Young forest ecosystems has special importance in the investigation of the global role of forests in the carbon balance because they accumulate carbon in their own biomass and as result of unbalancing of input and decomposition processes in soil.

Our research was conducted on the exceptional object: the long-standing experiment with forest stands of 6 main forest-forming species in Siberia. The forest stands of Siberian pine, pine, larch, spruce, aspen and birch were planted on the previously prepared old- arable dark-grey forest cryptopodzolic soil on 1971-72 years. Before they were planted and during growing and development the carbon storage was defined in all components of this ecosystems. It allowed estimate its influence to the carbon balance in the soil system. The same soil and hydrothermal conditions for development of these ecosystems allow us to say about influence of different tree species to the carbon flows in the soil.

Now all investigated forests has developed forest litter. For the last 25 years the soil system had accumulate 6.8-12.6 tC/ha as a humus matter. From 18-19 tC/ha under deciduous forests to 22-28 tC/ha under coniferous stands was accumulated in the light-mineralized organic matter on the soil surface and into its depth (0-20cm).

The mineralization flow to the atmosphere as CO2 makes up 72-88% of decomposition losses. Only 2.0-6.7% of decomposing matter takes part in the forming of humus matter. The correlation between input – decomposition – accumulation processes in the 25 years old forest ecosystems lead to the annual conservation in the ecosystems of 19-68% of carbon input. The prevalent form of accumulation is organic matter of plant residues. The rate of new humus fixation in soil makes up 4.3-15.0% of annual carbon input or 1.4-5.5% of carbon storage in the decomposing plant residues.

Thus, the soil system of 25-years old forest ecosystems accumulates 0.31-1.45 tC/ha per year. It makes up 20.1-47.5% of total annual accumulation in these ecosystems.