Equations for predicting height to crown base for fourteen tree species in southwest Oregon

Equations are presented for predicting height to crown base (or bole ratio) for fourteen species of trees common to the mixed-conifer zone of southwest Oregon. Nonlinear regression was used to fit a weighted logistic function for each species. The independent variables include height, crown competition factor in larger trees, stand basal area, site index, and diameter divided by height. Although a number of alternative model forms were considered, the logistic function was found to fit the data best. Validation of the model indicated possible difficulties with ponderosa pine and golden chinkapin, but these problems are probably due to inconsistencies in the validation data rather than shortcomings in the individual models