Douglas-fir seedlings: some factors affecting chilling requirement, bud activity, and new foliage production

Abstract

Potted 2-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings were exposed to a range of natural and artificial environments during the fall and winter prior to a 9-week period in an environment designed to permit active shoot growth. Seedling response demonstrated (i) that exposure to a period of short (9 h), mild (20 °C) days prepared seedlings for the beneficial effects of subsequent "chilling" (4.4 °C) temperatures and (ii) that the physiology of dormancy of Douglas-fir seedlings may be adversely affected by environments that differ markedly from those prevailing in the Pacific Northwest during the fall.