Predicting the Effects of Silvicultural Regime on Branch Size and Crown Wood Core in Douglas-Fir

Abstract

Abstract Three major determinants of wood quality in Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) were estimated from the dynamics of crown structure in ORGANON, an individual-tree, distance-independent growth model. Branch whorl locations were estimated directly from the height growth predictions assuming formation of one whorl per year. Mean maximum branch diameter was predicted as crown base receded past each whorl; branch diameter estimates were based on current depth of the whorl into crown, tree diameter, stand relative density, and site index. Diameter of crown wood core was established as diameter inside bark, likewise at time of crown recession past each branch whorl. This approach facilitated description of harvested log distribution (40-ft butt logs) by various branch size, whorl frequency, and crown wood core indices. Based on projections of a 9-yr-old Douglas-fir stand to final harvest at 65 years, thinning precommercially to 121 trees/ac at age 9 resulted in a BD4 (mean of four largest branch diameters per log) of 2.5 in., vs. 1.5 in. for the unthinned stand (484 trees/ac). When thinned to 121 trees/ac, approximately 55% of the volume/ac in 40-ft butt logs consisted of crown wood as opposed to 30% at 484 trees/ac. Responses to subsequent thinnings were less pronounced, but included larger branches in the largest 80 trees/ac, and larger total crown wood percentages for a given initial stand density. Thinning from below resulted in larger average BD4's and slightly greater crown wood percentages than proportional thinning. Individual-tree growth models that contain a crown recession component can easily be modified to predict crown wood core and indices of branch size. For. Sci. 37(5):1409-1428.