© 2003 Heron Publishing—Victoria, Canada
High autumn temperature delays spring bud burst in boreal trees, counterbalancing the effect of climatic warming
O. M. Heide
Department of Biology and Nature Conservation, Agricultural University of Norway, P.O. Box 5014, NO-1432 Ås, Norway (ola.heide@ibn.nlh.no) / Received November 18, 2002; accepted March 8, 2003; published online August 1, 2003
Summary
The effect of temperature during short-day (SD) dormancy induction was examined in three boreal tree species in a controlled
environment. Saplings of Betula pendula Roth, B. pubescens Ehrh. and Alnus glutinosa (L.) Moench. were exposed to 5 weeks of 10-h SD induction at 9, 15 and 21 °C followed by chilling at 5 °C for 40, 70, 100
and 130 days and subsequent forcing at 15 °C in a 24-h photoperiod for 60 days. In all species and with all chilling periods,
high temperature during SD dormancy induction significantly delayed bud burst during subsequent flushing at 15 °C. In A. glutinosa, high temperature during SD dormancy induction also significantly increased the chilling requirement for dormancy release.
Field experiments at 60° N with a range of latitudinal birch populations revealed a highly significant correlation between
autumn temperature and days to bud burst in the subsequent spring. September temperature alone explained 20% of the variation
between years in time of bud burst. In birch populations from 69 and 71° N, which ceased growing and shed their leaves in
August when the mean temperature was 15 °C, bud burst occurred later than expected compared with lower latitude populations
(56° N) in which dormancy induction took place more than 2 months later at a mean temperature of about 6 °C. It is concluded
that this autumn temperature response may be important for counterbalancing the potentially adverse effects of higher winter
temperatures on dormancy stability of boreal trees during climate warming.
Keywords:
alder, birch, chilling requirement, dormancy induction, phenology, photoperiod.
