Canada's boreal forest, characterized by the predominance of conifers like pine and spruce, stretches in a vast curve across the country below the Arctic, from the Yukon territory in the northwest to the Atlantic coast of Newfoundland.
A 1993 study estimated it stored about 186 billion tonnes of carbon, equal to about 27 times what the world produces from burning fossil fuel each year.
Two-thirds of the carbon is stored in the forest's soil, which decays when the tree cover is removed.
Greenpeace says the carbon released as trees are harvested contributes to climate change. That, in turn, threatens the northern forest with problems such as insect outbreaks and increased forest fires that destroy more trees.
The global warming, which is often most apparent in the far north, also allows the permafrost to melt, releasing still more greenhouse gases.
Canada logging may ignite 'carbon bomb'