Intraspecific variation of spring and autumn phenology in Fagus sylvatica

The timing of spring leaf out and autumn senescence needs to be well adapted to the climate at the particular site to ensure precise alignment with the change of the seasons.  From a tree species with a large distribution range covering wide parts of Europe, we would expect substantial variation the phenological characteristic and in the chilling requirements of different provenances. If climate is getting warmer and winters are getting shorter, the local adaptation to might not fit future climate anymore, so that the trees cannot take advantage out of an early start of the growing season or a late warm autumn. In a provenance trial with young beech seedlings, we quantified the differences between spring leaf out and autumn senescence of the provenances and individuals. We further asked which climate parameters were the evolutionary drivers for those phenological characteristics. And we investigated, if there is a correlation between phenological timing and growth, assuming that early flushing and late colouring individuals would utilize the growing season better. The difference between the earliest and the latest provenance in spring leaf out was 8 days and in autumn senescence 17 days. For spring leaf out, we tested for several climate parameters and found that the longer the winter with more days between 0 and 10°C at the place of origin, the later the trees leafed out in our common garden. This climate parameter reflects nicely the often-used quantification of chilling. So, at places were typically more chilling time occurs over winter, the trees developed higher chilling requirements.  But also, the lower the minimum temperature in winter at the place of origin, the earlier they leafed out in our common garden, which is less intuitive. For autumn, eastern provenances coloured their leaves earlier than western provenances if grown under the same climate. The growth of the seedlings will be measured in winter 2023/2024 and will be evaluated in relation to their provenances and to their phenological characteristics in the presentation.