@article{oai:soar-ir.repo.nii.ac.jp:00011181, author = {朱, 建軍}, journal = {信州大学農学部演習林報告}, month = {Mar}, note = {Japanese larch (Larix kaempferi Carriere) is one of the most important timber species in Nagano prefecture, and most of them were planted under the plans for short rotation managements. Now, longer rotation managements are required because of wood quality problems in young trees and changes of timber demand. But there are few studies on wood qualities related to long rotation management. In the research, sample trees from 106-year-old Japanese larch plantation were set as main study subject. By analyzing their annual ring structures, characteristics of juvenile and mature wood were clarified, and juvenile and mature wood were compared at effects of radial growth on annual ring indices. Furthermore, lumbers and square-sawn timbers from aged forests were investigated for practical use. 1. The radial variation of ring indices By means of X-ray densitometry, I examined the annual ring structure of sample trees from Saku, as well as Yabuhara and Tera. Results showed that ring width was large near the pith, decreased abruptly with increments of ring numbers and got stable from 15~20 annual rings. The variation patterns of earlywood width in radial direction were agreed with those of ring width. Ring density was low near the pith, and increased with ring numbers, and then got stable from 15~20 annual rings. But in sapwood, ring density tended to decrease. The radial variation of latewood density was similar to ring density. These observations suggested that all of annual ring indices changed greatly near pith and got constant after 15~20th annual rings. Therefore, it should be necessary to distinguish the inner part near pith from outside part when dealing with wood quality. 2. Relation between ring indices and radial growth To examine the differences between juvenile and mature wood, sample trees from Saku and Yabuhara were used. Radial development of tracheid length and ring density was observed. And the relation of the radial growth rate (ring width) with some indices of ring structure was investigated. The results proved that radial variations of tracheid length with ring number could be described by a logarithmic formula, and both plantations reached the demarcation of juvenile and mature wood at age 18. By using the segmented regression method, radial variations of ring density were analyzed. It was found that the demarcation of juvenile and mature wood was at age 15 for Saku and at age 21 for Yabahara. The obtained demarcation ages differed between tracheid length and ring density criteria. In practical use, ring density related closely with strength properties, so the results of demarcation based on ring density criteria were used to divide juvenile and mature wood. It was found that higher growth rate resulted in producing lower density wood in juvenile period, but the wood density in mature period did not decrease even with higher radial growth rate. The basic reason for this phenomenon was that latewood width increased with the growth rate increasing. 3. Tensile strength for lumber In order to testify whether the results obtained from annual ring level might be adapted for lumber level or not, tensile tests of lumber were conducted. Results showed that mechanical properties of lumber varied greatly in radial direction within trees, but all sample trees showed similar trend. There were little differences in dynamic Young's modulus between lumber and small clear specimens, which were cut from non-destructed parts of lumber. On the other hand, there were great differences in tensile strength (TS), and the differences decreased with the increase of ring number, and got constant at about 30 years. The presence and distribution of knots affected greatly on TS. Among knot indices, knot number (Kn) and knot area ratio of maximum single knot (Km) were proved to be effective indices for explaining the effect of knots. The distributions of Kn and Km in radial direction agreed with the variation of TS. These results led that the mechanical properties of both them need about 30 years to reach a constant stage. The period was longer than 15~21 years, the results from annual ring level. 4. Square timber qualities In order to evaluate Japanese larch timbers from aged forest for practical use, I investigated the wood qualities of pithless square timbers, which are usually used as building materials. The knots, warps and Young's modulus were measured after air seasoning. Much more square timbers were obtained from fast-growth trees compared to slow-growth trees. Also, there were much more timbers with less or without knots obtained from fast-growth trees than from slow-growth trees. It was also found that 80% of square timbers crooked and twisted after air seasoning, but the quantity of crook and twist was extremely less compared with boxed heart square timbers sawn from young trees. Young's modulus of timbers from aged trees was higher than from young trees. Therefore, it may be suggested that aged trees have potential to obtain more square timbers with small warps and high Young's modulus compared to younger trees. 5. Conclusions The research steps were as follows. First, by using X-ray densitometry, radial variation of annual ring indices was brought out in annual ring level. Then, juvenile wood and mature wood were divided with tracheid length and ring density, and the relation between growth and wood quality was investigated by distinguishing juvenile and mature wood. Furthermore, the variation of tensile strength in lumber level was examined, and the results were compared with the demarcation ages from annual ring structures. Finally, the quality of square timbers from aged trees was investigated for practical use. The results were summarized as follows: 1) The demarcation of juvenile and mature wood ranged from 15th to 21st annual rings that were estimated by tracheid length and ring density. 2) In mature wood, indices of wood quality kept stable, and fast radial growth did not result in lowering wood quality. 3) Ring density tended to decrease in sapwood. 4) It was necessary for more than 30 years to acquire wood with stable quality from the point of practical use. 5) many quality timbers could be obtained from large and aged trees. Based on the conclusions, it was suggested that forest management should be aimed for long rotation, old age, and large diameter for Japanese larch plantations., Article, 信州大学農学部演習林報告 38: 61-99(2002)}, pages = {61--99}, title = {信州産高樹齡カラマツ造林木の成長と材質}, volume = {38}, year = {2002} }