Résumé
Several physiological processes controlling tree phenology remain poorly understood and in particular bud
dormancy. Many studies have emphasised the action of chilling temperatures in breaking dormancy. However, the
effect of the preceding summer temperatures has rarely been investigated although there is some evidence that they
may be involved in the settlement and intensity of dormancy as well as cold acclimation. In this paper, thermal
time to budburst in relation to the duration of chilling outdoors, preceding summer temperatures and forcing
temperatures was studied by outdoors experiments in seedlings of Platanus acerifolia, Vitis vinifera, Quercus
pubescens and Castanea sativa. Results showed that temperatures of the preceding summer had no significant
effect on the timing of budburst, P. acerifolia and Q. pubescens showed a very weak response to the duration of
chilling, and the phenological characteristics of each species were found to be adapted to the climate conditions
of its own geographical area. The phenological model used in this study explained 82–100% of the variance of the
data without taking into account summer temperatures. Thus, although summer temperatures may be well
involved in the intensity of dormancy and cold hardiness, they do not significantly affect budburst and therefore
may not need to be considered in phenological models for predicting budburst.