The contrast in stand dynamics as revealed by comparing parameter estimates for a general stand growth model

Abstract

A general stand model is fitted to and used to describe the pattern of stand dynamics for six different species of conifers. The species considered are Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), lodgepole pine (Pinuscontorta Dougl.), western hemlock (Tsugaheterophylla (Raf.) Sarg.), jack pine (Pinusbanksiana Lamb.), white spruce (Piceaglauca (Moench) Voss), and red pine (Pinusresinosa Ait.). The model, a causal process model, uses two difference equations and six species-specific parameters to generate changes in stand volume and density as a function of volume, density, and site quality. In a simulation framework, the model represents a variable-density, variable-site yield equation. The model's structural equations are invariant from species to species. The differences in species stand dynamics are thus reflected by differences in the species-specific parameter values. The variation in species dynamics is accounted for by variation in only three of the model's parameters. The first of these three parameters reflects the site-determined growth potential of the species, the second reflects the reduction in growth that results from stand crowding, and the third corresponds to a density-independent mortality rate.