Assessing plant phenological changes based on drivers of spring phenology

Understanding plant phenological responses to climate warming is crucial for predicting changes in plant communities and ecosystems but difficult with sensitivity analysis that is not linked to drivers of spring phenology. In this article, we present a new measure phenological lag to quantify the overall effect of phenological constraints including insufficient winter chilling, photoperiod, and environmental stresses, based on observed response and that expected from species-specific changes in spring temperatures, i.e., changes in spring forcing (degree days) from warming and average temperature at time of species events. We applied this new analytical framework to a global dataset with 980 species and 1527 responses to synthesize observed changes in spring phenology and investigate the contributions of forcing change, growth temperature, and phenological lag to differential phenological responses reported previously.