After Quercus serrata die-off following Japanese oak wilt disease (JOW), the remaining vegetation could show higher transpiration (T_r) caused by the greater availability of solar radiation, soil water, and nutrients. Since plant T_r plays a key role in the hydrological cycle, understanding the T_r response of neighboring trees is important for accurate evapotranspiration (ET) estimation in JOW infested catchments. In this study, girdling treatment was applied to three canopy layer Q. serrata trees (treatment groups) in a secondary forest site to simulate JOW effect on neighboring trees. Before and after applying the treatment whole-tree sap flux densities (F_d ) of neighboring trees in the treatment groups and one control group were measured using Granier sensors for one growing season. A linear mixed model was employed to compare F_d of trees in the treated groups with that of control. Results showed that F_d in neighboring trees did not increase significantly following the treatment (p>0.05), indicating there was no significant T_r increases in neighboring trees to compensate for the T_r loss by Q. serrata die-off. Therefore, ET reduction in JOW infested watersheds was predicted.