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Migration of Radiocaesium with Litterfall in Hardwood-Japanese Red Pine Mixed Forest and Sugi Plantation. J Jpn For Soc 95: 267 274 To clarify radiocaesium migration with litterfall from the tree canopy to the forest floor, a study was conducted in the three different forests in Fukushima Prefecture where radionuclides released from the Fukushima Daiichi Nuclear Power Plant FDNPP were deposited. Concentrations of 134 Cs and 137 Cs in the litterfall had been periodically monitored for 11 months since four months after the accident and were analyzed. The concentrations in the litter samples were generally higher in the cedar forests than those in the hardwood-Japanese red pine mixed forest; because the hardwood trees had no leaves at the time of the accident, most of the resuspended radiocaesium is considered to have been deposited on the forest floor through canopies. Meanwhile, the cumulative deposition of radiocaesium in the cedar forests was found to be higher than that in the hardwood-Japanese red pine mixed forest. This confirmed that large amount of radiocaesium still remains in the tree canopies. Although not many differences were observed in the radiocaesium concentrations in the litterfall since October 2011 in any forest stand, radiocaesium deposition remarkably increased due to a large amount of litterfall from the canopies. Together with the litterfall, vertical distribution of fresh leaves in the canopies, horizontal distribution of litter on the forest floor, throughfall, and stemflow should be monitored to clarify the comprehensive migration of radiocaesium in the future.

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Long-term monitoring revealed that radiocesium ( 137 Cs) deposition that fall from the canopy with litterfall was characterized by forest types, seasonal change, and canopy closure (CC). The sum of autumn and spring 137 Cs deposition values divided by the sum of summer and winter tended to have higher values in the cedar forest. The angle of view α when the correlation between the CC size and litterfall amount is strongest, was 5° or less in the young cedar forest, but varied in the hardwoodpine mixed forest. This indicates the spatial distribution of 137 Cs deposition has heterogeneity and homogeneity in each forest.