Carry-over effects between spring and autumn phenology differ among the world's biomes.

Climate warming alters the start (SOS) and end (EOS) of growing seasons, impacting biotic interactions and biogeochemical cycles, yet the carry-over links between SOS and EOS remain poorly understood, limiting future projections. Using MODIS satellite-derived phenology data for seasonal vegetation and European ground observations for deciduous tree species, we show that an earlier SOS typically advances the EOS [on average by 0.19 ± 0.001 days per day (MODIS) and 0.10 ± 0.002 days per day (ground)], while EOS exerts a weaker influence on subsequent SOS. The SOS-to-EOS effect often outweighed abiotic factors, with SOS emerging as the best predictor of EOS in 34% of pixels (β = 0.27). When predicting SOS, EOS was the primary predictor in only 7.9% of pixels, while preseason temperature dominated in 58% (β = -0.33). More importantly, we identified a dampening interaction, where an increase in one carry-over effect reduced the other. Thus, the SOS-to-EOS effect was twice as strong as the EOS-to-SOS effect in temperate deciduous forests, while the EOS-to-SOS effect was up to three times stronger in boreal taiga and tundra. The observed carry-over effects likely reflect developmental (cell and tissue growth) and stress-related constraints (SOS-to-EOS effect), as well as chilling requirements (EOS-to-SOS effect at high latitudes). These findings highlight how physiological feedback affects phenological responses to climate change, emphasizing the need to integrate plant-internal carry-over effects into future ecosystem models.