Changing stock of biomass carbon in a boreal forest over 93 years

The growing stock more than doubled from 1.6 to 3.4 million m3 between 1912 and 2005 in forests on an area of 387 km2 in southern Finland. The stock expansion continued for 93 years noting interim results, which were available for 1959, 1982, 1994 and 1999. Forested area in the region hardly changed. Carbon sequestration was mainly a result of a long-term recovery from forest degradation, a legacy of land use in the 18th and 19th centuries. Tree demography responded to management change especially of mature stands: Average tree size and stocking density of stands increased. On average the expanding biomass stock sequestered 18 tons C annually per km2 (18 g C per m2). In comparison, the emissions of fossil carbon in the region were estimated at 12 tons C per km2 (12 g C per m2) on average. However, fossil CO2 emissions exceeded biomass sequestration in recent decades. The powerful and persistent expansion of the carbon stock was an unintended co-benefit of forestry, which was motivated by the intention to improve timber yield. On the more negative side the change in management introduced clear-cuts, and a loss of diverse elements of the pre-industrial biota.