Individual growth change in an old-growth plantation of pinus densiflora after thinning prescription

Abstract

Individual growth change of Pinus densiflora during 8 years after thinning prescription in a 94-year-old plantation was investigated comparing it with an unthinned plantation of the same age and a 140-year-old natural stand, to test whether growth of trees could be improved by thinning, what individual traits would affect growth improvement, and whether it would be possible or not to produce large sized timber in the plantations as found in the natural stand at 140 years. Trees in the plantations were characterized by smaller size (DBH=41 cm, H=25-30 m) than old-growth natural stand (DBH=68 cm, H=30-35 m). H/DBH ratio and proportion of crown length suggested that trees in the plantations were more vulnerable to external disturbance such as heavy snow and had less leaf mass than those in the natural stand. After thinning, about 40% of the trees showed an improved annual DBH increment (by ca. 0.1 cm yr-1), whereas 80% of the trees in the unthinned plantation showed deceleration of DBH growth. Change in degree of competition with neighbors or individual variation in leaf mass did not explain inter-individual variation in growth improvement. Improved growth did not appear to be enough to reach equivalent size to trees in the natural stand at the age of 140 years.