Maple trees shown to emit methane
By Chad Ingram
When one thinks of methane emissions, a herd of livestock may come to mind more so than a grove of maple trees, however, a project by a University of Toronto researcher is demonstrating that maple trees do emit quantities of the greenhouse gas into the air.
Adam Gorgolewski, a U of T PhD candidate, presented his findings at a Celebration of Research at Haliburton Forest on May 10. The annual event provides an opportunity for those conducting scientific research on the forest property to share their work.
Methane is a greenhouse gas, much more destructive in its properties than carbon dioxide. Forty kilograms of methane is the equivalent of more than a ton of the latter.
“It’s a much more potent greenhouse gas,” Gorgolewski said, adding methane is responsible for approximately 20 per cent of human-caused global warming.
Some living trees do emit relatively small amounts of methane, commonly through their trunks, but, as Gorgolewski explained, to his knowledge, there’d been no research done on methane fluxes from sugar maple trees in Canada.
Gorgolewski explained he set about to answer three questions with his research: 1. Do sugar maples emit methane? 2. What about their branches, twigs and leaves? 3. Is methane emitted when maple trees are cut down?
Armed with highly specialized equipment including a greenhouse gas analyzer, Gorgolewski took data from numerous maples on the forest property, and determined that yes, living sugar maples are emitting methane into the air through their trunks. Healthier trees produce less methane than unhealthy ones, and for trees with wounds on them, “wounds are clearly emitting a lot of methane, compared to other parts of the tree,” Gorgolewski said.
He also found that, in addition to their trunks, maples are emitting methane through their branches and twigs, and that saplings also produce methane, albeit in much smaller quantities than grown trees.
Interestingly, his research showed that maple leaves actually absorb methane, meaning they are what is known as a “methane sink.”
“The rest of the tree is emitting it, but the leaves are absorbing it,” Gorgolewski said. “ . . . Maple foliage is a methane sink, but all the other components of the maple appear to be emitting methane.”
Perhaps also surprising is what is essentially a plume of methane that is released from a maple tree when it is cut down, the gas essentially having been bottled up within the body of the tree.
“Harvesting does cause a pulse of methane emissions from the trees,” Gorgolewski said, adding, “this is really a strikingly large amount of methane emissions.”
He also found that, while levels are lower, maple trees continue to emit methane during the winter months.
U of T PhD student Juliana Vantellingen also studies methane emissions and shared the results of her research, which looks at the effects of forestry on the methane in soil.
“Soil both produces and absorbs methane,” Vantellingen explained, adding this is due to two separate microbial communities that make their homes in the earth. Methanogens are microorganisms that produce methane and are found in wetter soils or deeper in the earth, and methantrophs are microorganisms that absorb methane, and are found in drier soils. As Vantellingen explained, the two groups can co-exist in one soil profile, so a section of earth can be both producing and absorbing methane simultaneously.
In general, soils in temperate Ontario forests are sinks, meaning on the whole, they absorb methane.
Vantellingen’s research examined the impact of repeated traffic by heavy forestry equipment, such as cable skidders, on the methane fluxes in soil within forestry cut blocks. As Vantellingen explained, the treads from machinery turn up the soil, then compact it, making it more likely to become wet, and therefore more likely to become suitable for methanogens, which emit methane. So, essentially, does the repeated disruption and compaction of soil along skid trails turn it from a methane sink, to a methane source?
While the research showed some evidence of this phenomenon occurring in the soil, overall, it is likely not a cause for great concern when it comes to climate change implications.
As Vantellingen explained, the methane emitted from the soils of skid trails within one-year-old cut blocks within Haliburton Forest would likely total the equivalent of about one ton of carbon dioxide per day.
“That seems pretty bad, but you have to account for all the other soil surrounding these skid trails,” she said.
The calculations she presented assumed that skid trails comprise 15 per cent of the soil within a forestry cut block.
“That means there’s 85 per cent other soil that hasn’t been run over by a skidder,” she said. Her research shows that about 90 per cent of the methane being produced by skid trails within cut blocks is being absorbed by the remaining soil within those cut blocks.
So, the cut blocks themselves are still ultimately sources of methane, however, the bulk of that methane is being absorbed by the soils that have not been disrupted by machinery.
On top of that, there are the forested areas surrounding the cut blocks themselves.
“There is tons of other forest that isn’t even touched, and these are all methane sinks,” Vantellingen said. “So, when you start scaling even bigger, outside of your cut blocks, even when you look at all of those areas that are emitting methane in the five years since harvest, it is absolutely swamped by all the forest that is untouched and consuming methane on a daily basis.”