Incident rainfall partitioning and canopy interception modeling for an abandoned Japanese cypress stand

Abstract

Interception loss (E_i) in forests has been studied widely. However, E_i parameters and modeling as well as spatial patterns of throughfall (TF) in abandoned Japanese cypress (Chamaecyparis obtusa) plantations remain poorly documented. In this study, gross precipitation (P_G), stemflow (SF), and TF were monitored in an unmanaged 32-year-old Japanese cypress stand throughout the 2011 rainy season. Results indicate that P_G partitioning into TF, SF, and E_i were, respectively, 64.2 ± 3.6, 10.6 ± 0.6, and 25.2 ± 1.1 % of the 880.8 mm cumulative P_G from 29 rainfall events. Direct throughfall proportion (p) and drainage from the canopy contributed about 14 ± 7 and 50 ± 21 % of the total TF for the events, respectively. The mean canopy storage capacity (S) was 2.4 ± 0.7 mm. The coefficient of variability (CV) of TF rate decreased asymptotically with increasing P_G amount, ranging from 16 to 56 % with median 26 %. The CV of TF rate was not significantly correlated with canopy cover (r = 0.152, P = 0.521, n = 20) and distance from the nearest trunk (r = 0.196, P = 0.408, n = 20). Based on the revised Gash analytical model, the total simulated E_i was close to the observed, with a general underestimation magnitude of 5.7 %. The E_i components were quantified, and most of the interception loss (62.9 %) evaporated during rainfall, while 26.8 % evaporated after rainfall ceased. Climatic and forest structural parameters required by the model were identified and analyzed by sensitivity analysis, implying that the revised Gash analytical model is robust and reliable enough for abandoned Japanese cypress plantations in a maritime climate.