Under the hot July sun, four forestry interns sink their teeth into fieldwork. In fact, they bite into the ground, with shovels, to dig small holes and plant 2000 spruce shoots there, which, as they grow, will offset tens of tons of carbon.
“Gang! You will be able to bring your girlfriends, your buddies and your children here, one day, and tell them that you have contributed. This is why I insist so much on quality. We do this so that it lasts in the long term,” shouts Jean-François Lamarre, the developer of the Montmorency forest, a vast area located 75 km north of Quebec.
Planting trees is nowadays an ultra-common approach to sucking carbon from the atmosphere and thereby reducing the intensity of climate change caused by mankind’s fossil fuel habits. However, the effectiveness of planting depends on several factors that are still poorly understood by scientists.
“We can’t be against planting trees, but we have to plant them in the right place and in the right way,” says Évelyne Thiffault, a Université Laval professor specializing in forest carbon, in an interview.
The Montmorency Forest — a teaching and research forest managed by Laval University — is Ms.me Thiffault. His graduate students will precisely check this summer that the trees planted there in 2017 are doing their job well, in order to confirm the hypotheses made at the time in terms of carbon sequestration.
To achieve this, the student-researchers will measure the diameter of tree trunks, assess their height, identify forest residues on the ground and take soil samples for laboratory analysis. The sum of the different stocks will then make it possible to determine the quantity of carbon per hectare.
The four apprentices, soon to become forestry engineers, are taking part in a new phase of the carbon capture project at the former site of Camp Talbot, a forestry camp that was large enough to accommodate 50 people.
“This land had been abandoned for a few years,” explains Gabriel Bolduc, one of the trainees, under his mosquito net. Because of the embankment and the passage of the ten wheels, the ground is very compact, it is not easy to dig. Besides, the hay competes with tree shoots, it will probably kill some of them. »
Draw in Abitibi
On this type of site, the forest would not have regained its rights on its own. A helping hand from planters is therefore beneficial. However, a study by M.me Thiffault published in the spring shows that, on other types of terrain, nature knows very well how to manage without help.
His research project, which dates back to the summer of 2019, was carried out on agricultural land in Abitibi cleared at the beginning of the 20th century.e century and abandoned a few decades later (a story witnessed by filmmaker Pierre Perrault’s “Cycle abitibien”). Some of the 49 sites considered had been planted; others had been left to fend for themselves. They are now all reclaimed by the forest.
And after 50 years, it’s a draw in terms of carbon: the two categories of forest store just as much. “It was a surprise for us! admits Mme Thiffault. Natural succession was not expected to be so vigorous and efficient on agricultural land. »
The explanation lies in the carbon stored in the soil. Prior to planting white spruce, the soils were scraped by machinery. This disturbance caused the loss (by leaching, for example) of tens of tons of carbon per hectare. The trees planted therefore had a considerable backlog to catch up on.
The implications are significant: if the federal government promises to plant two billion trees, it must choose its sites carefully. No need to pay to plant where nature will do the work anyway, argues Mme Thiffault.
“You have to be more precise [dans nos choix de sites], and that is correct. When engineers build bridges, they can’t build the same kind of bridges everywhere,” she explains.
Roots and microorganisms
Traveling the bumpy roads of the Montmorency forest in the company of Jean-François Lamarre, we have the chance to see a multitude of landscapes pass before our eyes. Clearcut parcels, partial cuts, mature forests, natural regrowth sectors, plantation sectors, etc.
In Quebec, the vast majority of tree plantations do not aim to store carbon. Rather, they are used to accelerate regrowth for the next cut. Since the wood is intended for harvesting, its carbon cannot be accounted for as an offset.
However, intelligent management of these plantations maximizes the amount of carbon sequestered in the forest — and therefore minimizes the amount that ends up in the atmosphere.
Mr. Lamarre, a forestry engineer also with a background in conservation biology, points to a forest planted several years ago, where the stems are extremely close together. “It’s a very tight planting,” he observes. Some trees will choke. What density should we aim for? That’s the kind of thing we’re going to test here. »
Another plot, cut in 2019, is invaded by raspberries. A lot of debris from the cut, such as branches, was left behind. To accelerate the regrowth, this corner of the forest will surely be “studded with spruce trees”, explains the developer. We then talk about planting a few trees, without disturbing the soil.
The issue of soils is central: in the boreal forest, they contain 50 to 75% of the carbon. This carbon comes partly from leaves and needles that fall to the ground, but mainly from substances secreted by roots and underground microorganisms.
“To maximize soil carbon storage, you need vegetation and roots. You shouldn’t see brown earth on the surface,” explains Véronique Rouleau, a doctoral student working for Professor Thiffault who studies carbon sequestration in the soil based on forest management practices.
Since boreal forest soils are already rich in carbon, “it’s easier to lose carbon than to gain it,” warns Ms.me Roll. To avoid losing it, we must choose practices that limit the physical disturbance of the soil as much as possible. And to try to gain it, you have to plant vegetation in “hugely disturbed” places, such as old mining sites.
Long-lasting wood products
In its latest report, the Intergovernmental Panel on Climate Change (IPCC) highlights that the land use and forestry sector can deliver “large scale” reductions in greenhouse gases, but cannot make up for inaction in other areas.
Experts add that wood products can advantageously replace materials whose production generates more carbon, such as steel and cement.
In the Montmorency forest, a wooden bridge demonstrates the potential of this noble material. Its elegant arch of black spruce — “one of the strongest fibers in the world,” according to Mr. Lamarre — supports the heavily laden trucks that pass there. If all goes as planned, it will sequester carbon for at least 100 years.
“The best machine for storing carbon, that’s it! exclaims Mr. Lamarre, pointing to the forest all around. Plus, it’s free and it helps us breathe fresh air. »