A growth model based on the self-thinning rule

A two-staged stand growth model is developed to describe the relationship between biomass or volume and numbers of stems in even-aged, monospecific plant populations undergoing self-thinning. The model is tested on red alder (Alnusrubra Bong.) seedlings and red pine (Pinusresinosa Ait.) stands grown over a range of site qualities and initial spacings. First, survival rate is modelled as a Weibull distribution. This is then fit to an analytical size–density model to give growth estimates. Crown closure is estimated to occur at a relative density of 0.09 for red alder, while initial mortality is estimated to occur at a relative density of 0.12 for red pine. Net stand growth rates peaked at a relative density of 0.54 for red alder biomass and from relative densities from 0.40 (widest initial spacing) to 0.55 (densest initial spacing) for red pine total stem volume. Site quality merely shifted the magnitude of these relationships. The model adds a dynamic component to the self-thinning rule and also generalizes and extends the rule to stand development between crown closure and the self-thinning asymptote.