CARBON STORAGE IN FOREST SOIL OF FINLAND .2. SIZE AND REGIONAL PATTERNS

For confidently estimating the amount of carbon stored in boreal fores t soil, better knowledge of smaller regions is needed,In order to esti mate the amount of soil C in forests on mineral soil in Finland, i.e. excluding peatland forests, and illustrate the regional patterns of th e storage, statistical models were first made for the C densities of t he organic and 0-1 m mineral soil layers. A forest type, which indicat ed site productivity, and the effective temperature sum were used as e xplanatory variables of the models, In addition, a constant C density was applied for the soil layer below the depth of 1 m on sorted sedime nts. Using these models the C densities were calculated for a total of 46673 sites of the National Forest Inventory (NFI). The amount of the soil C was then calculated in two ways: 1) weighting the C densities of the NFI sites by the land area represented by these sites and 2) in terpolating the C densities of the NFI sites for 4 ha blocks to cover the whole land area of Finland and summing up the blocks on forested m ineral soil. The soil C storage totalled 1109 Tg and 1315 Tg, when cal culated by the areal weighting and the interpolated blocks, respective ly. Of that storage, 28% was in the organic layer, 68% in the 0-1 m mi neral soil layer and 4% in the layer below 1 m. The total soil C equal s more than two times the amount of C in tree biomass and 20% of the a mount of C in peat in Finland. Soil C maps made using the interpolated blocks indicated that the largest soil C reserves are located in cent ral parts of southern Finland. The C storage of the organic layer was assessed to be overestimated at largest by 13% and that of the 0-1 m m ineral soil layer by 29%. The largest error in the organic layer estim ate is associated with the effects of forest harvesting and in the min eral soil estimate with the stone content of the soil.