Effect of freezer storage on bud dormancy release in Douglas-fir seedlings

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Abstract
Two-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings from four western Washington and Oregon provenances were lifted from the nursery on December 11, 1979, January 21, February 13, and March 11, 1980, following the accumulation of about 600, 1170, 1550, and 1800 chilling hours (temperature ≤5 °C), respectively. They were tested for bud dormancy (rest) intensity and vigor immediately after lifting and following 2 and 6 months in freezer (−1 °C) storage. Dormancy weakened exponentially with accumulated nursery chilling, with seedlings from all four provenances responding in a like manner. The rate of dormancy release was substantially retarded by freezer storage, so that by late March stored seedlings were more dormant than those remaining in the nursery beds. Dormancy weakened in storage more rapidly in high-elevation provenances than in provenances from lower elevations. Early-lifted seedlings lost dormancy more rapidly in storage than did late-lifted seedlings. Vigor following a 6-week greenhouse trial was good or excellent in all but the December-lifted unstored seedlings and the March-lifted unstored and 6-month stored seedlings.

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