Studies on the wood formation in Pinus luchuensis. IV : Effect of crown amount on the width and seasonal development of the annual ring (Department of Forestry)

枝打や除伐, 間伐などの保育作業が材質におよぼす効果を明らかにする研究の第1歩として, ここでは, 下刈以外の保育がなされていない10年生リュウキュウマツ林分を対象に, 樹冠量の異なる個体の木部形成経過を観察し, 樹冠量の違いが胸高部位の木部形成経過や年輪幅におよぼす影響について検討した。1.形成層の活動期間は葉の着生位置や形成層の単位表面積当りの葉量と相関があり, 樹冠率や単位表面積当りの葉量が大きい試験木ではほぼ1年中形成層活動が行なわれるが, それらが小さい試験木ほど細胞分裂の開始時期が遅れ停止時期が早くなる傾向がある。2.晩材形成の開始時期は, 樹冠率や形成層の単位表面積当りの葉量が小さい試験木では早く, それらが大きい試験木では遅くなる傾向が認められる。3.葉の着生位置や全葉量よりも形成層の単位表面積当りの葉量が細胞分裂の回数や年輪幅と相関があり, 単位表面積当りの葉量が大きい試験木ほど形成層活動が活発になり年輪幅が広くなる。4.形成層の単位表面積当りの葉量の指標(Lwo/D・H)と年輪幅の間にはほぼ直線関係が見られ, 同一林分であれば胸高直径(D)から全葉量(Lwo)が推定できるから, 胸高直径と樹高(H)の測定によって年輪幅の推定や制御が可能なことがわかった。The width and seasonal development of the annual ring of Pinus luchuensis having different amount of crown were investigated. Samples were taken at the breast height throughout one growing season and breast height diameter (D), height (H), clear length, alive crown length and total leaf weight (Lwo) of each examined tree were measured after observation of annual ring formation. Clear length, alive crown ratio and index of leaf weight per unit surface area of cambium (Lwo/D・H; examined tree was considered to be a circular cone) had significant correlations with length of period of cambial activity. In trees having higher crown ratio and larger value of Lwo/D・H (larger crown amount trees), there was no clear rest period in the cambial activity. In trees having lower crown ratio and smaller value of Lwo/D・H (smaller crown amount trees), the cell division initiated in early April several weeks later and stopped in early December two months earlier. Latewood formation began in middle June in smaller crown amount trees and in late August or early September in larger crown amount trees. Number of xylem cells and width of annual ring had higher correlations with Lwo/D・H than clear length, crown ratio, or total leaf weight, and they increased linearly as the value of Lwo/D・H increased. An experimental equation between Lwo/D・H and annual ring was obtained. In the same stand, it will be possible to estimate or control the width of annual ring on the basis of the measurement of breast height diameter and tree height, as total leaf weight can be estimate from breast height diameter