The relations of fiber length, wood density, and compressive strength to ultrasonic wave velocity within stem of Melia azedarach

Radial and axial variations in the longitudinal ultrasonic wave velocity within stem of 17–19-year-old Melia azedarach planted in two different sites in northern Vietnam were experimentally investigated. Wood samples were collected from 10, 50, and 90% of the radial length from pith at 0.3, 1.3, 3.3, 5.3, and 7.3 m heights above the ground to measure ultrasonic velocity (V_u), fiber length (FL), air-dry density (AD), and compressive strength (CS) at moisture content approximately 12%. The average wave velocity for two sites exhibited minimum value near the pith about 3700 m/s. It kept increasing to 4200 m/s at the middle position before remaining constant value forward to outside. In axial direction, the variation of V_u with height was very small and without statistical significance. V_u had a strong positive linear relationship with both FL (r = 0.69, p < 0.001) and AD (r = 0.67, p < 0.001). These findings reveal that the FL and AD greatly influence the within-tree variations in the ultrasonic wave velocity in M. azedarach. Besides, the significant positive linear correlation between CS and V_u suggests that V_u was a useful predictor of the CS for M. azedarach planted in northern Vietnam.