Global Forests, with a Focus on Boreal Forests

Globally, forests cover about 30% of the world’s land area but contain nearly 80% of the total terrestrial biomass. In humid conditions, annual dry matter production increases with increasing temperature from less than 2 Mg ha−1 yr.−1 in the boreal zone to more than 20 Mg ha−1 yr.−1 in the tropical zone. On a global scale, the total amount of carbon in forest ecosystems is 758 Gt. Boreal forests extend over Canada, China, Finland, Japan, Norway, Russia, Sweden, and the United States, where there are still large areas of unmanaged forest across the high-latitude regions. The mean carbon stock in boreal forests is 60–100 Mg C ha−1, i.e., 60–70% in the belowground biomass (roots and dead biomass), and the rest in the aboveground in living biomass of trees, shrubs, and ground vegetation. The mean carbon residence time in boreal forest is 100 years, but the decay rate varies depending on the temperature and moisture conditions.