Short Note: Genotype-Environment Interactions for Coastal Douglas-fir Grown to 21 Years Across Western Washington State, USA

This study involves polymix families of coastal Douglas- fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) that were created by crossing parents selected from the Cascade, Longview, Twin Harbors and Vail wild populations of western Washington State. Eight to 10 female parents from each population were crossed using pollen-mixes of males from either the same or different populations. In 1985 these polymix families were planted across six genetic tests located in Cascade, Longview and Twin Harbors (two tests per region). Variance components are reported for over-bark breastheight diameter measured at 21 years (DBH21). Genotype x environment (GE) interactions involving different wild populations of Douglas-fir accounted for little variation in DBH21 across the western Washington regions studied. Interaction involving female parents nested within populations was the most important GE effect; explaining 2% of total variation in DBH21. However, this interaction was of limited practical importance since the superior female parents for DBH21 generally showed good stability across tests. Results from this study support selection of superior coastal Douglasfir genotypes that can produce strong, stable growth across a range of site environments encountered in western Washington.