Аннотация:This paper discusses characteristics of biological cycle of 90Sr in the birch forests of Bryansk oblast in the long term after the Chernobyl fallout. It focuses on the specific activity and inventory levels of 90Sr in soil stratum, various structural elements and types of the tree and herb-prostrate shrub strata, higher fungi, and litter. It is shown that presently the major part of 90Sr in the contaminated birch forests of Bryansk Poles’e is concentrated in the soil (82.3%), of which about 71% is deposited in the mineral soil horizons. The biota accounts for as low as 17.7% of the total radionuclide inventory with maximum values in the tree stratum. The input from herbaceous–prostrate shrubby vegetation and higher fungi is small (<0.5%). In birch forests, 3.07 kBq/m2 90Sr is involved in the biological cycle, which accounts for approximately 3% of its total inventory in the biogeocenosis and roughly corresponds to the radioactive decay of this radionuclide. The 90Sr largely goes toward the formation of annual growth increment of the forest stand, while the contribution of higher fungi to the cycling exceeds the contribution of the herbaceous-prostrate shrubby stratum. Return of 90Sr to soil is lower (48.2%) than its fixation in annual biomass increase increment (51.8%).
