This review summarizes recent studies on the diurnal periodicity in wood cell wall formation, with a major focus on those that we have conducted. Differences in the innermost surface of developing secondary walls of differentiating conifer tracheids can be seen from day to night. Cellulose microfibrils are clearly evident during the day, and amorphous material containing abundant hemicelluloses is prevalent at night. These findings suggest a diurnal periodicity in the supply of cell wall components to the innermost surface of developing secondary walls during tracheid cell wall formation in conifers. Further studies have demonstrated that these diurnal differences correspond to the 24-h light-dark cycle and diurnal changes in the volume of differentiating cells. This diurnal periodicity is likely associated with diurnal changes in light conditions and the water status, such as the turgor pressure, of differentiating cells.

View full abstract

To evaluate dimensional changes and twists after the molding process of air-seasoned timber, air-seasoning tests were conducted on Japanese red pine (Pinus densiflora Sieb. et Zucc.) rectangular timber which is chiefly used for beams and girders of Japanese conventional wooden houses. Six air-seasoning periods were tested: 160, 260, 400, 520, 890, and 1250 days. Occurrences of dimensional changes and twists of timber that was kiln-dried after various air-seasoning periods were also evaluated for comparison. Dimensional changes and twists after molding of timber were relatively small when the moisture content (MC) was low, and MC of timber with an air-seasoning period over 260 days was lower than the MC of other timber air-seasoned for 160-days. We recommend that the stabilities of MC, dimensional changes, and twists should be almost reached over 260-days air-seasoning. The dimensional changes of timber air-seasoned over 260 days were 1.5mm or less, so it was suggested that air-seasoned timber meets the specification of the Japanese agricultural standard for structural lumber. It was also clear that additional kiln-drying was effective to reduce dimensional changes and twists.

View full abstract

The strength distribution of laminated veneer lumber (LVL) has not been estimated by Mont Carlo simulation, because it is very difficult to characterize the elements of LVL. In this report, we tried to estimate the strength distributions of the elements by a nonlinear least-squares method, supposing the element as a veneer with adhesive and using the strength data of LVL composed of a single veneer. In addition, the suitability of parameters of the strength distribution of elements, calculated as the converged solutions, were confirmed by the results of simulation for LVL strength distributions using those parameters and were verified by K-S test. The suitable statistical distributions could be estimated in the strength of the elements, modulus of elasticity in the horizontal and vertical use direction, tensile strength and compression strength, among normal distribution, lognormal distribution and 2P-Weibull distribution. In bending strength of the elements in the horizontal use direction, the most suitable criteria of LVL bending strength and the suitable statistical distributions under this criteria could be estimated.

View full abstract

Within-tree variation (at the positions of 0.2, 2.2, 4.2, and 6.2m above the ground) of wood properties was investigated in the 59-year-old kuromatsu (Pinus thunbergii) No.26F₁ family, an open-pollinated family of kuromatsu No.26 selected by growth characteristics in the tree breeding program. Trees of akamatsu (P.densiflora) of the same age were used for comparing wood properties. No significant differences in basic density (BD) and latewood tracheid length (TL) at 4 different heights, except for BD at 6.2m, were recognized between kuromatsu No.26F₁ and akamatsu. In addition, significant differences between kuromatsu No.26F₁ and akamatsu were not found in microfibril angle of the S₂ layer in latewood tracheids (MFA), modulus of elasticity and modulus of rupture in static bending, and compressive strength parallel to grain at 2.2m height. On the other hand, the boundary between juvenile wood (JW) and mature wood (MW), which was determined by TL and MFA, was within the 15th to the 20th annual ring from the pith in both kuromatsu No.26F₁ and akamatsu. In addition, significant differences in mean values of wood properties in JW and MW were not found between kuromatsu No. 26F₁ and akamatsu, except for BD of MW at 6.2m

View full abstract

No strength data existed for keyaki (Zelkova serrata) full-sized timber because the keyaki used had dimensions of around 180×180mm or more, even in common houses. Due to the lack of full-sized strength data, the validity of the design strength requirement value of keyaki as full-sized timber was unclear. Moreover, no fundamental data existed to determine the grading method, because the effect of timber quality and defects such as knots on the strength properties also remained unclear. In this study, bending and compressive tests were conducted using full-sized keyaki timber, and these problems were examined. Strength tests using small clear specimens of keyaki were also conducted and compared with the results for full-sized timber and the design strength requirement value. As a result of bending tests using full-sized timber, it was found that the visual grading method and the machine grading method could be applied to keyaki timber as well as to coniferous timber. However, additional study is needed on the effect of grain angle. Based on the results of bending and compressive tests using full-sized timber and strength tests using small clear specimens, it was found that the design strength requirement value of keyaki now in use is reasonable.

View full abstract

We calculated the Carbon Footprint of Products (CFP) of lumber locally produced for local consumption and manufactured by six types of sawmills. First, we calculated and compared CFPs of lumber with and without the kiln-drying process, and we obtained the average of CFP for lumber certified by Kyoto prefecture. Then, we studied the effect of differences in the process on CFPs based on the calculated results. Accordingly, “The rate of kiln-dried lumber”, “The heat source of the kiln-drying process” and “Transport processes of logs and of lumber products” respectively made impacts on CFP for lumber certified by Kyoto prefecture, and countermeasures for reducing CFP differed depending on the scale and/or manufacturing process of sawmills.

View full abstract