Another is the permafrost reservoir, which is smaller than the active soil pool, but which is similar in size to the atmospheric carbon pool. (realclimate.org)
Nonetheless mature forests do play an important role in the global carbon cycle as stable carbon pools, and clearance of forests leads to an increase of atmospheric carbon dioxide levels. (sciencedaily.com)
About 2 - 3 times this much is tied up in roots and below ground carbon, which is a more difficult carbon pool to augment. (realclimate.org)