Diseased trees in forests may be a significant unrealized source of the greenhouse gas methane that causes climate change, U.S. forestry scientists say. Sixty trees sampled in a forest in northeastern Connecticut contained concentrations of methane that were as high as 80,000 times ambient levels, Yale University researchers reported Tuesday. \"These are flammable concentrations,\" Yale doctoral candidate Kristofer Covey, the study\'s lead author, said. \"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.\" The trees producing methane are older, between 80 and 100 years old, and diseased, the researchers said. Although outwardly healthy, a common fungal infection is slowly easting through their trunks, creating conditions favorable to methane-producing microorganisms called methanogens, they said. \"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,\" study co-author Mark Bradford said. Red maple, an abundant species in North America, had the highest methane concentrations but other common species including oak, birch and pine were also producers of methane, researchers said. \"If we extrapolate these findings to forests globally, the methane produced in trees represents 10 percent of global emissions,\" study team member Xuhui Lee said. \"We didn\'t know this pathway existed.\"