Genecology of Bud-Burst Phenology in Douglas-Fir: Response to Flushing Temperature and Chilling

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Abstract
The process by which bud burst of coastal Douglas fir (P. menziesii var, menziesii [Mirb.] Franco) is synchronized to seasonal cycles was studied. 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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