Tree growth and mortality for seventy-four years in a thinning experiment of Abies sachalinensis plantation

In a thinning experiment of Abies sachalinensis plantation started in 1948 (at the stand age of 20 year), diameter at breast height (DBH) and tree height (for sample trees) were measured every five years for 50 years. Four experimental plots were established; unthinned (0.1812ha), two-times thinned (0.101ha), three-times thinned (0.101ha), and six-times thinned (0.2ha). The stand suffered the serious wind damage by a typhoon mainly in the unthinned plot at the stand age of 74 year. Immediately after the damage, DBH and tree height of all individuals in the stand were measured and the damage types were recorded. Combining the previous data of the stand development, tree growth and mortality in the stand during 74 years were analyzed. The number of trees died for 54 years from 20 to 74 year at the stand age was highest in the unthinned plot, and it decreased as the times of thinning increased. In the unthinned plot, more than 75 percent of trees that had been alive in 1948 died for the following 54 years and the size of those dead trees had been relatively small as compared with the survived trees. The trees with DBH of 45 cm or larger appeared only in the six-times thinned plot. The number of trees with DBH of 40 cm or larger was also higher in the more frequently thinned plots. Thus, thinning promoted diameter growth effectively. The stand volume growth had a peak at the stand age of 40 year and showed the gradual decrease after that. The number of damaged trees by the typhoon in the unthinned plot was significantly higher than the other three thinned plot. As for the damage type, more than 80 percent of the damage trees was uprooted. The direction which the uprooted trees fell toward was between west and north, corresponding to the strong southeasterly wind, regardless of the frequency of thinning and DBH of the damage trees. Although the ratio of stem height to diameter and the ratio of clear length to tree height as indices of wind resistance were higher in the unthinned plot as compared with the other plots, wind damage occurred regardless of these two ratios within the unthinned plot.