MAIN INVESTIGATION RESULTS ON THE FOREST RADIOECOLOGY IN THE KYSHTYM AND CHERNOBYL ACCIDENT ZONES

As a result of the long-term studies of radionuclide migration in fore st ecosystems in zones of radioactive contamination after the Kyshtym and Chernobyl accidents, the following trends were revealed: (1) High retention capacity of stand canopy with respect to radioactive fallout . This leads to high doses absorbed by apical and leaf meristems, beta -radiation giving the main part of the dose; (2) Fast self-decontamina tion of crowns during the growth period and relatively slow decontamin ation in the phase of physiological rest, regardless of amount of atmo spheric precipitation. The rate of crown decontamination determines th e value and duration of radiation stress on woody plants; (3) Accumula tion not less than 95% of the total radionuclide amount in the forest litter 1-2 years after the cessation of radioactive fallout; (4) Relat ively slow migration of strontium and cesium radionuclides along the f orest soil profile; (5) High capacity of the forest when serving as a biogeochemical barrier to the routes of horizontal and vertical radion uclide migration and export out of the zone of initial contamination, including migration into the river water; (6) Considerable difference between strontium and cesium when migrating in forest soils and in the soil-plant system; (7) Broad variations in transfer factors for uptak e of cesium-137 from soil into forest plants depending on the plant sp ecies and soil type. The primary radiobiological effects connected wit h irradiation of organisms are considered and secondary disturbances d ue to changes of ecological bonds between the components of irradiated forest ecosystem are discussed.