Heartwood moisture content of standing Japanese cedars was studied by lateral impact vibration method. It is possible to estimate wood qualities and heartwood moisture content of tree trunk by the non-destructive and easy method. The obtained results are summarized as follows : 1) No seriously defected tree which has cavity or decay was found in this study from analysis of the relation between tree trunk diameter and inverse of lateral impact frequency. 2) Equivalent heartwood moisture contents of the cultivars “Measa”, “Yabukuguri”; and “Aya”, which were estimated by the lateral impact method, were almost the same as the values obtained by kiln-dried method. 3) From the equivalent moisture contents of heartwood at the height of 0.3 and 1.2 m, it was possible to roughly group the tested cedar cultivars into two, the three cultivars of high correlation and the other four of low correlation.

Development of butt rot were investigated in the trunks of 25-, 35-, and 50-year-old hinoki cypress stands. The decayed parts in the trunks of the 25-, 35-, and 50-year-old trees were 1.0-26.0 cm (average 7.0 cm), 1.5-26.0 cm (average 14.1 cm), 2.5-35.5 cm (average 14.0 cm) in diameter at the cut surface, and reached the height of 10-180 cm (average 66.2 cm), 20.0-300.0 cm (average 139.5 cm), and 30.0-430.0 cm (average 199.8 cm) from the cut surface, respectively. The older the trees, the higher the decay developed. The influence of butt-rot on yield volume was estimated in the 35 -year-old stand. The volume of the rotten part was 0.9169 m³, which was only 6.95% of the expected yield volume. However, the volume of logs that were cut off and left in the forests was 4.1569 m³, so the total loss was reached 31.5% of the expected yield.