DENSITY OF ORGANIC-CARBON IN SOIL AT CONIFEROUS FOREST SITES IN SOUTHERN FINLAND

More detailed knowledge of the density of organic carbon in soils of b oreal forests is needed for accurate estimates of the size of this C s tock. We investigated the effect of vegetation type and associated sit e fertility on the C density at 30 mature coniferous forest sites in s outhern Finland and evaluated the importance of deep layers to the tot al C store in the soil by extending the sampling at eight of the sites to the depth of ground water level (2.4-4.6 m). The C density in the organic horizon plus 1 m thick mineral soil layer ranged from 4.0 kg/m (2) to 11.9 kg/m(2), and, on the average, increased towards the more p roductive vegetation types. Between the depth of 1 m and the ground wa ter level the C density averaged 1.3-2.4 kg/m(2) at the studied vegeta tion types and these layers represented 18-28% of the total stock of C in the soil. The results emphasize the importance of also considering these deep layers to correctly estimate the total amount of C in thes e soils. At the least fertile sites the soil contained about 30% more C than phytomass, whereas at the more fertile sites the amount of C in soil was about 10% less than the amount bound in vegetation.