The response of vertical foliage distribution to spacing and species composition in mixed conifer stands in central Oregon

The effects of initial spacing and species composition on vertical foliage distribution were tested in two mixed-species spacing trials in central Oregon. Relative and absolute foliage distributions on individual trees were estimated by building branch-level leaf area models for grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), lodgepole pine (Pinus contorta Dougl. ex Loud.), and ponderosa pine (Pinusponderosa Dougl. ex Laws.) and then estimating foliage distribution for entire crowns. Branch leaf area declined at the base of the live crown in all tree species, reinforcing the importance of accounting for branch position within the crown. Tree-level foliage distributions responded to differences in stand structure imposed by initial spacing and species composition. Foliage distribution also differed by tree social position within the stand. The effect of species composition and tree social position diminished with increasing spacing. Species with differing levels of shade tolerance can be quite plastic in the amount and vertical distribution of foliage in response to stand structure.