It is difficult to scale up measurements of the sap flux density(J_S) for the characterization of tree or stand transpiration(E) due to spatial variations in J_S and their temporal changes.To assess spatial variations in the sap flux density of Korean pine(Pinus koraiensis) and their effects on E estimates,we measured the J_S using Granier-type sensors.Within trees,the J_S decreased exponentially with the radial depth,and the J_S of the east aspects were higher than those of the west aspects.Among trees,there was a positive relationship between J_S and the tree diameter at breast height,and this positive relationship became stronger as the transpiration demand increased.The spatial variations that caused large errors in E estimates(i.e.,up to 110.8 % when radial variation was ignored) had varied systematically with environmental factors systematic characteristics in relation to environmental factors.However,changes in these variations did not generate substantial errors in the E estimates.For our study periods,the differences in the daily E(E_D) calculated by ignoring radial,azimuthal and tree-to-tree variations and the measured E_D were fairly constant,especially when the daily vapor pressure deficit(D_D)was higher than 0.6 k Pa.These results imply that the effect of spatial variations changes on sap flow can be a minor source of error compared with spatial variations(radial,azimuthal and tree-to-tree variations) when considering E estimates. It is difficult to scale up measurements of the sap flux density (J_S) for the characterization of tree or stand transpiration (E) due to spatial variations in J_S and their temporal changes. To assess spatial variations in the sap flux density of Korean pine ( Pinus koraiensis) and their effects on E estimates, we measured the J_S using Granier-type sensors. Trees in the trees, the J-decreased exponentially with the radial depth, and the J_S of the east aspects were higher than those of the west aspects. Among trees , there was a positive relationship between J_S and the tree diameter at breast height, and this positive relationship became stronger as the transpiration demand increased.The spatial variations that caused large errors in E estimates (ie, up to 110.8% when radial variation was ignored ) had varied systematically with environmental factors systematic characteristics in relation to environmental factors. However, changes in these variations did not generate substantial errors in the E estimations tes.For our study periods, the differences in the daily E (E_D) calculated by ignoring radial, azimuthal and tree-to-tree variations and the measured E_D were fairly constant, especially when the daily vapor pressure deficit (D_D) was higher than 0.6 k Pa. These results imply that the effect of spatial variations changes on sap flow can be a minor source of error compared with spatial variations (radial, azimuthal and tree-to-tree variations) when considering E estimates.