Effects of Species Mixtures and Inventory Zones on Net Yields of British Columbia Forests

Abstract

A least squares procedure developed to determine statistical significance of both qualitative and quantitative data was applied to find proportions of plots and amounts of wood yield by species mixtures and inventory zones. For 9 781 plots in Douglas-fir, spruce, and lodgepole pine forest types, sample volumes were highest in mixtures of these species with other conifers. However, small differences in age, site index, and stand density could account for much of the variation. When stand volumes were brought to common levels of age, site and density the need to recognize species composition classes and forest inventory zones diminished.If indicated gains from mixtures were real, stand managers could easily improve density of pure stands to exceed the increased yields indicated for conifer mixtures with Interior Douglas-fir (20.4%) and with lodgepole pine (3.4%). Because our analyses of regional inventories could not provide conclusive results, well designed long-term field trials would be needed to evaluate effects of species mixtures under fully comparable conditions.When stand density is used with age and site index to estimate yields there should be no need to recognize inventory zones within Coast and Interior races of the species tested.