Thermal Requirements of Spring Phenology and Senescence in European Beech Provenances

Thermal forcing is one of the most important drivers of leaf phenology and can be used to determine species’ phenological requirements. Counting on this, the aim of the study was to quantify the thermal regime and determine how it explains variation in spring phenology and senescence in European beech. To achieve this goal, we analyzed the 44 provenances tested in a common garden experiment established in the Carpathian region of Romania during the 4th series of international beech provenance trials. Using growing degree days and senescence degree days, cumulative precipitation over the previous 14 days, and photosynthetically active radiation as climatic factors, we modeled the spring leaf phenology and senescence, the thermal thresholds of provenances, and the length of the growing season. We found that thermal forcing is the primary driver of provenance phenology, but the other climatic parameters also significantly influence these processes. Significant variation among provenances was observed, but the effect of provenance was weaker than that of year or replication, suggesting that environmental conditions exert a stronger influence on leaf phenology dynamics. The identification of contrasting warming and cooling requirements suggests that, in provenance selection or assisted migration practices, thermal requirements are particularly important alongside growth performance.