Early-Season Warming Advances Autumn Senescence in Temperate Tree Saplings in Association With Early Growth Dynamics.

The timing of autumn leaf senescence is driven by external cues such as temperature and photoperiod and is strongly regulated by internal developmental processes. Correlative evidence suggests that earlier budburst and warmer conditions in spring and summer could accelerate development and advance senescence, yet this hypothesis remains largely untested experimentally. We investigated how early-season warming affects growth and senescence timing in three European tree species (Carpinus betulus, Tilia cordata and Acer platanoides). Saplings were grown under ambient or warmed open-top chambers (+5°C) from January to the summer solstice, after which all saplings were maintained under identical conditions. Warming advanced leaf-out by 14-28 days in all species. While height growth was unaffected by warming, radial growth increased significantly in T. cordata and C. betulus. Early signs of senescence (20% leaf discolouration or leaf fall) occurred significantly earlier in saplings exposed to pre-solstice warming in C. betulus (-31 days) and T. cordata (-24 days), with effects weakening but remaining significant at later senescence stages. In contrast, A. platanoides showed no warming-induced changes in growth and senescence timing. Our results suggest that early-season warming can advance autumn senescence, and this response may be associated with species-specific differences in early-season growth dynamics. These findings are consistent with a potential role of growth and carbon dynamics in linking spring conditions to autumn phenology, although the underlying mechanisms remain to be directly tested. Incorporating such developmental processes into vegetation models may improve predictions of growing season changes under climate warming.