And some argue that we should adjust forest management practices now to improve the odds.
“When you hear in the news how we’re trying to limit climate warming to 1.5 degrees Celsius, that warming projection is based on things like this forest carbon measurement that we take,” said Loïc D’Orangeville, one of several scientists who they collect data at the Acadia Research Forest off Route 10, north of Burpee Stream.
Wood is a “good, long-term” way to sequester carbon, said D’Orangeville, an associate professor in the faculty of forestry and environmental management at the University of New Brunswick.
Trees use energy from the sun and convert carbon dioxide and water into sugars, wood and oxygen.
All climate models assumed that with longer growing seasons, trees would grow more and, overall, forests would store more carbon, D’Orangeville said.
But his research suggests that may not be the case.
“It’s much more complicated than that,” he said.
In a paper published in the journal Nature in August, D’Orangeville and US colleagues report finding that trees in the research forests of Harvard University in Massachusetts and the Smithsonian Institution in Maryland no longer grew wood with longer growing seasons. long. The growing period just changed.
“If there was a warmer spring, they would start growing early in the season, but they would also stop growing early in the season.”
“This has been a big shift in our understanding, in my opinion,” D’Orangeville said.
“A certain level of heating may be good up to a point, and then that beneficial effect becomes harmful.”
“That study told us we may actually have passed that tipping point in those forests.”
According to D’Orangeville, the lesson is that we can’t assume the forest will adapt to climate change and “do the work for us.”
“We actually have to make sure that we reduce carbon emissions into the atmosphere,” he said.
But what’s happening in the Harvard and Smithsonian research forests isn’t necessarily what’s happening here.
Most of New Brunswick and all of Nova Scotia and Prince Edward Island have a forest type known as “Acadian”. It has some of the same trees that grow in the New England area where he conducted his studies — known as the “temperate” forest — and some of the trees that grow in the “boreal” forest that covers most of Canada. The Acadian forest also has a unique species – spruce.
Conversely, tree species in the boreal forest are expected to grow more with warming, D’Orangeville said, especially in eastern Canada, where water is abundant.
He expects future growth in the Acadian forest will vary between tree species, and has some experiments underway to get a better idea of how they’ll fare.
Balsam fir, which now dominates local forests, might grow a little better with warming, D’Orangeville said, but only up to a point.
“It will probably slow down eventually and then be replaced by other species.”
While D’Orangeville focuses on how individual trees grow and breathe, Manuel Helbig, his colleague in Dalhousie University’s physics and atmospheric sciences department, is one of the people looking at the bigger picture: how the forest as a whole is absorbing carbon and give it away.
A quarter of the carbon dioxide created by people ends up in the land, including forests, Helbig said.
“We want to understand exactly how much of that anthropogenic CO2 we’re emitting is going to end up in the forest, so that slows down climate change.”
“It can go both ways,” D’Orangeville said, because when leaves and wood decompose, for example, carbon dioxide is generated.
Scientists refer to the flow of carbon dioxide into and out of the forest as a “flux.” They’re measuring it in a handful of “flow towers” across the country.
Acadia Research Forest has the only flow tower in Atlantic Canada.
Instruments installed on the flow tower count CO2 molecules in the air above the treetops.
The UNB researchers started collecting this kind of data about a decade ago.
Helbig updated the equipment this fall to follow up on their work.
Interval sensors on the tower also measure temperature and humidity.
Helbig expects to find that the forest around Acadia’s flow tower is still absorbing CO2, but in smaller amounts during hot, dry summers.
It can also emit CO2 sometimes, he said, “if it’s really dry.”
Canadian forests are thought to have been net emitters of greenhouse gases due to disturbances for the last 15 years or so, D’Orangeville said, but we still have a “limited understanding” of how flux changes in response to heat, fires, droughts and insect infestation.
D’Orangeville would like to see many more flow towers to take measurements in different types of forest stands, some with more hardwood trees and some with younger and older trees.
He also thinks more studies of tree growth, such as the one described in his Nature paper, are worth doing.
He said the information was gathered using metal bands that cost about $15 each.
“It’s not a massive investment of money … but it ends up giving us critical information about the entire forest response.”
It could mean the difference, he said, between forest actively storing carbon or slowly dying.
In the meantime, he said, we should use the tools we have to help him.
“We plant millions of trees every year. The human power that’s out there in the woods … every day to manage the forest, we could use it to actually help the forest cope with climate change.”
“Things like increasing species diversity, that’s just like increasing your investment portfolio.”
This would help the industry, he said, and it would also help the environment.