Abstract
To elucidate the source area of leaf litter in streams, we investigated the travel distance of leaf litter from willow (Salix spp.) trees at two flat riparian forests in Hokkaido (in Akagawa and Yufutsu). We marked the willow leaves by spray-painting them to an aboveground height of 13.5 m using an aerial work platform, and we surveyed their dispersal with litter traps. Leaves of the upper crown were found to disperse within 15-25 m from the base of the trunks, whereas leaves of the lower crown were found to disperse within only 5-15 m because the heights from which they fell were relatively low. Directional differences in dispersal area were related to wind direction during the leaf fall season, and there were positive correlations between maximum dispersal distances and wind intensities. Leaf litter redistribution on the forest floor was surveyed using artificial leaves from late fall until late spring. The average travel distances of the leaves were very short (0.04-2.15 m), and the travel directions relate to the directions of strong winds (≥5 m/s or ≥6 m/s) near the floors. Leaf litter travel distance at flat riparian forests in snowy region is considered to depend more on leaf dispersal during leaf fall than on redistribution on the floor.
