Rethinking the interpretation of spring phenological temperature sensitivity

Recent publications showed a substantial decline in spring phenological responses of temperate trees to temperature increase and suggested this was evidence that warming has caused chilling and/or photoperiod to constrain phenology. We show that the apparent decrease in phenological sensitivity is mathematically expected under warming climates without any constraints from photoperiod or chilling. We substantiate the proposed mechanism using data from controlled conditions, simulations, and a long-term cherry blooming record series.