Effect of thinning on allometry and needle-age distribution of trees in natural Abies stands of northern Japan

We tested the effects of thinning on allometry and needle-age distribution in natural stands of Abies sachalinensis Masters by comparing a thinned stand to an unthinned, control stand. Specifically, we attempted to clarify how allometry was altered after a thinning. We assumed that the needle-age distribution of trees in the thinned stand would show a younger composition than in the control stand, given the effect of improved light conditions on needle dynamics following a thinning. These investigations were conducted in dense Abies stands located in central Hokkaido, northern Japan, 19 years post-thinning. In the thinned stand, the ratio of individual needle mass to stem mass increased significantly, as compared to the control. A difference in the H–DBH relationship between the stands was probably related to this tendency. Mean needle age of trees differed significantly between the two stands, and the thinned stand showed a younger needle age than the control. Within each stand, dominant trees showed older mean needle age than codominant or suppressed trees. These tendencies may have been caused by differential needle dynamics affected by light conditions in the stands, and by different crown positions among the trees within a stand. In summary, trees in the thinned stand showed increased growth rates after thinning, which were caused by increased needle mass, younger composition of needles, and improved light conditions.