Soil carbon stores in Nordic well-drained forest soils - relationships with climate and texture class

Soil organic carbon (SOC) pools in forest floors and mineral soil to a depth of 100 cm were determined in 234 well-drained Nordic forest soils from latitude 55-68degrees-N, and longitude 6-28degrees-E. The data were compiled in a database of Nordic forest soils, from literature, and sources of validated data the authors had access to. The SOC pool increased with both mean annual temperature (MAT) and mean annual precipitation (MAP), and the increase with MAT was more pronounced for coarse-textured soils than for medium-textured soils. Soil organic carbon in fine-textured soils was not correlated with MAT and MAP. Differences between texture classes were mainly due to different carbon stores in the upper 40 cm of the mineral soil and in the forest floor. The emphasis on well-drained soils eliminated the impact of hampered decomposition in hydromorphic soils. Large carbon accumulation in such soils probably explains the negative relationship between SOC and temperature reported in other studies. The increase in SOC with temperature and precipitation is interpreted as an indirect effect of higher net primary production.