The role of auxin stored in scots pine trunk during spring activation of cambial activity

In a 9-year-old pine girdled during the winter cambial activity was observed below the girdle in the next spring. This indicates that cambial activity was initiated without auxin produced in the spring by buds. The auxin produced in apical shoots successively flows down the stem, where as a result of periodic restriction in transport it remains over the winter till the next year. This auxin of apical origin but locally stored over the winter in the stem is responsible for the activation of cambium before the new flow of auxin produced in the apical meristems arrives. Calculations based on seasonal changes in auxin levels can explain both, earlier spring activation of cambium in the crown and the temporary cambial divisions below the girdle, without assumption of direct auxin synthesis in the lateral meristems.