Nondestructive Evaluation of the Heartwood Color of Standing Sugi Trees by Using the Lateral Impact Vibration Method

The heartwood color of standing sugi (Cryptomeria japonica) trees was evaluated using the lateral impact vibration method. Evaluations were obtained using the diagnostic index (DFr), which is the product of the diameter D of a stem and the resonance frequency Fr obtained when the stem is laterally impacted. The heartwood color was evaluated on the basis of the following assumptions. A lower DFr implies a higher moisture content (Mc) in the heartwood, and a higher Mc implies lower brightness (L) of the heartwood color. Therefore, a low DFr might imply a low L. Seven hundred trees were measured using this method. Seventy of the 700 trees were cut to check the color of the heartwood. The increase or decrease rate R in the DFr of each tree against the regression line of D and DFr for all the cut trees was calculated as the index for evaluating L. The calculations revealed a negative correlation between R and Mc (r=0.71) and between Mc and L (r=0.70). Further, a positive correlation (r=0.53) was observed between R and L. The correlation coefficient between R and Mc was not high, but the brightness of the heartwood color (L) of the standing sugi trees could be classified into three groups by using the index R. The use of heartwood color evaluation by this method in thinning is also discussed.