Paavo Pelkonen

Dormancy release in Pinus sylvestris L. and Picea abies (L.) Karst. seedlings: effects of intermittent warm periods during chilling

SummaryExperiments designed to test three simulation models were used to study the effects of intermittent warm periods during the chilling period on dormancy release in 2-year-old seedlings of Pinus sylvestris L. and Picea abies (L.) Karst. The effect of the intermittent period varied according to its timing. Compared with corresponding continuous chilling treatments, the intermittent periods (1) after 1–3 weeks of chilling increased the proportion of the seedlings for which dormancy was subsequently released, and (2) after 4–7 weeks of chilling substantially diminished this proportion. The intermittent periods did not affect the time required for growth initiation in forcing conditions. These results support a simulation model with a strict end-point for the rest period. On the basis of the experimental results, division of the dormant period into three sub-periods is proposed.