Abstract

We studied the process by which bud burst of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco) is synchronized to seasonal cycles. Seedlings from 23 populations were treated in 12 growth-chamber combinations of chilling periods and flushing temperatures. Bud-burst rates increased approximately logarithmically with temperature. Rates also depended on the duration of chilling, with temperature coefficients (Q10) increasing from 2.7 after 11 days of chilling to 3.5 after 77 days. The annual temperature cycle, moisture relation, latitude, elevation, and distance from the ocean of the site of origin of a population also influenced the rate of bud burst in the population under controlled conditions. The adaptive significance of these responses is discussed in terms of Levins's dormancy strategy hypothesis.

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