Strategically planting trees along the northern edge of Canada’s boreal forest could remove multiple gigatonnes of carbon dioxide from the atmosphere by the end of the century, according to a new study led by researchers at the University of Waterloo.
The research, published in Communications Earth & Environment, provides one of the most detailed estimates to date of the carbon that could realistically be sequestered through reforestation and afforestation in northern Canada, accounting for fire, climate, vegetation loss, and land suitability.
Using satellite data and probabilistic modelling, the researchers found that planting trees on approximately 6.4 million hectares of land along the boreal–taiga boundary could remove roughly 3.9 gigatonnes of CO₂ by 2100. Expanding planting to all highly suitable areas increased the estimated removal potential to around 19 gigatonnes.
Canada currently emits just under 0.7 gigatonnes of CO₂ per year, meaning even the lower-end estimate represents several times the country’s annual emissions.
Modelling forests under real-world conditions
Large-scale tree planting has long been proposed as a climate solution in Canada, but until now there have been few spatially detailed, realistic estimates of what northern forests can actually deliver when ecological limits are considered.
The Waterloo study explicitly accounts for wildfire probability, climate variables, and the likelihood of early seedling mortality, all of which strongly influence whether planted forests survive long enough to store carbon over decades.
“We were surprised by how large the carbon-removal potential remained even with using conservative assumptions about available land and frequent fires,” said Kevin Dsouza, a postdoctoral researcher in the Department of Earth and Environmental Sciences at Waterloo and first author of the study.
The modelling shows that wildfire frequency is one of the most decisive factors shaping long-term carbon outcomes. Boreal ecosystems are naturally fire-adapted, but increasing fire activity under climate change can rapidly return stored carbon to the atmosphere, reducing the net benefit of planting.
“Fire frequency and early seedling mortality can make or break the benefits of tree planting,” Dsouza said.
Where trees are planted matters
One of the study’s clearest findings is that not all planting locations perform equally well.
The researchers found that replanting on historically forested land was far more effective at storing carbon than planting on areas that have long been non-forested, such as open tundra or grass-dominated landscapes.
“It was also striking that replanting on historically forested land was much more effective than planting on long-term non-forested areas,” Dsouza said. “That suggests that filling in the gaps in the northern forest is often smarter than converting open lands.”
These results highlight an important distinction often lost in public discussions of tree planting: reforestation and afforestation are not interchangeable. Sites that previously supported forests tend to have soils, microclimates, and ecological conditions that allow trees to survive, grow faster, and store more carbon over time.
Implications for Canada’s climate goals
Reducing greenhouse gas emissions remains essential to limiting the worst impacts of climate change. However, most climate pathways that meet international targets also rely on carbon dioxide removal to counterbalance hard-to-eliminate emissions.
The scale of carbon removal identified in the Waterloo study suggests that northern forest restoration could play a meaningful supporting role in Canada’s efforts to reach carbon neutrality by 2050 and meet its commitments under the Paris Climate Agreement—provided planting is targeted and sustained over the long term.
The findings also help explain why blanket tree-planting programs often struggle to deliver the climate benefits they promise.
“We recognize that Canada’s 2 Billion Trees program faced major implementation challenges,” Dsouza said. “That experience shows why successful climate-mitigation planting is about more than planting more trees, but about selecting the right sites, the right species mixes, and the right management approach to maximize long-term carbon and ecological outcomes.”
Ecological trade-offs still need study
While the study identifies substantial carbon gains, the authors emphasize that tree planting is not a one-dimensional solution. Further work will examine how new forests could affect permafrost stability and snow cover, both of which influence the amount of solar energy reflected back into space.
Planting trees in northern regions can darken the land surface, potentially increasing heat absorption if not carefully managed. As a result, climate-mitigation planting must balance carbon storage with broader ecosystem effects.
Interventions will also need to consider biodiversity, Indigenous priorities, and existing land uses, particularly in northern regions where landscapes support wildlife, cultural practices, and local economies.
“Well-planned afforestation can contribute to climate goals,” Dsouza said, “especially when it’s targeted, ecologically appropriate, and supported by long-term stewardship.”
A narrower but more durable role for forests
Rather than framing tree planting as a universal fix, the Waterloo study suggests a more focused role for forests in climate policy: targeted restoration at the boreal edge, guided by data on fire risk, land history, and long-term ecosystem behaviour.
By grounding its estimates in spatial detail and ecological realism, the research provides a clearer picture of where tree planting can deliver durable climate benefits—and where expectations should remain cautious.
The study, Substantial carbon removal capacity of Taiga reforestation and afforestation at Canada’s boreal edge, was conducted by researchers from Waterloo’s Faculty of Science and Faculty of Environment.
