August 8, 2012
New Source Of Climate Gas Coming From Diseased Trees
April Flowers for redOrbit.com - Your Universe Online
A new study from the Yale School of Forestry & Environmental Studies asserts that diseased trees may be a significant new source of methane gas that causes climate change.
The study, "Elevated Methane Concentrations in Trees of an Upland Forest," which will be published in Geophysical Research Letters sampled sixty trees at the Yale Myers Forest in northeastern Connecticut.
The Yale Myers Forest is 7,480 acres of mixed hardwood, pine and hemlock that has been managed continuously for over 75 years by the faculty and students at the Yale School of Forestry & Environmental Studies as an outdoor classroom and research facility.
The trees sampled contained concentrations of methane that were as high as 80,000 times ambient levels. Normal air concentrations are less than 2 parts per million, but the research team found average levels of 15,000 parts per million inside the trees.
"These are flammable concentrations," said Kristofer Covey, the study's lead author and a Ph.D. candidate at Yale. "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 estimated emission rate from an upland site at the Yale forest is roughly equivalent to burning 40 gallons of gasoline per hectare of forest per year. This reduces the climate benefit of carbon sequestration by nearly one-fifth, as the methane emission has a global warming potential equivalent to 18 percent of the carbon being drawn into these forests.
"If we extrapolate these findings to forests globally, the methane produced in trees represents 10 percent of global emissions," said Xuhui Lee, a co-author of the study and Sara Shallenberger Brown Professor of Meteorology at Yale. "We didn't know this pathway existed."
The trees that produce this methane are older and diseased. They range between 80 and 100 years old and look outwardly healthy. They are being hollowed out, however, by a common fungal infection that slowly eats through the trunk, creating conditions favorable for methane-producing microorganisms called methanogens.
Methanogens are common in wetlands, where they are responsible for marsh gasses and in the intestinal tracts of humans and ruminants, where they cause belching and flatulence. They also play a role in anaerobic wastewater treatments.
"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, a co-author and Assistant Professor of Terrestrial Ecosystem Ecology at F&ES.
Red maple, an abundant species in North America, had the highest methane concentrations. Other common species were not far behind, though, including oak, birch and pine. The rate of methane emissions was 3.1 times higher in summer, suggesting that higher temperatures may lead to increasing levels of forest methane. Since methane leads to higher temperatures, this is a rather vicious cycle.
"These findings suggest decay in living trees is important to biogeochemists and atmospheric scientists seeking to understand global greenhouse gas budgets and associated climate change," said Covey.