Shrinking windows: Asymmetric climatic drivers shorten phenological intervals in subtropical plants

Climate change is reshaping plant phenology, altering not only the timing of key events but also the critical intervals between them. However, the responses of these intervals, particularly the understudied flowering-to-fruiting phase, remain poorly quantified, especially in subtropical systems. Using long-term phenological observations (1964–2019) of 37 woody species in a subtropical botanical garden in Southwest China, we investigated how temperature, precipitation, and sunshine duration influence the leaf-out-to-flowering (LFI) and flowering-to-fruiting (FFI) intervals. Our results show significant shortening of both LFI (2.07 ± 0.53 days per decade) and FFI (3.53 ± 1.24 days per decade) over the past six decades. Among climatic drivers, temperature was the dominant factor shortening phenological intervals, followed by sunshine, while precipitation had minimal influence. Notably, the warming-induced shortening was more pronounced for the flowering-to-fruiting interval than for the leaf-out-to-flowering interval, suggesting that successive phenophases differ in their temperature sensitivity. This differential sensitivity underlies the accelerated compression of reproductive intervals. Our findings highlight that warming-driven asymmetrical shifts in phenophases are narrowing developmental windows in subtropical plants, with potential implications for reproductive success, resource allocation, and ecological synchrony. These results emphasize the need to incorporate multiple climatic factors and phenological intervals into predictions of vegetation responses to ongoing climate change.