© 2007 Heron Publishing—Victoria, Canada
Physiological and ecological implications of adaptive reiteration as a mechanism for crown maintenance and longevity
Hiroaki T. Ishii (1, 2), E. David Ford (3) and Maureen C. Kennedy (3)
1. Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan / 2. Corresponding author (hishii@alumni.washington.edu) / 3. College of Forest Resources, University of Washington, Seattle, WA 98195-2100, USA / Received January 31, 2006; accepted May 18, 2006; published online December 1, 2006
Summary
Reiteration is the process whereby architectural units are replicated within a tree. Both immediate (from apical buds) and
delayed (from suppressed or adventitious buds) 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 reiteration
occurs without an obvious external stimulus 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 help maintain crown productivity and increase longevity. These include:
(1) reducing the respiration/photosynthesis ratio; (2) increasing hydraulic conductance to newly developing foliage; (3) reducing
nutrient loss from the tree; and (4) 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.
Keywords:
cellular senescence, crown productivity, hydraulic architecture, longevity, nutrient limitation.
