Effects of species mixing on maximum size–density relationships in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.)-dominated mixed forests converted from even-aged pure stands

Abstract

IntroductionDensity management is a key silvicultural tool in management programs that enhances compositional and structural diversity and hence forest growth during the conversion of even-aged pure stands into mixed forests.MethodsTo determine the optimum stand density, a model of maximum size–density relationships was employed to explore the relationship of the self-thinning trajectory with growth, species mixing, latitude, and site conditions during the transition of even-aged pure Chinese fir stands to Chinese fir-dominated mixed forests using stochastic frontier analysis. Data were obtained from a total of 591 permanent plots located in Fujian, Jiangxi, Zhejiang, and Anhui provinces in southern China.ResultsThe results showed that (1) the slope of the maximum size–density relationship of Chinese fir-dominated mixed forests increased and plateaued over time; (2) the slope of the maximum size–density relationship of Chinese fir-dominated mixed forests did not deviate from Reineke’s assumed universal slope of -1.605; and (3) mixing proportion had a positive effect on maximum size–density relationships, and latitude and site conditions had the opposite effect on maximum size–density relationships.ConclusionsOur findings will provide valuable guidance for the forest management of areas in which even-aged pure stands are being converted to mixed forests (i.e., when broadleaved tree species are planted after thinning to improve overall stand density and promote stand growth).