Ronald Reagan’s much maligned assertion in 1981 that: “Trees cause more pollution than automobiles do,” may have more truth to it than most folks imagined. Researchers at the Yale School of Forestry and Environmental Studies have discovered that trees right here in Connecticut that are diseased by fungi can emit high concentrations of methane – a greenhouse gas that plays a role in climate change.
But said lead author Kristofer Covey, a Ph.D. candidate who admitted his friends have been needling him about the Reagan connection, the methane isn’t completely negating the benefit trees, even diseased ones.
“The report’s pretty clear,” Covey said. “Methane being emitted is about 18 percent of the carbon being sequestered, which means these forests still provide climate amelioration.
“But not as large as we thought they were.”
Translation: The carbon reducing potential of these trees decreased by about one-fifth because of the methane. But there was still a substantial air quality net gain from trees.
Covey said researchers have known for a long time that trees can act like straws bringing methane up in soil water from wetlands. More recently, scientists also have begun to think that a stress reaction triggered by ultra violet light can also cause trees to produce methane. But this new finding in an upland forest in Union, Conn. was unexpected and in fact was found by accident.
One of Covey’s colleagues in the research was coring a tree in an oak forest when his students noted a hissing sound. Suspecting methane – which is highly flammable, students with him asked if it could be ignited, and indeed it could. That prompted this research during the winter and summer of 2011.
Sixty trees covering five different species were studied in the Yale Myers Forest. They were all 80 to 100 years old and while they appeared healthy, in fact suffered from a common fungal infection that essentially eats away the interior of the tree and creates process not unlike an anaerobic digester or digestion in a cow stomach.
Covey said the fungi start the wood decomposition and oxygen removal. Microorganisms called methanogens generate the methane. “Fungi are driving the process and these guys are batting cleanup,” he said.
Methane concentrations inside the trees ran as high as 15,000 parts per million as compared with fewer than 2 parts per million in normal air. Extrapolated across forests globally, that’s about 10 percent of worldwide emissions. But Covey cautioned that the team’s findings are not necessarily applicable elsewhere.
“That’s a tough call,” he said. “What’s driving it is common to forests worldwide. But it may vary widely.”
Covey expects methane production in internally decaying trees is likely site- and tree-specific and could vary greatly from location to location and with the trees age. Older trees are more susceptible to fungal infections and other diseases.
In the Yale forest, red maples were found to have the highest methane concentrations while oak, birch, hemlock and pine had lower levels. And methane emissions were more than three times greater in summer than in winter, so heat could turn out to be another factor.
Covey also said the Yale team’s findings don’t change the overall presence of greenhouse gases. “We haven’t really found new methane,” he said. “We already knew it was in the atmosphere. What we have found is that the arrows we’ve been drawing were in the wrong the place.
“We may have to revise the models.”
As for whether the old Reagan assertion has been proven. The team calculated the forest site it studied released methane roughly equivalent to burning 40 gallons of gasoline per every 2.5 acres per year. Which means trees have a way to go before they’re as polluting as most cars.
But Covey admitted he’s been concerned that his findings could be “taken in a crazy direction.
“It’s not case at all,” he said of any notion that trees are the climate change problem. “Trees are good for the world.”