Time-trajectory of mean phytomass and density during a course of self-thinning in a sugi (Cryptomeria japonica D. Don) plantation

A sugi (Cryptomeria japonica D. Don) plantation was monitored for 20 years to investigate the time course of self-thinning. Mean stem volume (w) increased with decreasing density (ρ), resulting in self-thinning line expressed as lnw=lnK−αlnρ, where K and α are coefficients. The overall slope of the line, if a single straight line is fitted, was −2.17. The slope of the trajectory tended to decrease toward a value of −3/2 with increasing stand age. The phase self-thinning line (Xue et al., 1997) tended to decrease toward a slope of −3/2 with increasing stand age. The time-trajectory of mean stem volume and density was expressed as a mathematical model which incorporates the Tadaki's model into the 3/2 power law of self-thinning. The present model is regarded as a generalized equation in comparison with other published mathematical models.