CARBON-SOURCES AND SINKS IN FOREST BIOMES OF THE FORMER SOVIET-UNION

The carbon budget of the forest biomes of the former Soviet Union (FSU ) and their sequestration potential were assessed by considering (1) n et ecosystem productivity (NEP) of different age forest stands and act ual forest coverage, (2) carbon flux related to forest fires, (3) the rate of peat accumulation, and (4) anthropogenic influences. The area of forest biomes in the FSU was estimated at 1426.1 million hectares ( Mha); forest ecosystems comprised 799.9 Mha, nonforest ecosystems and arable land comprised 506.3 and 119.9 Mha, respectively. The vegetatio n pool (phytomass and coarse woody debris) was 68.7 Gt C (carbon). The litter and soil carbon pools were 12.2 and 319.1 Gt C, respectively. The net primary productivity (NPP) of forest biomes ecosystems was 5.6 Gt C/yr, the rate of foliage formation was 2.3 Gt C/yr, the rate of h umus formation was 161 Mt C/yr with 73 Mt C/yr in the stable form. The NEP of the forest biomes was assessed from the data on NEP of young, middle-age, and premature forest stands. The NEP of the forest biomes was 825 Mt C/yr. Peat was accumulating at an average rate of 23 Mt C/y r. Carbon effluxes from mort-mass, litter, and soil organic matter dec omposition were calculated from the NPP, NEP, foliage, and humus forma tion rates. The efflux from mortmass decomposition was 2.6 Gt C/yr, fr om litter decomposition 2.1 Gt C/yr, and from soil organic matter deco mposition 61 Mt C/yr. Peat combustion represented a carbon efflux of 3 0 Mt C/yr. The carbon efflux from forest fires and agricultural activi ties was 199 and 10 Mt C/yr, respectively. Carbon efflux from wood har vesting (carbon sequestration in regrowing vegetation was excluded) wa s 152 Mt C/yr. Considering all components of the natural carbon cycle and the anthropogenic influences, FSU forest biomes were a net sink of 485 Mt C/yr of atmospheric carbon. The Siberian and Far East forests represent approximately 82% of the net sink. The total carbon sink in FSU forests was equivalent to one half of the annual CO2 fossil fuel e missions in the FSU or one half the carbon released from deforestation in subtropical regions.