Variation in seed traits, leaf phenology and growth performance among sessile oak provenances from Baden-Württemberg and Alsace

Given the long lifespan of forest trees, their adaptation to climate change may lag behind the pace of global warming. In this context, it is crucial to explore the variation of fitness-related traits. Our study focuses on assessing the adaptive potential of sessile oak (Quercus petraea), specifically concerning seed characteristics, as well as leaf phenology and growth performance of seedlings. To investigate this, we conducted a common garden experiment using seeds sampled from 15 relict and four regularly managed sessile oak provenances in Baden-Wuerttemberg, Germany, and Alsace, France. We observed differences in budburst, with the provenances from higher altitude as well as from the Franconian Plateau flushing up to three days later than the provenances from lower altitudes in the other regions. We interpret this phenological behaviour as the result of adaptation to late frosts, which are more common in cold regions. Additionally, we found significant variation in seedling height. These findings highlight adaptive genetic processes in sessile oak populations and underscore the importance of preserving their genetic diversity as a valuable resource for future adaptation to climate change. Such adaptive differentiation should also be considered in seed sourcing. Taking climate change into account, forest reproductive material originating from colder parts of a provenance region should preferably be used locally and ideally enriched with provenances from lower altitude.