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Ye, L 2011, 'Growth, crown architecture and wood properties and their responses to thinning in Corymbia citriodora subsp. variegata and Eucalyptus dunnii plantations', MSc thesis, Southern Cross University, Lismore, NSW.

Copyright L Ye 2011


Corymbia citriodora subsp. variegata (CCV) Eucalyptus dunnii are two of the main species planted for commercial plantations in subtropical eastern Australia. These plantations are targeted at pulp production but interest in solid-wood is increasing. However, the two species have only been widely planted since the mid-1990s, and the characteristics of CCV and E. dunnii planted for solid-wood products are not well known, particularly for the more recently planted CCV species. In this study, growth traits and three non-destructive wood properties of acoustic velocity, growth strain and pilodyn penetration were assessed for 9.5 year old CCV and E. dunnii. The results indicated that CCV and E. dunnii were of similar tree size and can be sufficiently large to make the plantations economically viable in a few years. Compared with E. dunnii, CCV had higher acoustic velocity (stiffer wood) but lower levels of growth strain and pilodyn penetration (indicating denser wood). This suggests that CCV could be a good commercial species for eucalypt plantations managed for solid wood products.

In the silvilcultural management of sawlog plantations thinning is often applied to assist with producing larger diameter logs in a shorter rotation. This study examined the unthinned control and two thinning intensities, including 300 stems/ha (SPH) and 600 SPH, implemented at an early age of 7.5 years in plantation-grown CCV and E. dunnii. Growth, crown traits and three non-destructive wood properties were assessed two years after thinning. Both growth and crown traits were influenced by thinning treatments in E. dunnii but only growth traits in CCV. These two species exhibited responses at different thinning intensities, with 300SPH responding for CCV and 600SPH for E. dunnii. Effects of thinning on the three wood properties were small. Furthermore, no strong relationships were observed between growth traits and wood properties. These results suggest that larger diameter trees can be produced through thinning in both CCV and E. dunnii plantations without any degrade in wood quality.

The three wood properties were assessed non-destructively on two opposite aspects of each stem. Variation around the stem for these measurements was inconsistent between species or thinning treatments. It is recommended to measure each wood trait on at least two aspects for the future assessments. On the other hand, the use of pilodyn penetration to determine basic density appears feasible for E. dunnii as the two variables had a strong and negative correlation.