms called methanogens.

"No one until now has linked the idea that fungal rot of timber trees, a production problem in commercial forestry, might also present a problem for greenhouse gas and climate change mitigation," said Mark Bradford, study co-author and assistant professor of terrestrial ecosystem ecology at YSF&ES.