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We determined the axial and radial xylem tension gradients in trunks of young Douglas-fir ( Pseudotsuga menziesii  (Mirb.) Franco) trees. Axial specific conductivity ( k  s-a ) and sap flux density ( J  s ) were measured at four consecutive depths within the sapwood at a stem height of 1 m. By definition, at a given position in the bole,  J  s  is a function not only of  k  s-a  but also of the driving force for water movement. The  J  s : k  s-a  ratio was therefore used to estimate axial tension gradients and the radial gradients at a stem height of 1 m were calculated from the differences in axial tension gradients at each depth. Tracheid lumen diameter and tracheid length were used to predict differences in  k  s-a  and its divergence from the theoretical  k  s-a  determined by the Hagen Poisseuille equation. The ratio of  k  s-a  (determined in the laboratory) to  J  s  (measured in the field) varied with depth in the sapwood, resulting in non-uniform axial and radial tension gradients from inner to outer sapwood. Transpiration-induced axial tension gradients were in the range of 0.006−0.01 MPa m −1  excluding the gravitational tension gradient. At a stem height of 1 m, radial tension gradients were in the range of 0.15–0.25 MPa m −1  and were lower in the middle sapwood than in the inner or outer sapwood. Axial tension gradients were 44–50% higher in the outer sapwood than in the inner sapwood. At a stem height of 1 m, radial  J  s , calculated on the basis of radial tension gradients and measured radial specific conductivity ( k  s-r ), was about two orders of magnitude smaller than axial  J  s . Our findings indicate that large radial tension gradients occur in the sapwood and clarify the role played by xylem  k  s-a  and  k  s-r  in determining in situ partitioning of  J  s  in the axial and radial directions.

Transpiration-induced axial and radial tension gradients in trunks of Douglas-fir trees