Intraspecific Competition in a Natural Stand of Betula ermanii

Density and size of naturally regenerated Betula ermanii were monitored for six years in a 100 m2 plot located in Hokkaido, northern Japan. Natural thinning of 10- to 15-year-old trees occurred at a negative exponential rate related to tree volume, demonstrating the −3/2 power rule of self-thinning. Diameter distributions were unimodal at ages 10–13 years and bimodal at 14 and 15 years. Changes in diameter distribution were accompanied by changes in structure, from a one- to two-storied stand. Mortality was highest among smaller trees and where density was greatest. The spatial distribution of trees changed from random to uniform with increased stand age.