Racial variation in Eucalyptus nitens reviewed

A young plantation of Eucalyptus nitens (shining gum) at Surrey Hills in north-west Tasmania.

Eucalyptus nitens (shining gum) is widely planted in temperate regions of the southern hemisphere, principally for pulpwood production. It is the second most widely planted hardwood species in Australia and the main species currently planted in Tasmania.  The species is distributed in Victoria and NSW with various races identified on the basis of geography and genetic differences (Hamilton et al. 2008).  A meta-analysis summarising the performance of these E. nitens races and the closely related E. denticulata in 85 field trials across the world was published recently (Hamilton et al. 2011).

The meta-analysis used published and unpublished data from nursery and field trials.  The field trials were in Chile, China, Italy, Lesotho, New Zealand, South Africa and Zimbabwe, and were planted in both summer- and winter-rainfall environments.  Data were available from a considerable number of trials for growth traits (73 for diameter), but information was also available on wood-properties, tree-architecture, fitness and morphological/developmental traits. Meta-analyses were undertaken on these data to gauge the significance of differences among races across trials as well as the race × rainfall zone interaction.

The juvenile foliage of E. nitens (shining gum) has closed apical buds (shown).  This is a key trait that differentiates this species from E. globulus (blue gum) which has an open apical bud at this stage.

The meta-analysis only detected a significant race × rainfall zone interaction for growth traits. In general, Central Victorian E. nitens populations outperformed New South Wales E. nitens populations in winter-rainfall zones, but this ranking was reversed in summer-rainfall zones. On average, E. denticulata grew less rapidly than the best-performing E. nitens races, particularly in winter-rainfall zones. Differences among the E. nitens races were detected in basic density, a commercially important trait, but these differences were small in magnitude. Significant differences among races were also evident in branch size and stem form (straightness). Eucalyptus denticulata races had significantly thinner branches than all E. nitens races except the Southern Central Victorian race, and Central Victorian E. nitens races generally had the straightest stems. The small number of trials represented for most traits limited the power of meta-analyses but where significant differences among races were detected these are likely to represent consistent and robust differences across a broad range of environments.

This meta-analysis of genetic-based trait differences between the E. nitens races completes our review of the genetic resources and breeding (Hamilton et al. 2008), and quantitative genetic diversity both within (Hamilton and Potts 2008) and between ( Hamilton et al. 2011) races of this important forestry species. 

References
Hamilton MG, Potts BM (2008) Review of Eucalyptus nitens genetic parameters. New Zealand Journal of Forestry Science 38, 102-119.
Hamilton M, Joyce K, Williams D, Dutkowski G, Potts B (2008) Achievements in forest tree improvement in Australia and New Zealand - 9. Genetic improvement of Eucalyptus nitens in Australia. Australian Forestry 71, 82-93.
Hamilton M, Dutkowski G, Joyce K, Potts B (2011) Meta-analysis of racial variation in Eucalyptus nitens and E. denticulata. New Zealand Journal of Forestry Science 41, 217-230.