Comparing Crown Growth and Phenology of Juvenile, Early Mature, and Late Mature Metrosideros polymorpha

A large sample of terminal (apical) twigs was marked in a l-yr study of crown growth of juvenile, early mature, and late mature Metrosideros polymorpha Gaud. (Myrtaceae) trees. Populations of terminal twigs in upper crowns ofjuvenile, early, and late mature trees increased by 10%,33%, and 5%, respectively. Vegetative flushing occurred at all times of the year. Length of dormancy before bud-break was variable and not synchronized among twigs. Mature trees showed temporal peaks in flowering that were not the same for early and late mature trees. The greatest differences in crown growth processes among the three life states were associated with intensity offlowering and spatial organization of the region of high vegetative growth. Juvenile trees showed apical control with strong flushing in the upper branches, but a low rate of flushing and a high rate of twig death in the lower crown. They did not flower. Sampled branches of the two mature life states were divided into those that showed an increase in the number of terminal twigs (high growth) and those that did not (low growth). No spatial separation of the two groups was evident. Branches with low growth had higher rates of flowering, and rate of flowering was higher in late mature than in early mature trees. Rates ofvegetative flushing were higher in trees in mature life states than in juvenile trees, indicating no reduction of meristematic activity with aging. In late mature trees, many of the twigs formed early in the sample year flushed a second time, producing inflorescences. Thus, the net increase in the number of twigs in their crowns was very small. termined for each species by a genetically defined architectural plan (Halle et al. 1978), the shape of the crown at any point in time is the result of the processes of birth, growth, and death of subunitary parts (White 1979). Changes in crown shape result from changes in the rates of these subunitary demographic processes. I measured the rates of these processes in the crowns ofjuvenile, early mature, and late mature Metrosideros polymorpha Gaud. (Myrtaceae) trees to compare the activity of apical meristems in these three life states. Romberger (1976) and Borchert(1976a) have suggested that the change from the juvenile to the mature life state might be understood through analysis of these subunitary demographic processes. A few demographic studies of the subunitary parts of tree crowns, other than leaves, are found in the literature. These include field data and theoretical models for conifers (Kin211 1 This research was funded in part by Mcintire-Stennis Grant HAW-00684, D. Mueller-Dombois, Principal Investigator. Manuscript accepted 25 October 1988. 2 This paper is part of a dissertation submitted to the Graduate School of the University of Hawaii in partial fulfillment of the requirements for the Ph.D. degree. 3 Department of Botany, University of Hawaii, Honolulu, Hawaii 96822. CROWN SHAPE is the simplest of characters used to differentiate the life states of trees (Gatsuk et al. 1980). Reduced height growth, loss ofapical control, and reduced geotropism are crown-shaping characters associated with the mature life state (Kramer and Kozlowski 1979). In many species, the cylindrical or conical crown associated with the juvenile life state becomes isodiametric or spherical as the bole develops and then flat-topped in old age. Although this procession of crown shapes is de-