Late frosts weaken spring leaf onset carryover effect on autumn senescence

Frosts occurring after spring leaf onset significantly jeopardize tree growth, forest productivity, and ecosystem functions. As the climate warms, earlier leaf onset has become increasingly common, exposing plants to heightened risks of frost damage. However, the impacts of spring frosts occurring after leaf onset on later senescence phenology in deciduous forests remain largely unexplored. Using 20 years of remotely sensed phenology data, we demonstrate that, in European beech forests, late spring frost events disrupt predictable patterns of leaf onset and senescence, weakening the carryover effect between the start and end of the growing season. Interestingly, the frequency and intensity of these frost events did not significantly exacerbate this disruption. In contrast, favorable summer conditions were found to partially restore the natural interdependency between leaf onset and senescence. Our findings reveal how plant phenology is profoundly affected by climate change not only as an emerging process but also in terms of its internal dynamics. We aspire for our study to lay the groundwork for highlighting the key role of biological start-end of season carryover effects in the phenology responses to climate change, advocating for their incorporation into the development of phenology models.