To be able to quantify the gains in CO2, afforestation must be practised on land deforested since at least 1990. Such areas are abundant in the boreal forest. In Quebec, about 1.7 million hectares of the commercial boreal forest are open forest spruce-moss stands.
It is believed that Canada's forest can support 2,000 trees per hectare. However, this isn't ideal. There's also land that has become unsuitable for agriculture, which is much more productive although it covers far fewer hectares. Municipalities also have areas that could be advantageously reforested.
However, we must be careful and think long term. If we plant a tree today, the carbon stock will be built up over time, with the growth curve having a maximum capture period. Then, the carbon will have to remain stored for 100 years. So, we have to think about species that live a long time.
It's important to keep in mind that if two billion trees were planted in Canada today, the maximum uptake of CO2 would occur between 2040 and 2080. Assuming a maximum uptake of two kilograms for the least productive species to 10 kilograms for the most productive species, planting two billion trees would at best remove a maximum of 5 to 10 million tonnes of CO2 per year from the atmosphere, which would be equivalent to the total emissions from Canada's aluminum smelters.
It's a relatively minor annual contribution—