Tree Physiology 27: 455-462, 2007.
Summary Reiteration is the process whereby architectural units are replicated within the tree. Both immediate and delayed reiteration can be seen in many tree species where architectural units ranging from clusters of shoots to entire branches and stems are replicated. In large, old trees and suppressed trees,delayed adaptive reiteration occurs without obvious external stimuli such as defoliation or traumatic loss of the branch apex. This suggests that, in trees that are growth-limited, reiteration is an adaptive mechanism for crown maintenance. We discuss theories about the aging process and how delayed adaptive reiteration may affect their operation to maintain crown productivity and increase longevity. These include: (i) change in the respiration/photosynthesis ratio; (ii) increasing hydraulic conductance to newly developing foliage by altering hydraulic architecture; (iii) reducing nutrient loss from the tree; and (iv) rejuvenating the apical meristem. The ability to reiterate various architectural units may contribute to increasing lifetime reproductive output by prolonging tree longevity. Further studies on the physiological and ecological implications of reiteration are needed to understand its adaptive significance in the life history of trees.