Modelling Maximum Stem Basal Area Growth Rates of Individual Trees of Eucalyptus pilularis Smith
Abstract The growth rate of a tree at any time relates to its size and the level of competition exerted by its neighbors for the resources it needs for growth. This work describes the development of a model to predict the maximum growth rate in stem basal area of Eucalyptus pilularis Smith trees in native and plantation forests of subtropical eastern Australia. It shows maximum growth rates increasing with size until the tree reaches a stem diameter at breast height of 27 cm. Thereafter, maximum growth rates decline progressively as the tree grows larger. Physiological reasons that might describe this growth pattern are discussed. The maxima are shown to be independent of tree age, stand stocking density or average tree size, and the productive capacity of the site on which the forest is growing. Study Implications The maximum possible growth rate in stem diameter of a Eucalyptus pilularis tree growing in subtropical eastern Australia is found to depend only on tree size, not its age nor the productive capacity of the site on which it is growing. It increases until stem diameter reaches a certain size and decreases progressively thereafter as the tree continues to grow. There are interesting physiological reasons that may explain this pattern of growth.