We evaluated the balance of production and decomposition in natural ecosystems of Pinus sylvestris, Larix sibirica and Betula pendulain the southern boreal forests of central Siberia, using the Yenisei transect. We also investigated whether anthropogenic disturbances (logging, fire and recreation pressure) influence the carbon budget. Pinus and Larix stands up to age class VI act as a net sink for atmospheric carbon. Mineralization rates in young Betulaforests exceed rates of uptake via photosynthesis assimilation. Old-growth stands of all three forest types are CO₂ sources to the atmosphere. The prevalence of old-growth Larix in the southern taiga suggests that Larix stands are a net source of CO₂. The CO₂ flux to the atmosphere exceeds the uptake of atmospheric carbon via photosynthesis by 0.23 t C.ha⁻¹.yr⁻¹ (47%). Betula and Pinus forests are net sinks, as photosynthesis exceeds respiration by 13% and 16% respectively. The total carbon flux from Pinus, Larix and Betula ecosystems to the atmosphere is 10 387 thousand tons C.yr⁻¹. Net Primary Production (0.935 t-C.ha⁻¹) exceeds carbon release from decomposition of labile and mobile soil organic matter (Rh) by 767 thousand tons C (0.064 t-C.ha⁻¹), so that these forests are net C-sinks. The emissions due to decomposition of slash (101 thousand tons C; 1.0%) and from fires (0.21%) are very small. The carbon balance of human-disturbed forests is significantly different. A sharp decrease in biomass stored in Pinus and Betula ecosystems leads to decreased production. As a result, the labile organic matter pool decreased by 6–8 times; course plant residues with a low decomposition rate thus dominate this pool. Annual carbon emissions to the atmosphere from these ecosystems are determined primarily by decomposing fresh litterfall. This source comprises 40–79% of the emissions from disturbed forests compared to only 13–28% in undisturbed forests. The ratio of emissions to production (NPP) is 20–30% in disturbed and 52–76% in undisturbed forests.

Abbreviations: LOM = Labile organic matter; MOM = mobile organic matter; NPP = Net primary production; Rh = Heterotrophic respiration; SOM = Soil organic matter.