Abstract:

The paper presents taper models based on two parameterparsimonious functions，the modified Brink function and the Pain function，for describing stem profiles of Eucalyptus grandistrees. The models were developed from data gathered from Eucalyptus forests grown for sawtimber in the warm temperate granitic Lowveld region in South Africa. The two taper functions provided satisfactory fit to the data set. A small bias was found at different relative heights. Parameter parsimonious functions are promising，as there is a theoretical possibility for developing a generalized stem model using parameter prediction. Parameter prediction was not successful using the modified Brink function. It is always possible and even necessary to develop a parameter prediction model with the help of the Pain function，because the function describes absolute stem diameter as a function of relative stem height. Therefore，a test was made to evaluate，if the parameter prediction functions describe real form differences or only dimension differences. It was found that in this application the parameters might not describe the tree form differences.

Key words: stem profile model, Brink function, Pain function, Eucalyptus grandis