The effect of competitive neighboring trees on diameter growth of a focal tree was examined to provide an indicator for individual tree management in 44- to 91-year-old Japanese cedar and Hinoki cypress plantations in Shikoku, Japan. Mean growth rate of tree diameter at breast height (DBH) ranged from 0.30 to 0.39 cm yr^-1. The DBH size at the beginning of the census period did not sufficiently account for the variation of DBH growth in Hinoki cypress stands compared to that in Japanese cedar stands. We employed competition indices based on sum of basal areas of neighboring trees within varying distances from a focal tree. The improvement of linear statistical model for prediction of tree diameter growth by adding competition indices as an explanation variable varied with the type of competition indices. In the 44- to 50-year-old overcrowded stands, one-sided competition, in which the growth of the focal tree was influenced only by larger neighboring trees, was prominent. However, in the 65- to 75-year-old stands, two-sided competition, in which the growth of the focal tree was influenced by all neighboring trees, had significant effects. These results suggest that tree positioning, paying attention to neighborhood competition, is crucial in management of old-aged plantations.

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We investigated the effects of tree thinning on stand structure dynamics and diameter growth in two old and overcrowded Japanese cypress (Chamaecyparis obtusa) stands over an 8-year period after thinning. One stand was subjected to canopy thinning and the other to suppressed tree thinning. The density of high-quality trees was 300 trees ha^-1 in both stands after thinning, but in the stand that had been thinned of canopy trees the density of low-quality trees was still high. Height-to-diameter ratio decreased in the stand subjected to thinning of suppressed trees, whereas it increased in the stand subjected to canopy tree thinning. The annual relative diameter growth rate after thinning ranged from 0.70% year^-1 to 1.17% year^-1 and was 0.2% to 0.5% better than that before thinning. There are therefore cases in which thinning increases diameter growth, even in old and overcrowded stands.

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Mature Sugi (Cryptomeria japonica) plantations that have been managed for over 50 years have increased in number throughout Japan. However, there are no criteria or indicators for tree selection before thinning. Here, we attempted to expand the understanding of sunny crown management in Yoshino Forestry by analyzing a mature artificial Sugi stand at Sanbe Educational and Research Forest, Shimane University. We examined the correlation of sunny crown diameter and annual diameter at breast height (DBH) growth, and the accuracy of annual ring growth estimates. We found a correlation between sunny crown diameter and annual DBH growth; with 79% accuracy, were able to estimate whether the annual ring width was 2 mm using sunny crown diameter ranges. Therefore, although sunny crown and DBH size is associated with different numbers of thinning times, it is a useful indicator of tree selection for thinning in the Sanbe mature forest, and may also be a useful indicator in thick, mature Sugi plantation forests in Japan.

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We examined current trends in harvesting methods in Japan's aging plantation forests with respect to forest road networks and the limitations on extraction imposed by terrain. On moderate terrain there is potential for a transition from the use of conventional swing yarders towards recently developed European tower yarders, which are sufficiently powerful to enable the extraction of large trees over greater distances. We considered an example from the Kami area in the Kochi Prefecture and found that the adoption of such a system required a significant upgrading of the forest road network. An alternative approach, applicable to working on steeper terrain, is the use of a dense network of narrow forest roads, which demands the use of smaller machines with correspondingly limited extraction distance. We found numerous examples of this approach in western Japan and Shikoku Island. For both approaches discussed, finding the right balance between investment in harvesting system technologies and forest profitability is key. Our analysis suggests that a transition to the use of tower yarder systems can reduce total harvesting costs and that there are opportunities to make further efficiencies. These include the domestic production of tower yarders, intensification of forest management to increase production of high quality timber, and greater reliance on in-house rather than outsourced labor.

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Since the ratio of Sugi (Cryptomeria japonica D. Don) large diameter logs is remarkably increasing with stepping up accumulation of Sugi plantation in Japan, expanding the demands of these logs has become an urgent issue. Because the use rate of domestic lumber to wooden houses in Japan is considerably low, particularly beams with only several percent usages, using Sugi lumber as beams in these houses seems to be an effective measure. However, application of lumber without pith as a member of wooden houses is not necessarily popular, whereas it can be sawed up from large diameter logs with good yields. That is because lumber without pith has been considered to be weaker than lumber with pith. From these background, mechanical properties of flat square without pith, which was obtained from Sugi large diameter logs produced in Miyazaki Prefecture, including comparison with flat square with pith was examined. As a result, flat square without pith is equal to the one with pith both in quality and mechanical properties regardless of cutting or sawing method. This result shows that flat square without pith can be used as beams in wooden houses like flat squares with pith. In order to put it into practical use in the future, short-term performance of the connections; and long-term performance of the members and connections need to be examined.

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I investigated the possibility of finding out the potential domestic wood demand on architectural field by using structural lumber and finger-jointed structural lumber for 2×4 construction method, glued laminated timber and cross laminated timber, which are made from board collected from large-diameter log and low grade log, for the purpose of counteracting disadvantage of over grown log and low grade log. The application of board for instant demand increase is for the market of structural lumber for 2×4 construction method. This market has been practically dominated with imported lumber. On the other hand, the application of board for mid-and-long-term demand increase is for the market of mid-to-high rise building. This market has been dominated by non-wooden structural building. In order to boost the demand increase of board, the development of performance based material standard for stimulating to develop new wood based construction material, and the development of quality standard of board for smooth and simplified transaction, are necessary.

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