Incorporation of genetic gain into growth projections of Douglas-Fir using ORGANON and the Forest Vegetation Simulator

Growth models for coast Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco) are generally based on measurements of stands that are genetically unimproved (or woods-run); therefore, they cannot be expected to accurately project the development of stands that originate from improved seedlots. In this report, we demonstrate how early expected gain and genetic-gain multipliers can be incorporated into growth projection, and we also summarize projected volume gains and other aspects of stand development under different levels of genetic gain, site productivity, and initial planting density. Representative tree lists that included three levels of productivity (site index = 100, 125, and 150 ft; base = 50 years) and three initial planting densities (302, 435, and 602 trees/ac) were projected from ages 10 to 60 years under three scenarios using two regional growth models (Stand Management Cooperative version of ORGANON and the Pacific Northwest variant of the Forest Vegetation Simulator). The two models projected similar percentage volume gains for improved seedlots. Seedlots with a genetic worth (GW) of 5% for height and diameter growth were projected to have volume gains of 3.3-5.8% over woods-run stands at 40 years and 2.1-3.2% at 60 years. Volume gains were projected to approximately double when GW was increased from 5 to 10%.