Evaluating maximum stand density and size–density relationships based on the Competition Density Rule in Korean pines and Japanese larch

Abstract

Understanding the relationship between size and density is an important issue for stand density management in terms of self-thinning in even-aged stands. This study was conducted to determine the maximum stand density and evaluate the size–density relationship based on the Competition Density Rule (C-D rule) for Korean red pine, Korean white pine, and Japanese larch in Korea. The study area covered permanently monitored plots of even-aged plantations established for investigating and modeling long-term growth changes through silviculture. Data were applied using the first inventory within the permanent plots before implementing artificial thinning according to research design. To predict the maximum stem number by species, the C-D rule was applied, and the three-parameter method was shown to be better than the four-parameter method. According to the results based on the C-D rule with three parameters, stand density index by species was 1041 trees (Korean red pine, Pinus densiflora), 1089 trees (Korean white pine, P. koraiensis), and 1005 trees (Japanese larch, Larix kaempferi) in 25 cm of quadratic mean diameter. In the relationship between the maximum stem number and quadratic mean diameter with log–log scale, the intercept for Korean red pine, Korean white pine, and Japanese larch was 10.317, 10.901, and 11.331, and the slope by species was −1.047, −1.214, and −1.373, respectively. To analyze the size–density relationship, the sample plots were classified based on relative spacing and relative density. In regression analysis with log–log scale using the censored sample plot data, maximum size–density relationship was explained the most with quadratic mean diameter rather than mean stem volume and dominant height.