Juvenile Wood of Hardwoods Judged by Density Variation

In the ring-porous hardwoods the changes of basic density are influenced by ring width, while basic density of diffuse-porous hardwoods is almost independent of ring width. The radial variations of basic density in each ring width class are useful for distinguishing between age and growth effects. In three species of ring-porous hardwoods and four of diffuse-porous hardwoods grown in Hokkaido, Japan, these effects were investigated. The age effects on density were quite clear in all hardwoods, so juvenile wood could be defined as the region around the pith without growth effects on density and showing a decrease or increase in density outward. The growth effects on density were significant in mature wood of all ring-porous hardwoods and in the diffuse-porous Katsura (Cercidiphyllum japonicum), while in the other diffuse- porous hardwoods there was no growth effect on density. The change of basic density was also affected by the height level in the tree. Age and growth effects should be considered separately for lower, medium and upper height levels in the tree. Anatomical features were studied in some hardwoods in relation to age, growth and height effects on density variation. Age effects on density are due to the proportion of late wood in oak, to differences in vessel frequency and diameter in Katsura, and to relative fibre wall thickness in birch.