Growth pattern of tree organs in relation to the process of canopy development in a Cryptomeria japonica stand

22年生スギ林分の20個体について、樹冠下の幹の枝節解析を行うことにより、樹冠底高や樹冠長のほか、地上部各器官の重量、成長量、枯死・脱落量の経年変化を調べ、林冠の発達過程や器官成長様式の推移を議論した。個体の純生産率は、樹冠葉量の増減や樹冠構造の転換により変化し、「減少-安定-上昇-安定」の経過をたどる。このことから、林冠発達過程は、純生産率の変化を根拠として明確に4期に区分される。個体の幹成長への物質配分率は、純生産率と樹冠新葉率の関数として表され、前者が大きく後者が小さいほど高い値をとる。幹配分率は、林冠発達過程の第1期では新葉來の低下により上昇する。第2期以降では、幹配分率は純生産率の影響を強く受けそれと同様の変化パターンを示し、第2期で安定、第3期で上昇、第4期で安定の傾向を示す。第4期における幹配分率は、0.40〜0.65の範囲にあり、個体間差は純生産率の変動にほぼ支配され、上、中、下層木間のちがいは極端な被圧木を除けば明らかではない。Changes with tree age in height to crown base above the ground, crown length, above-ground tree biomass and growth, and litterfall were investigated in a 22-year-old Cryptomeria japonica D. DON stand, by introducing knot analysis. Net production rate on an individual level changes by increases or decreases of crown foliage mass and transformation of the crown structure ; it at first decreases, next, levels off, and after increases, levels off again. Accordingly development of the stand canopy clearly is divided into four different stages on the basis of the changes in the net production rate. The partitioning ratio of photosynthate for stem growth (s) is given as a functlon of the net production rate (E) and the ratio of current-year foliage growth (R) to the total crown foliage, resulting in larger values when E becomes larger and/or R becomes smaller. In the first stage of canopy development s increases due to decrease of R in spite of the decrease of E. After the first stage, however, s is influenced greatly by E, showing the same time-course as that of E ; levels off in the second stage, then increases in the third, and levels off again in the fourth. Values of s in the fourth stage, ranging from 0.4 to 0.65,do not show significant differences among tree height classes, except for extremely suppressed trees