Variation of Wood Properties with Height Position in the Stems of Obi-Sugi Cultivars

To promote the use of sugi woods, the information on the variation of wood properties is very important. Obisugi is a major group of sugi cultivars planted in Southern Kyushu. However there is no information on the variation of wood properties with height position in the stems of Obi-sugi trees. We examined in detail the difference between the wood properties at 5 m above ground (upper height position) and those at 1.5 m above ground (lower height position) of Obi-sugi cultivars. Obtained results were as follows : Mechanical properties in both mature and juvenile wood at the upper height position were higher than those at the lower height position in most cultivars. Radial variations of mechanical properties at the upper height position were larger than those at the lower height position in most cultivars. Microfibril angle of latewood tracheids (MFA) in both mature and juvenile wood at the upper height position was smaller than those at the lower height position in most cultivars. On the other hand, basic density and latewood tracheid length in both mature and juvenile wood at the upper height position did not differ from those at the lower height position in many cultivars. Higher mechanical properties at the upper height position were mainly the result of the decrease of MFA with height position. In addition, to examine the whole tree variation from top to bottom, we investigated the variation of wood properties of Obi-sugi trees at different height increments. The results suggested that longitudinal variations of mechanical properties were well explained by variations of MFA and basic density, and that height increment affected the mechanical properties and the longitudinal variation pattern of wood properties.