Following the Chernobyl accident, the scientific community gained
numerous data on the transfer of radiocesium in European forest
ecosystems, including information regarding the short-term
redistribution of atmospheric fallout onto forest canopies. In the
course of international programs, the French Institute for Radiological
Protection and Nuclear Safety (IRSN) developed a forest model, named
TREE4 (Transfer of Radionuclides and External Exposure in FORest
systems), 15 years ago. Recently published papers on a Japanese
evergreen coniferous forest contaminated by Fukushima radiocesium
fallout provide interesting and quantitative data on radioactive mass
fluxes measured within the forest in the months following the accident.
The present study determined whether the approach adopted in the TREE4
model provides satisfactory results for Japanese forests or whether it
requires adjustments. This study focused on the interception of airborne
radiocesium by forest canopy, and the subsequent transfer to the forest
floor through processes such as litterfall, throughfall, and stemflow,
in the months following the accident. We demonstrated that TREE4 quite
satisfactorily predicted the interception fraction (20%) and the
canopy-to-soil transfer (70% of the total deposit in 5 months) in the
Tochigi forest. This dynamics was similar to that observed in the
Höglwald spruce forest. However, the unexpectedly high contribution of
litterfall (31% in 5 months) in the Tochigi forest could not be
reproduced in our simulations (2.5%). Possible reasons for this
discrepancy are discussed; and sensitivity of the results to uncertainty
in deposition conditions was analyzed.