Growth and wood properties of rapid-grown Japanese Larch.

Japanese larch grown under intensive management practices (i.e. fertilization, irrigation, and cultivation) exhibited rapid juvenile growth; diameter and height averaged 15.7 cm and 9.2 m, respectively, in 10 yr. Whole-ring specific gravity decreased for several years after fertilization and then increased; it was influenced by the presence of large amounts of transition wood and low latewood percent. X-ray analysis also showed that specific gravity was quite uniform within the annual rings after fertilization. The percentage of extractives was low throughout the trees; this may have been related to the absence of heartwood formation. The pattern of both latewood percent and percent of extractives indicated that the juvenile wood zone in these trees was 10 yr. Furthermore, compression wood was present in most annual rings although it was primarily associated with the latewood. The possibilities of selecting for growth and wood properties in a tree improvement program for Japanese larch are discussed.