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Influence of stocking and density upon growth and yield of trees and stands of Coastal western hemlock Osborn, John E.

Abstract

Variations in western hemlock tree and stand growth were analysed to determine the relative importance of causative factors. Four phases in a stand's life-cycle were investigated (seedling establishment, juvenile growth, early stand formation, and middle-age). Detailed analyses of tree growth were made at the time of early stand formation (25 to 35 years). Stand growth and yield data (15 to 160 years) were analysed by multiple regression methods to ascertain the effects of varying density regimes on time and magnitude of maximum wood volume per acre. In all stands studied, tree height was unaffected by variations in stand density. Detailed analyses of current breast-height radial growth indicated that the factors of antecedent growth, tree d.b.h., stand density, age, and site quality were of decreasing importance in the order listed. Statistically, the best measures of stand density were ratios of crown width and live crown length with total tree height, although stand basal area per acre was only slightly less significant. Stand fertilisation with nitrogen stimulated tree radial growth and changed the relative concentrations of foliar nutrients within the crown. Limited (15 trees) biomass studies indicated that production per unit area of above-ground tree weight (oven-dry) increased linearly with greater stand density. Yield increased directly in proportion to the fraction of area occupied by trees (stocking) and curvilinearly with degree of crowding (stand density) within the area occupied. Mean annual net volume increment did not culminate even at stand densities of 500 square feet of basal area per acre. Both intensive and extensive forest management was discussed. Within the Coastal hemlock zone there could be many advantages for a shelterwood regeneration system and two-storey high forest with western hemlock as a supplementary species.

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