Dominance of plasticity in wind-pollinated trees' flowering time response to temperature

Climate change is shifting the flowering phenology of wind-pollinated trees, leading to longer pollen seasons and heightened allergy risks. Accurately forecasting these phenological shifts requires a clear understanding of the underlying mechanisms and variations in the sensitivity of phenology to temperature. Here, we investigated the temperature sensitivity of flowering phenology in 74 wind-pollinated tree species across the US using long-term herbarium records spanning over a century. We found consistent phenological responses to spring temperature variations over space and over time in 77% of species, indicating that these long-lived trees can rely primarily on plasticity to cope with temperature variation across different regions. Sensitivity estimates were consistent across both century-scale and decadal time scales, challenging the previous understanding of declines. Interspecific variations in sensitivity exhibited a strong phylogenetic signal, indicating evolutionary conservatism in phenological responses among related species. Together, these findings shed light on the magnitude, mechanism, trend, and variability of temperature sensitivity of wind-pollinated tree flowering phenology. Our results improve the mechanistic basis for forecasting phenological shifts and their downstream effects on airborne pollen and allergen exposure under ongoing climate change.