Radial Growth Response of Scots Pine (Pinus sylvestris) to a Gradient of Radioactive Contamination

Scots pine (Pinus sylvestris) tree rings exhibit a pronounced response to high doses of ionizing radiation, resulting in the development of a “dose-radial growth response” model of particular interest. This study analyzed the radial growth of 50 pine trees within the East Ural Radioactive Trace (EURT) zone that was formed in the autumn of 1957 as a result of the Kyshtym accident. Cores from 34 trees growing at two sites with low levels of radioactive contamination were used as the control group. A decrease in the radial growth index of Scots pine within the EURT was observed from 1959 to 1962, i.e., 2 to 5 years after the Kyshtym accident. The magnitude of this decrease was directly proportional to the soil 90Sr contamination density at the tree’s location. The EURT zone, where a radial growth response was detected, was very narrow (approximately 300 m wide). The initial (highest) dose rate range at which trees showed a response was between 0.62 and 4.23 Gy day–1, spanning less than one order of magnitude. At higher dose rates, tree mortality was observed, whereas at lower doses, their radial growth was comparable to that observed at the control sites. The best model to describe the relationship between the radial growth index of Scots pine and the density of radioactive soil contamination near the trunk was developed for the 1959–1960 growth index. The coefficient of determination (R 2) for this linear regression model was 0.69.