Relations of fiber length to within-tree variation of ultrasonic wave velocity in fast-growing trees

The within-tree variation of longitudinal wave velocities in Acacia auriculiformis (AA), Eucalyptus dunnii (ED), and Melia azedarach (MA) was experimentally investigated. The velocities in the longitudinal direction (V_L) exhibited a minimum value near the pith. The minimum values in AA, ED, and MA were measured to be 4000, 4600 and 3600 m/s, respectively. V_L increased from the pith to the bark. On the other hand, the velocities in the radial and tangential directions exhibited constant values. The radial variation patterns of the V_L coincided with those of fiber length (FL). V_L exhibited a strong correlation with the FL at a 1% significant level. These findings revealed that wood properties such as FL greatly influence the velocity in the longitudinal direction.