This dissertation is focussed on the wood properties of Eucalyptus tricarpa at age 2 and their associated genetic parameters. The results of this report are intended to aid the New Zealand Dryland Forests Initiative (NZDFI) project with E. tricarpa tree improvement work, with the focus being on the reduction of growth strain.

Six traits for E. tricarpa were assessed using 32 families from a breeding trial established in November 2016. The traits were diameter, acoustic velocity (AV), dry density, Modulus of Elasticity (MOE), growth strain and volumetric shrinkage. The genetic parameters analysed were the narrow-sense heritability, genetic correlation and the coefficient of additive genetic variation.

The mean growth strain of E. tricarpa was 1735.00 µɛ, which was less than that of three other species of interest in the NZDFI project. The growth strain had a moderate narrow-sense heritability of 0.32, which means that reducing the growth strain via breeding may be a challenge, however, the CVa for growth strain was 12.32%, meaning that there is scope to manipulate the growth strain.

The genetic correlation between growth strain and MOE was high (0.65), implying a trade-off but this may be offset by the high stiffness wood present in E. tricarpa, which had a mean MOE of 11.35 GPa at age 2. The estimated genetic gain showed that the growth strain in E. tricarpa could be halved (-52%) if the top family was selected but this would be impractical in a breeding programme. Selection for further tree improvement work should consider selecting multiple families based on their breeding value rankings for growth strain, diameter and MOE.

The main limitation of this study was that the environmental effects on the traits could not be assessed and therefore further studies on E. tricarpa wood properties should include multiple sites to analyse these effects.