According to the patterns of radial distribution of fiber lengthand the relationships between DBH and b-value, we consider that xylem maturation in A. mangium, A. auricuriformis and P. falcataria(Java and Solomon origins) depends on diameter growth. Formation of mature wood starts after a certain diameter is reached in these species, suggesting that we should accelerate lateral growth from the early growing stage in order to produce mature wood as early as possible. On the other hand, we consider xylem maturation is controlled by cambium age in E. globulus and E. grandis. In those species, formation of mature wood starts once a certain cambium age is attained. This suggests that lateral growth should be arrestedat an early growing stage, and lateral growth subsequently accelerated after a certain cambium age is reached, in order to reduce the percentage of juvenile wood in the harvested trunk.