We report on the behavior of radiocesium in tree bark and its transfer into the stemflows of chestnut trees in a forest in the Fukushima Prefecture, Japan. In stems that were present at the time of the accident, the radiocesium concentration of the bark was found to be approximately 10 times that of the wood. The average Cs-137 concentration of the dissolved fraction (<0.45 mu m) in the stemflow was measured to be around 10 Bq/L. The Cs-137 concentration ratio [present at the time of the accident (Bq/kg) in the bark/the dissolved fraction in the stemflow (Bq/L)] was approximately 10(3). A strong positive correlation was observed between the radiocesium concentration and the electrical conductivity of the dissolved fraction of the stemflow; this result suggests that radiocesium and electrolytes have the same elution mechanism from the tree. The size fractionation analysis of the <0.45 mu m fraction through ultrafiltration revealed that the radiocesium was present as an almost dissolved species. Some of the particles in the particulate fraction (>0.45 mu m) of the stemflow were strongly adsorbed radiocesium. (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.