Efficiency of Tree Crowns and Stemwood Production at Different Canopy Leaf Densities

Abstract

Variation in the unit leaf rate in trees, i.e. the weight of wood increment per unit of leaf area, arises from disproportionate changes in their rates of net photosynthesis and in the allocation of carbohydrates. Changes in unit leaf rate in response to variations in canopy density were investigated in a thinning experiment established in a 36 year-old Douglas fir forest. Tree growth was estimated from increment cores and leaf area by linear correlation with sapwood basal area. Net assimilation and mean growth of individual trees expressed as basal area and volume decreased in direct proportion to increase in canopy density from 3.6 to 12.0 m ² m ⁻² of projected leaf area. These relationships were linear with multiple correlation coefficients (r ² )≥0.97. Net stand increment, in contrast to unit leaf rate, culminated as projected leaf area approached 6 m ² m ⁻² and decreased at the higher canopy densities due to mortality. The approach developed in this paper could be applicable in predicting growth in response to various silvicultural treatments.