Effects of site productivity on individual tree maximum basal area growth rates of Eucalyptus pilularis in subtropical Australia

Abstract

Inventory data were available from 96 plots of even-aged, monoculture, tall-open forests of Eucalyptus pilularis Smith, aged 2–63 years, growing in sub-tropical regions along the east coast of Australia. A model was developed relating the maximum possible stem basal area growth rate of individual trees to their stem basal area. For any tree size, this maximum increased as site productivity increased. However, the size at which this maximum occurred decreased as productivity increased. Much research has shown that, at any stand age, trees of a particular stem basal area are taller on more productive sites than on less productive ones. Taller trees incur greater respiratory costs to ensure maintenance of the photosynthetic capacity of their canopies; this reduces their growth rates. It was concluded that trees with larger basal areas will have the maximum possible growth rate on a less productive site, whilst trees with smaller basal areas will have the maximum possible on a more productive site. The model developed may constitute the first stage of a complete individual tree growth model system to predict wood yields from these forests.

Modelling individual tree maximum basal area growth rates of five tall eucalypt species growing in even-aged forests

“…The results here suggest that, for the five species considered, it would be practical to develop individual tree growth models that are based on functions that relate maximum growth rates to tree sizes, that is, the functions described in Table 2. The next stage in the development of such models would be to determine the effects on those maxima of changes in site productive capacity and then the effects of inter-tree competition [3,24,44−47]; this has been attempted for E. Pilularis [19,20]. Further work would then be required to extend the model to predict variables of interest to forest management, such as tree height, biomass or stem wood volume; this would often use allometric relationships between those characteristics and stem basal area [33,48−50].…”

“…The next step in model development was to choose a model function that would describe these selected data. West [18,20], and Smith et al [21] have used the wellknown Chapman-Richards function [22] for this purpose. Its form is: ΔBm = aB b -cB (1) where ΔBm (m 2 yr -1 ) is the maximum basal area growth rate that an individual tree with basal area B (m 2 ) may have and a, b and c are parameters.…”