Optimum growth initiation time for shoot buds of deciduous plants in a temperate climate.

A model predicting optimum growth initiation times for shoot buds of deciduous plants has been derived from simple assumptions based on maximizing average annual photosynthesis as a function of photosynthetic rates, length of growing season and the probability of late frost. This formulation predicts that optimum bud initiation time is sensitive to the variance in the frost probability but is independent of the average photosynthetic rate. Predicted optimal initiation times are only slightly affected by substantial changes in the length of the growing season (over a considerable change in latitude) except when the growing season is very short. The advantage of maximum frost resistance is also greatest in very short growing seasons. It is pointed out that the optimum time of leaf senescence at the end of the growing season must be based on more complex criteria than the time of growth initiation. Certain difficulties in interpreting bud break data from tree transplant experiments are discussed.