Asymptotic height-diameter equations for twenty-four tree species in western Oregon

Abstract

Equations for predicting height from diameter outside bark at breast height (DBH) were generated for 24 tree species in western Oregon. The equations were based on the asymptotic Chapman-Richards function. Because geographic location and site productivity may influence height-diameter relationships, height-diameter measures from 8727 plots were first grouped by site class in each of seven ecoregions. Equation coefficients were derived by weighted, nonlinear least-squares regression. Although species differences in the degree of equation fit were evident, the Chapman- Richards function provided reliable predictions of height from DBH overall. These equations were developed specifically for the ZELIG.PNW forest dynamics model, but they can also be used in other models and in field applications.