The research on the relationship between stand structures and rainfall partitioning (RP) of gross rainfall (GR) into throughfall (TF), stemflow (SF), and interception loss (IL) was conducted in the two dense unmanaged Japanese cypress plots at an age of 33 years with stand density of 2500 stems ha-1, and the results were compared with the previous studies. The results showed that (1) TF/GR significantly decreased, but SF/GR and IL/GR significantly increased with increasing stand density, which confirms that stand density is an informative stand structure factor for all the RP components in coniferous plantations. In addition to stand density, canopy cover ratio and storage capacity could also be influential stand structure factors for RP. (2) Having the highest stand density, TF/GR were the lowest class and SF/GR and IL/GR were the highest class in the two study plots. In detail, however, the plot with smaller stand with denser and thicker dead branch layers had the exceptionally low TF/GR compared with the other plot, but SF/GR in both plots were almost identical. (3) TF/GR decreased with increasing number of dead branches possibly because of increasing rainwater interception by dead branches, while it increased with increasing vertical dead branch space possibly because of increasing rainwater splash by dead branches. SF/GR could increase by dead branches possibly because of the additional gain of rainwater by the dead branches. However, the number of dead branches did not affect SF/GR possibly because the dead branches generating SF could be limited to the upper dead branches. These findings will contribute new information to the studies on RP in coniferous plantations and guide better silvicultural practices for effective forest ecological services.
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