Variation in periodic diameter increment of trees in an old sugi (Cryptomeria japonica D. Don) plantation at the base of Mt. Iwate

We investigated the variation in the diameter increment of lower stratum trees in a dense plantation of old sugi with respect to the initial tree size and the competitive interaction among neighboring trees. The base diameter and two competitive interaction indices were used in stepwise multiple regression procedures to model the periodic diameter increment of individual trees. All independent variables were within a level of significance, and they were accepted in the regression model. It was concluded that the diameter increment of lower stratum trees in old sugi plantations was positively and negatively correlated to the initial diameter and the competitive interaction, respectively.高密度状態にあるスギ高齢人工林を対象に，直径成長量の個体間差に及ぼす期首直径と競争指数の影響を検討した。定期直径成長量を従属変数，期首直径と競争指数を独立変数としたステップワイズ法による重回帰分析の結果，期首直径だけでなく，競争指数も有意な独立変数として選択された。下層間伐された林木を試料木としたことが，重回帰モデルにおける競争指数の有意性に関係していると考えられる。結論として，スギ高齢林における下層木の直径成長量は，期首直径だけでなく，光を巡る非対称的競争の影響も強く受けている