Effects of radial growth rate on selected indices for juvenile and mature wood of the Japanese larch

To examine the differences between juvenile and mature wood, 12 aged sample trees from two areas of Nagano Prefecture were harvested; and the radial d evelopment of tracheid length, the ring density, and the relation of the ra dial growth rate (observed by ring width) with some selected indices of rin g structure were investigated. The results proved that the radial variation of tracheid length with ring number can be described by a logarithmic form ula, and both plantations reached the demarcation of juvenile and mature wo od at age 18. With the segmented regression method, we also analyzed radial variation of mean density and found that the demarcation of juvenile and m ature wood was at age 15 for sample trees from Saku and at age 21 for those from Yabuhara. By using the results of estimates from juvenile and mature wood based on ring density, we found that high growth rates resulted when p roducing lower-density wood during the juvenile period, but these rates did not occur during the mature period. The basic reason for this phenomenon i s the variation in patterns of earlywood and latewood in juvenile and matur e wood, respectively. This result advised us that when managing plantations of Japanese larch it is necessary to take different measurements at differ ent growth periods.