Weakened association between sequential phenological events corresponds to interphase extension

The sequential occurrence of leaf unfolding, flowering, fruiting, foliar senescence and other life-cycle events constitutes a full cycle of plant phenology. Temporal shifts in the seasonal timing of these phenophases have been regarded as key evidence of global environmental change. Most previous studies, however, have focused on the timing of individual phenophases. Little is known about the relationships between changes in timing across sequential phenophases. Here, using in-situ phenological records of major European tree species between 1980 and 2017, we show strong positive associations between consecutive phenophases. In particular, the statistical relationship between the timing of consecutive phenophases is comparable to that of temperature for spring phenological events and substantially exceeds the relationship with climatic factors for late-season phenological events. However, the associations themselves have shifted across years, with a significant decrease in the association between the timing of fruit ripening and autumnal coloration, corresponding to the largest extension of interphase duration. Current process-based phenological models largely overlook associations between consecutive phenological events and their interplay with climate change, potentially leading to biased projections of phenological changes and ecosystem adaptation to future climate change. Seasonal events in temperate deciduous trees, from leaf-out to leaf fall, follow a fixed annual sequence. This study shows that the timing of consecutive events is statistically associated in European trees, but that the association between fruiting and leaf coloration has weakened in some species as the interval between these phases has increased.