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 2021, mostly found in the soil surface layer at a depth between 0 cm and 5 cm.

The percentage of radioactive cesium found in the litter layer is high in the Kaneyama cedar forest and is low in other forests. Each forest thus shows different tendencies. The survey will be continued into the future.
(Related to p.184 of Vol. 1, “Distribution of Radioactive Materials in Forests”)

• Included in this reference material on January 18, 2016
• Updated on March 31, 2023