Regions at high latitudes and high altitudes are undergoing a pronounced asymmetric warming with higher warming rate in winter than in spring. Asymmetric warming in winter and spring makes predictions of the spring phenology responses of plants to preseason winter and spring warming challenging, which in turn limits our ability to understand future ecosystem changes. Previous studies have reported inconsistent results including advances, no changes and delays in the spring phenology of trees during past climate warming worldwide. We will explore whether these different results are caused by an unbalanced relationship between forcing and chilling effects (i.e. variation in chilling effects due to winter warming and changes in forcing effects related to spring warming) related to carbon resource availability.