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

Abstract

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 of juvenile, 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 of flowering 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 of vegetative 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.