The wood hiding the forest: the real carbon footprint of Quebec’s forestry sector

In Quebec and Canada, wood is often presented as a “green” material. Since trees capture CO₂ as they grow, wood from our forests is often described as a greener alternative to more energy-intensive materials, such as concrete or steel. This view has led some to argue that cutting down forests is even good for the environment¹.

But what does the scientific data reveal when we analyze the entire life cycle of forest products, from the harvesting of the trees to the end of life of the products made from them? A new animated video created as part of the Nature alliée initiative with input from several university partners specializing in the issue, presents a more complete portrait of the wood from our forests. The purpose of this video is to inform the public about the carbon dynamics associated with the entire life cycle of forest products.

Cutting down forests releases large amounts of carbon

In Quebec, the boreal forest provides the majority of commercial forest products. It is also one of the largest carbon pools in the world². Interestingly, nearly 80% of this carbon is stored in the soil, and can accumulate under vegetation for thousands of years³. However, the upper layers of the soil are more vulnerable to disturbance, and the passage of heavy machinery during logging may affect a forest’s storage capacity⁴. The best way to see the impact of tree harvesting machinery is to compare this forest under human disturbance with a forest of the same age that has remained intact.

Take, for example, a mature 80-year-old boreal forest covering an area of 2 hectares. On one side, one hectare of forest is clearcut, which is still the most common felling method in Canada⁵. This mature natural forest can store between 140 and 280 tonnes of carbon per hectare^6,7,8. Over time, the forest will continue to grow and increase its carbon stocks slowly until reaching a plateau at the old-growth forest stage around 100–140 years⁹ with a stock of up to 270–356 tonnes of carbon per hectare^10,11.

The cut area loses a significant portion of its stored carbon in the first few years after being cleared¹². For each tree cut, up to 50% of the tree’s total carbon is left in the forest as debris (branches, stump, etc.), and the other 50% is removed from the trunk¹³. Some of the carbon from the slash will be transferred to the soil carbon stock, while the rest will decompose within a period of few years (branches and debris) up to more than a decade (large pieces of wood)¹⁴, releasing CO₂ into the atmosphere. By removing the forest cover and compacting and mixing the soil through the use of heavy machinery, logging disturbs the organic layer of the soil and can expose the mineral layer, thereby accelerating the breakdown of organic matter¹⁵. According to Canada’s most recent national greenhouse gas inventory, logging alone emitted an average of over 70 million tonnes of CO₂ eq per year between 1990 and 2023¹⁶.

Some studies on the boreal forest show a decrease of more than 40% in total carbon stocks after logging, or nearly 90 tonnes per hectare¹⁷. As a result, a significant amount of carbon is removed from the forest, and it will usually take several decades for the new stand to rebuild the initial carbon stocks in the soil and vegetation. Studies in Quebec show that clearcut areas are net sources of carbon to the atmosphere for 15 to 20 years after cutting¹⁸. After 100 years, unmanaged natural forests store more carbon and continue to actively sequester compared to exploited forests¹⁹. This carbon debt between the two scenarios is estimated at 29 tonnes per hectare according to Giasson et al. (2023)²⁰.

Carbon release at the mill

Now let’s follow the log that is removed from the forest and taken to a sawmill or other processing plant. The trunk, which contains only about 50% of the carbon of the entire tree²¹, will be transformed into lumber. This process of transforming the trunk into lumber will extract another 29% of the tree’s carbon content from the tree by removing the bark (5%) and producing sawdust, shavings and chips (24%). In the end, the lumber will contain only 21% of the carbon of the original tree²².

Most of the by-products derived from the trunk residues will be burned or converted into short-lived products, such as pulp and paper. According to the IPCC, the average lifespan of a sheet of paper is two years, and its carbon content is quickly released into the atmosphere²³. According to Canada’s National Greenhouse Gas Inventory Report, nearly 70% of GHG emissions from end-of-life forest products come from the pulp and paper and bioenergy sectors²⁴. It is therefore important to understand that lumber does not come in a vacuum and that there is a “baggage of GHG emissions” associated with significant carbon losses from short-lived by-products from the same tree.

End of life of wood and return to atmosphere

Imagine a large carbon pool made up of all the products from our forests currently in use: framing, furniture, floors, panels, papers, cardboard, etc. According to the Canadian inventory, this pool had more than 620 million tonnes of carbon by 2023. Every year, new forest products are put on the market and enter this large pool, while old products become obsolete and are sent to the incinerator or landfill, thereby exiting this large carbon pool. On a Canada-wide basis, the end-of-life of forest products—in other words, their exit from the carbon pool—averaged 139 million tonnes of CO₂ eq annually between 1990 and 2023. By comparison, all light-duty gasoline vehicles in the country emitted 25 million tonnes of CO₂ eq in 2023. These emissions are based on a half-life time of 35 years for lumber and 25 years for particle board²⁵. For example, today’s emissions largely come from wood products manufactured decades ago. In the same way, products from our current forests will release their carbon into the atmosphere later this century.

While it is true that wood stores carbon, it is equally true that this carbon is only temporarily stored. Just how that carbon is released into the atmosphere will have a big impact on the climate. For example, when wood breaks down in landfills, a significant portion of its carbon will be emitted as methane, a greenhouse gas that is about 25 times more potent than CO₂ over a 100-year period. According to the IPCC, 50% of the carbon of decomposing wood in landfills will be released as methane and the other 50% as CO₂²⁶. However, given that certain Quebec landfills capture methane for energy use, Moreau et al. (2023) estimates that methane will make up 33% of the carbon released from decomposed wood²⁷.

Some perspective needed when using wood as a substitute

It is true that wood can replace more polluting materials, such as concrete or steel. This is called the “substitution effect”. By adding a climate benefit to a wood product when it replaces a material that is more harmful to the environment, the substitution effect shortens the time it takes to pay the carbon debt associated with forest emissions and landfill. However, according research by Moreau et al., even when wood replaces concrete or steel, it takes about 60 years to offset large forest emissions²⁸. This means that if a forest is harvested so that its wood can replace concrete, rather than letting it continue to capture carbon, there will be a negative impact on the climate for at least 60 years before it starts offering benefits to the atmosphere. In the words of the study’s principal investigator, “we are far from a green revolution.”²⁹

It is also important to note that the vast majority of wood currently used does not replace other more polluting materials³⁰. For example, house framing—which accounts for a significant portion of the wood used in the market—is traditionally made of wood. There is therefore no substitution here, only continuity in usage. Finally, it is important to remember that most of the wood harvested is not used for long-life products, but rather for short-term uses. In other words, the potential for substitution remains very limited and is not sufficient to justify an increase in logging.

Conclusion

Wood is not inherently bad. But over its entire industrial life cycle, its exploitation contributes significantly to GHG emissions. Logging has direct and immediate impacts on the climate, while the benefits of wood use will take decades to materialize. In contrast, an intact forest continues to sequester carbon every year, in some cases for centuries. It is therefore essential to measure the climate impact of the forest sector as a whole, taking into account the entire life cycle of wood products, if we are to foster better practices, make informed choices about the future of our forests, and use the best tools available to combat the climate crisis.

1. Maïté Blanchette-Vézina- Députée de Rimouski à l’Assemblée nationale, ministre des Ressources Naturelles et des Forêts. 14 avril 2025. https://www.facebook.com/share/p/1CDrKtfiBU/  ↩︎
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