Frost hardiness as acquired by Douglas-fir seedlings in three Pacific Northwest nurseries

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Abstract
Two-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings from two seed sources raised in three nurseries in Oregon and Washington were tested for differences in frost hardiness between September 1985 and January 1986. The objective was to determine whether nursery location significantly influenced hardiness. Seedlings were tested by whole-plant freezing to various temperatures, followed by six evaluations of frost hardiness of needle, bud, and stem tissues. Seedlings at the highest nursery had the hardiest needles and those at the coastal nursery the least hardy needles. Bud hardiness, calculated over time, differed between seed sources but not among nurseries. Stem acclimation followed the pattern of needle hardening from November to January. A regression equation calculated to predict frost hardiness from climatic data and elevation of the nurseries showed that elevation, photoperiod, and number of days of frost were the most important independent factors (R2 = 0.29).

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