Chilling temperature and photoperiod influence the timing of bud burst in juvenile Betula pubescens Ehrh. and Populus tremulaL. trees

Abstract

• Key message: This research demonstrates that inadequate chilling has the potential to slow both the rate and speed of bud burst of two important European forest species;Betula pubescensandPopulus tremula. • Context: The timing of bud burst in deciduous trees has been widely used as an indicator of spring warming. However, winter chilling conditions can have a significant impact on the timing of bud burst. If trees receive insufficient chilling, there may be a delay in bud burst even if spring temperatures rise. Therefore, it is important to understand the effect of chilling on spring phenology of trees. • Methods: Here, we exposed juvenile (3–6-year old) birch (B. pubescens Ehrh.) and aspen (P. tremula L.) trees to a range of photoperiods, chilling durations and forcing temperatures in controlled environment chambers to assess the impact on the timing of bud burst. • Results: Analysis of variance demonstrated that longer chilling duration resulted in earlier bud burst in both species, and less thermal time was needed to reach maximum bud burst. Therefore, in warmer winters bud burst in spring may be expected to be delayed if insufficient chilling is received. However, longer photoperiod may, at least in part, compensate for shorter chilling duration. These results suggest that models predicting climate warming impacts on phenology should take winter chilling into account when considering the timing of bud burst in deciduous species.