Abstract The results of the phytomass (live biomass) estimates inventory for the Siberian forests are presented. These results are based on the following: (i) models estimating basic phytomass fractions for eight main forest-forming species (pine, spruce, fir, larch, Russian cedar, birch, aspen, oak); (ii) an ecoregional division of the territory into 63 ecological regions; and (iii) data from the State Forest Account (SFA) of 1993. The models are in the form of multidimensional regression equations for the ratio R fr = M fr / GS , where M fr is the mass of a phytomass fraction in teragrams (Tg), and GS is (green) growing stock in cubic meters (m 3 ). The independent variables used are age, site index and relative stocking of stands. The fractions evaluated are wood and bark of the stems, bark, wood and bark of branches, foliage, stump and roots, understorey and green forest floor. The final results are presented by 18 administrative units and three economic regions. The total phytomass of the vegetation of forest ecosystems of the total forested areas in Siberia is estimated to be 48 253.8 Tg of dry organic matter, of which 59.2% are stems, 18.4% stump and roots, 8.4% branches, 5.6% green forest cover, 3.4% foliage, 2.1% understorey and an additional 2.9% of the total phytomass is in the form of shrubbery areas. Due to Russian forest terminology, forested areas, i.e. closed forests, include forests generated by: (i) so-called main forest-forming species combined in three groups (coniferous, hard-leaved deciduous and soft-leaved deciduous); (ii) other species (rare, valuable and introduced species) with small area; (iii) shrubbery areas, considered as forested areas for territories where forests are not able to grow due to severe climatic conditions (zonal and altitudinal tree lines). The average density of phytomass (as an average of the total forested areas) is 4.04 kg of carbon (C) per square meter and varies from 2.0 kg C/m 2 (in ecoregions of the forest tundra) to 5.7–5.9 kg C/m 2 (in southern taiga and mixed broadleaved coniferous forests in the Far East). The C dynamics over time that have been estimated based on official forest inventory data for 1961–1993 reveal that during this period the Siberian forests were, on average, a small source of C emissions (about 20 Tg C/year). For `reconstructed' dynamics of the growing stock, which take into account systematic errors in the forest inventory data, the Siberian forests were estimated on average to sequester carbon (51 Tg C/year). Both approaches provide the conclusion that during the 10 years between 1983 and 1992 the Siberian forests have been a net source of atmospheric carbon (between 81 and 123 Tg C/year).