Changes in Radioactive Cesium Distribution in Forests
Regarding radioactive cesium in the surveyed forests, in the first one year after the accident from 2011 to 2012, the percentage of radioactive cesium found in leaves, branches and litter layers decreased significantly, while that found in soil increased significantly. This is considered to be because radioactive cesium deposited on leaves and branches, etc. of trees gradually transferred to the litter layer on the ground due to rain or leaf fall and then transferred to soil due to the decomposition of the litter layer. The percentage of radioactive cesium in soil is continuously increasing, and over 90% of the radioactive cesium in forests is found in soil or the litter layer as of FY 2023, mostly found in the soil surface layer at a depth between 0 cm and 5 cm.
The concentration of radioactive cesium found in leaves, branches, and tree bark has been decreasing as a whole since the commencement of the survey in FY2011. The concentration in litter layers decreased by 90% or more at all locations from FY2011 to FY2023. Regarding soil, the concentration is the highest in surface soil (the layer at a depth between 0 cm and 5 cm), but changes in the concentrations vary by area and no clear tendency is observed.
Meanwhile, cumulative doses of radioactive cesium in forests as a whole have not shown any clear changes. According to surveys and other data on the Chornobyl Nuclear Power Station Accident, it is thought that radioactive cesium stays in forestry ecosystems and that part of such radioactive cesium circulates internally. Cumulative doses in forests as a whole change only little over years and radioactive cesium is generally accumulated near the soil surface. Accordingly, it is considered that the amount of radioactive cesium that flows out of forests is small. Furthermore, it has become clear that changes in the concentrations of radioactive cesium in wood are minor even after the lapse of time since the accident and that trees absorb radioactive cesium from soil through their roots.
(Related to p.186 of Vol. 1, “Distribution of Radioactive Materials in Forests”)
- Included in this reference material on January 18, 2016
- Updated on March 31, 2025