Application of Three Canopy Interception Models in a Japanese Cedar (Cryptomeria japonica D. Don) Forest Before and After Intensive Thinning

Abstract:

Recently, forest management practices, such as thinning and pruning, were infrequently conducted in coniferous plantations of Japan. Some researchers in Japan have speculated that unthinned plantations could consume more water via evapotranspiration from the dense canopies and cause a loss of water resources. Therefore, some prefectures in Japan conducted intensive thinning of coniferous plantations, mainly to secure water resources. Although canopy interception loss (I_c) is a major component of evapotranspiration, few studies have examined changes in I_c due to intensive thinning. We measured I_c in a Japanese cedar (Cryptomeria japonica) forest, the most common type of plantation in Japan. We compared and contrasted three canopy interception models (Mulder, revised Gash, WiMo) before and after intensive thinning operations. The experimental Japanese cedar forest was intensively thinned with removal of 54% of all stems, reducing the stocking level from 1300 to 600 stems ha^-1 and the basal area by 50% from 99.7 to 49.6 m² ha^-1. The ratios of throughfall (T_f), stemflow (S_f), and I_c to precipitation (P_r) (i.e., T_f/P_r, S_f /P_r, and I_c/P_r) before thinning were 74%, 12%, and 14%, respectively. After thinning, those percentages changed to 86%, 6%, and 8%, respectively. Thus, thinning decreased I_c by 43%, a value comparable to changes in stem density and basal area. The Mulder model represented the measured I_c well, both before and after thinning. I_c for the revised Gash and WiMo models tended to be larger than the measured I_c both before and after thinning. This suggests that the Mulder model might be best suited to predict canopy interception losses from Japanese cedar plantations before and after thinning operations.