Theory 23/Temperate Forest/Phenology
Leaf-Out Needs Both Cues
The claim
Spring leaf-out occurs when the ratio of accumulated forcing to remaining chilling requirement exceeds a threshold, so warm winters delay rather than advance leaf-out.
01Mechanism
Budburst requires chilling to break dormancy and warmth to drive growth; a short winter leaves chilling unmet, which raises the forcing needed.
02Prediction
Leaf-out should be delayed after warm winters.
03Refutation
Leaf-out tracking spring temperature alone would remove chilling.