Hydro-Sedimentological Dynamics of Rainfall Interception and Soil Erosion Across Canopy Elevation Gradient

This study investigates how canopy elevation regulates throughfall, rainfall interception, and soil erosion, testing whether trees of the same species but with different crown heights are low, medium, high exert distinct hydrological and sedimentological effects under natural rainfall.

A year-long field experiment was conducted in woodland at Ritsumeikan University. Gross rainfall was recorded by a rain gauge installed in a nearby open area. Under each of three canopy elevation classes, three experimental soil boxes 37 cm × 25 cm were installed on a 20° slope and subdivided into compartments filled with decomposed granite and silica sand. Nineteen rainfall events were monitored in total. From Event 10 through Event 19, one rain gauge and three bottle collectors were deployed beneath each canopy class to measure throughfall. Soil displacement was measured within a designated 6 cm × 15 cm reference area in each box. This design enabled quantification of gross rainfall, throughfall partitioning, interception losses, and soil detachment across canopy elevations.

Throughfall ratios showed clear elevation dependence: high canopies transmitted the largest proportion of gross rainfall, whereas low canopies retained more water and produced less throughfall. Correspondingly, soil erosion rates were highest beneath high canopies and lowest beneath low canopies. Across all canopy classes, decomposed granite produced greater erosion than silica sand, consistent with its finer texture, lower cohesion, and higher susceptibility to raindrop impact. Conclusion Canopy elevation strongly modulated rainfall redistribution and erosive energy. High canopies enhanced throughfall and sediment yield, while low canopies buffered rainfall energy and reduced soil loss. These results highlight canopy structural variation as a key control on forest hydrology and sediment dynamics, with implications for erosion management and sustainable woodland design.