Distribution and mobilization of large woody debris in a mountain stream network, Gangwon-do, South Korea

Large woody debris (LWD) transport in headwater streams caused by forest disturbances such as wild fires, strong winds, and landslides affect the physical and ecological environment of the streams and become a disaster risk in downstream area. However, little attention has been given to LWD dynamics in South Korea where the forests comprise 63.7% of the land. As the first case study of LWD at the catchment scale in South Korea, we investigated the LWD dynamics according to the stream order in the experimental forests of Kangwon National University. The volume and number of LWD per unit channel area were 0.009 cubic m/square m and 0.04 pieces/square m in the first order stream, 0.007 cubic m/square m and 0.03 pieces/square m in the second order stream, and 0.004 cubic m/square m and 0.01 pieces/square m in the third order stream, respectively, decreasing as the order increased. The average value (+- SD) of LWD piece length/channel width ratio was 0.61 (+- 0.62) in the first order stream, 0.33 (+- 0.34) in the second order stream, and 0.16 (+- 0.14) in the third order stream. The correlation between mid-diameter and length for coniferous and natural wood pieces was relatively high in the first order stream, but low in the second and third order streams, indicating downstream fragmentation. For the decay classes of LWD, class I to III gradually decreased, whereas class IV greatly increased as the stream order increased. LWD mobility was 60% for the first order stream, 56% for the second order stream, and 86% for the third order stream. Traveled distance of LWD was inversely related to the piece length/channel width ratio and increased more in the high order streams than in the low order streams. These results contribute to understanding the volume, distribution and mobilization of LWD within a stream network in Korean mountain catchments.