Relationships between relative spacing index and the ratio of mean crown length to mean height in Japanese cedar (Cryptomeria japonica D. Don) plantations

This paper describes the relationships between relative spacing index (Sr) and the ratio of mean crown length to mean height (CLH) in Japanese cedar (Cryptomeria japonica D. Don) plantations. In chapter III, the relationship between CLH and mean live crown ratio of C. japonica plantations in Takizawa Experimental Forest of Iwate University (TEF) were examined. CLH was positively correlated with mean live crown ratio (r**2=0.999, n=61), and the median and upper quartile of the difference between CLH and live crown ratio were 0.37 and 0.64 respectively. Therefore, this revealed that the value of CLH was nearly equal to that of live crown ratio. In chapter IV, the relationship between Sr and CLH of unthinned plantations of young C. japonica in TEF were examined by using generalized allometric equation. The coefficient of variation (r**2) of the estimated model was 0.942, which achieved the satisfactory predictor of CLH of unthinned plantations of young C. japonica. In chapter V, the generality of the model estimated in chapter IV was verified with the data of Ando et al. (1968) which had been obtained in relation to several types of density control system. The data of unthinned plantations of young C. japonica in TEF was not apart from the data of Ando et al. (1968), except for the data of sparse management in Obi district, on the Sr-CLH coordinate. Linear model analysis applied several explanation variables indicated that the best model with the smallest AIC was that of Sr as an explanation variable. Therefore, the relationship between Sr and CLH of unthinned plantations of young C. japonica were approximately equal to the relationships of thinned plantations of young C. japonica according to the moderate density control. In chapter VI, the relationship between Sr and CLH of unthinned plantations of young C. japonica was compared with that of dense and mature C. japonica plantations. Linear model analysis applied several explanation variables indicated that the data of dense and mature C. japonica plantations was distributed less than that of unthinned plantations of young C. japonica on the Sr-CLH coordinate. In chapter VII, we summarized chapter III to VI, and the density control system for both unthinned plantations of young C. japonica and dense plantations of mature C. japonica were considered respectively.