Plot-scale study of surface runoff on well-covered forest floors under different canopy species

To investigate the effects of vegetation canopy on surface runoff, four runoff plots (2 m × 1 m in size) were established under different types of forest canopies (S1: sawtooth oak and Japanese larch; S2: Chinese cork oak; S3: shrub; and S4: Korean pine) on a mountain slope in central Korea. Rainfall, throughfall, and surface runoff were measured from July 2007 to October 2009. During the observation period, there was no storm event with a rainfall intensity that exceeded the average value for infiltration rates at the runoff plots. Each plot showed differences in surface runoff generation (S1 > S2 ≒ S3 > S4). The plots with broad-leaf litter layers had higher maximum water storage capacities than the plot with a needle-leaf litter layer. These results imply that the water storage capacity and the leaf shape of the litter layer affected surface runoff generation. Moreover, under dry conditions (<20 mm of API7), the rainfall threshold for all plots, except S4, required for surface runoff generation decreased and surface runoff from all plots increased slightly compared with relatively wet conditions (>20 mm of API7). Storm runoff coefficients at all plots decreased drastically as the value of API7 increased. This suggests that the lowering of the rainfall threshold for surface runoff generation and the resulting increase in surface runoff might be related to the development of hydrophobic conditions on the soil surface caused by dry conditions. Therefore, in addition to leaf shape and water storage capacity of the litter layer, the soil water condition also can be an important factor in plot-scale evaluations of surface runoff generation from a slope well covered with litter layer.