As a diagnostic method of the butt heart rot in living Chamaecyparis obtusa trees, the lateral impact vibration method that is a simple and non-destructive diagnosis was examined. The index of the diagnosis is the product (D×Fr value) of the resonance frequency (Fr) by lateral impact and the diameter (D) of a tree. D×Fr value of 1481 trees in 16 stands was measured, and the values varied extensively within 13 to 46 cmkHz. In order to show the range of D × Fr values of healthy trees, we cut down 121 trees and investigated on their wood qualities. As a result, the values of 99 healthy trees were distributed within 30 to 42 cmkHz, with the difference among stands or individuals. The relation between the occurrence of hollow or rot and the D × Fr value was examined, using the disks taken from healthy trees or damaged trees. As the hollow or rot area became larger, the D×Fr value decreased. This method could detect the hollow and rot on the disks sensitively.
Stress-wave velocity at the base of trunk in the transverse direction was investigated in 160-year-old and 115-year-old Larix kaempferi stands in the Asamayama National Forest. The mode of frequency distribution of stress-wave velocity classes of both 160-year-old and 115-year-old stands was 1.8 km s-1. Both stands exhibited a J-shaped frequency distribution which is typical of stands including butt-heart-rot trees. Assuming that stress-wave velocity classes below 1.4 km s-1 indicated total decay based on previous reports, we estimated that 24 percent of the total individuals were decayed in 115-year-old stand and 25 percent in 160-year-old stand. Fruitbodies of Cryptoderma pini were observed on the base of dead branches of 160-year-old Larix kaempferi trees. We surmised that stem-heart-rot is occurring in addition to butt rot in the 160-year-old stand. When stem rot is included, thirty-six percent of total individuals would be considered decayed in the 160-year-old stand.