Sensitivity of leaf unfolding to experimental warming in three temperate tree species

Phenological events are sensitive to climate change, and a clear advancement of spring leaf phenology has been well documented. However, the observed phenological trends cannot be directly used to forecast future changes because the underlying mechanisms are still unclear. We conducted a two-year experimental warming experiment using one-meter-high saplings of birch (Betula pendula L), oak (Quercus robur L) and beech (Fagus sylvatica L.). The main objective of this study was to quantify the temperature sensitivity of leaf unfolding to six different warming levels. The results suggested that leaf unfolding dates were significantly advanced with warming for all species in both experimental years. However, different warming treatments elicited different leaf unfolding responses. At low and moderate warming (