INTERFERENCE OF PRUNING WITH ENDOGENOUS GROWTH CONTROL

Pruning is considered to interfere primarily with endogenous growth control of trees, by removing sites of auxin production. Besides their function in apical dominance, auxins appear to act as controller in a control loop, based on the interaction of roots and shoots. Herein, root activity promotes shoot growth, which in turn controls root growth by positive or negative feedback, depending on the concentration of auxins produced by growing shoot tips. Pruning initially results in rejuvenation under both seasonal and life-cycle aspects. However, this primary effect is negated by re-established endogenous growth control (“parachute effect”). Because pruning is but one of several external disturbance variables affecting endogenous growth control, and because endogenous growth control also depends on crop load, pruning must be integrated within general tree management by adaptation of its intensity, method, and timing to the special situation of the respective trees. Whereas dormant pruning can only influence shoot/root, shoot/shoot, and shoot/fruit interactions still to be established in the following season, summer pruning additionally interferes with already existing interactions.