Growth rate of jarrah (Eucalyptus marginata) in relation to site quality in cut-over forest, Western Australia

Abstract

The growth rate of jarrah was measured in 47 plots situated in high and low quality cut-over forest between Mundaring and Collie. Mean growth increments per decade for jarrah in high and low quality forest respectively were: diameter, 1.7 and 1.0 cm; basal area, 1.9 and 0.6 m²ha⁻¹; volume, 11.8 and 2.0 m³ha⁻¹. In high quality forest, diameter increment varied inversely with initial basal area whereas basal area increment and volume increment varied directly with initial number of stems per hectare. In low quality forest, basal area increment varied directly with initial basal area and initial number of stems per hectare. From diameter growth curves calculated with these data the average diameter attained by trees in high or low quality forest after 400 years would be about 70 cm or 50 cm respectively. When only trees with above average increments are considered, 70 cm diameter would be attained after 250 years in high quality forest and 310 years in low quality forest. If only the 25% of the trees with the greatest increments are considered, these figures would be 200 and 250 years respectively.