[A-HW31] Surface and subsurface hydrologic models: From uncertainty analysis to water management

[AHW31-P08] Estimation of stemflow using forest inventory data and funneling ratio for Japanese cedar and Japanese cypress plantations

*Seonghun Jeong¹、Kyoichi Otsuki²、Yoshinori Shinohara³、Akio Inoue⁴、Ryuji Ichihashi⁵ (1.Graduate School of Bioresources and Bioenvironmental Sciences, Kyushu University、2.Kasuya Research Forest, Kyushu University、3.Faculty of Agriculture, University of Miyazaki、4.Faculty of Agriculture, Kindai University、5.Shiiba Research Forest, Kyushu University)

キーワード：Coniferous plantation, Diameter at breast height, Forest structure, Model, Stand density, Stand-scale funneling ratio

Even though the previous studies of stemflow (SF) had considered the portion of SF of gross rainfall (GR) minimal, the latest researches have demonstrated that the forest stand structure for specific species largely determines the stemflow ratio (SF/GR). This study develops two estimation models of SF/GR with commonly-available forest inventory data. A set of 25 SF/GRs and the forest inventory data (stand density (SD), total basal area (BA), mean diameter at breast height (DBH), and mean tree height) were collected from the previous studies of Japanese coniferous plantations (Japanese cedar and Japanese cypress). To further investigate the relation between SF/GR and forest stand structures, extra stand-structural variables (mean basal area, mean stem surface area, and total stem surface area) were derived from the inventory data, and the stand-scale funneling ratio (FR_stand) assessing the efficiency of funneling rainwater was examined. Of all the standard variables, SD solely determined the SF/GR, providing the best-fitting positive single linear regression equation as a density-based SF/GR model with a root mean square error (RMSE) of 2.4%. This model has a weak point for sustainable forest water management because the effect of tree growth over time on SF/GR cannot be reflected, but is a useful tool with the most commonly available forest inventory data for practical forest water management. On the basis of the strong correlation of the FR_stand with DBH, a size-based SF/GR model was developed with an RMSE of 2.0%. This model is adequate for sustainable forest water management because the effects of not only the SD but also tree growth on SF/GR can be reflected as the SF/GR approximately increases as a root of DBH. These models exploited from the common forest inventory data have potential implications in evaluating and controlling SF by forest water management and in developing similar models in other species and regions.