Many coniferous plantations in Japan have not been managed because of the impact of economic recession on forestry. Few studies have examined rainfall partitioning (RP) in these unmanaged plantations with a stand density ≥ 2500 stems ha−1, which is a typical planting density in Japan. The aims of this study were to examine RP in an unmanaged coniferous plantation and to clarify the differences in RP with other coniferous plantations in Japan. We recorded gross rainfall (GR), throughfall (TF) and stemflow (SF) for one year in an unmanaged 32-year-old Japanese cypress (Chamaecyparis obtusa Endl.) plantation with a high stand density (2500 trees ha−1) in Fukuoka, Japan. The GR, TF and SF were 2248.6 mm, 1068.4 mm (47.5% of GR) and 425.3 mm (18.9% of GR), respectively, which resulted in interception loss (IL) of 754.9 mm (33.6% of GR). The present data were compared with the published data for all components of RP from 36 previous studies of coniferous plantations in Japan. Compared with these plantations, the present ratio of TF/GR was the lowest and the SF/GR was the highest, resulting in the highest IL/GR. This study highlights that not only TF and IL, but also SF account for a high proportion of RP in unmanaged coniferous plantations.
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