Regression Modeling of the Radial Increment Dynamics in Scots Pine in Forests Contaminated with Radionuclides in Bryansk Oblast

Abstract

We study the dynamics of radial increment in Scots pine in the forests of Bryansk oblast contaminated with radionuclides after the Chernobyl disaster. We have developed regression models of the relationship between specific soil activity and the radial increment of trees for the transition stage of the disaster in 1987–1989 and four 5-year-long periods from 1990 to 2009, characterizing 20 years of the recovery period. We have found a strong positive correlation between the radial increment and specific soil activity. The correlation coefficients vary from 0.695 ± 0.198 to 0.895 ± 0.124 for early increment, and from 0.549 ± 0.231 to 0.937 ± 0.097 for late increment in different time periods. It is found that the cubic parabolic equation is the optimal statistical description of the relationship between the radial increment and concentration of radiocesium in soil. The minimal effective specific soil activity for the stimulation of radioactivity decreased from 25–26 kBq kg^–1 in 1987–1989 to 9–10 kBq kg^–1 in 2004–2009. The same value for the late increment varied from 20–21 to 16–17 kBq kg^–1 in the same periods. The maximal effective specific soil activity indicative of the highest effect of radiation decreased consequently from 110–120 kBq kg^–1 in 1987–1989 to 60–70 kBq kg^–1 in 2004–2009 for early increment. The same value for late increment varied in the same range with no tendencies in the same periods. Based on the model of radial increment dynamics, we assessed the role of radiation in the elevation of standing volume in a typical pine forest in the study area 25 years after the Chernobyl disaster.