Change of interception process due to the succession from Japanese red pine to evergreen oak

Extensive measurements of rainfall, throughfall and stemflow in a forest during succession from Japanese red pine (Pinus densiflora Sieb. et Zucc.) to a combination of red pine and lower canopy trees—evergreen oak (Quercus myrsinaefolia Blume) and evergreen theaceous tree (Eurya japonica Thunb.) allowed the effect of this succession on the interception of rainfall to be evaluated. The measurements were conducted on two occasions: 1984/1985, and 2001/2002 when the lower canopy trees had become dominant. During this period, 75% of the red pines had been removed, and there was a substantial increase in stemflow (p<0.01), essentially no change in throughfall (p<0.01), and a substantial decrease in interception (p<0.01). The increase in stemflow was attributed to the increase in lower canopy trees; trees that have steeply angled branches, smooth bark surfaces and water repellent leaves; all of which enhance stemflow. The decrease in interception was due to the decrease in canopy water storage (2.6–1.1 mm/event) and an increase in evaporation during rainfall event (0.7–1.1 mm/event). The decrease in storage partly resulted from the removal of red pines, the bark of which is thick, flaky, and therefore, very absorptive. It was responsible for 88% of the actual rainfall storage at the beginning of the experiment. During the 17 year-period, the size of the lower canopy trees increased more rapidly than that of red pines. The increase in evaporation was due to the increase in canopy gaps by the removal of 75% of the red pines during the succession, and was a minor factor in affecting interception loss.