Crown profile models based on branch attributes in coastal Douglas-fir

Crown size and crown dimensions are important variables for imparting biological realism to individual-tree growth models. Models for estimating crown profile in Douglas-fir (Pseudotsuga menziesii (Mirb.) France) were developed from attributes of individual whorl branches, including basal diameter, total length, angle of origin, and height from ground. The prediction system consisted of four equations to predict whorl branch basal diameter, branch length, branch angle of origin, and corresponding crown radius. The system is entered with three standard individual tree measurements: diameter at breast height (DBH), total height, and height to crown base. Four approaches were developed for modeling crown profile with this system of equations, distinguished by parameter estimation method, modeling data subset, and the specific form by which whorl branch diameter was represented (mean vs maximum diameter). A system-of-equations parameter-estimation technique (modified three-stage least squares) was applied to account for the correlation of error terms across the equations, and this procedure was compared with ordinary and nonlinear least squares methods. The resulting crown profile prediction systems were evaluated under both theoretical and empirical criteria. The recommended system appears to perform well against validation data on both an equation (branch) level and system (crown profile) level. (C) 1997 Elsevier Science B.V.