Environmental & genetic variation in blackwood (Acacia melanoxylon R.Br.) survival, growth, form & wood properties

Australian blackwood (Acacia melanoxylon R.Br.) is a high-quality appearance-grade timber species native to eastern Australia and renowned for its rich heartwood colour. It is grown in plantations in Australia and other countries but with mixed results. This is due in part to variable survival, growth, stem form and wood properties, including heartwood colour. The aim of this project was to determine the potential for genetic improvement of these traits by examining their environmental and genetic control. A review of available genetic resources showed that extensive native population provenance and family seed collections have been made with over 60 progeny trials established in both Australia and overseas. However, there are few published papers, particularly on wood properties. Six family/provenance trials were identified as suitable for use in this project. These mainly contained open-pollinated families from Tasmania. Significant environmental (i.e. trial) and genetic variation in survival, growth, and form were found, with greater genetic variation between families within seed zones than between seed zones. Several mainland provenances were included in some trials and showed that blackwood from tropical Queensland was poorly adapted to survive in cool temperate Tasmania. Narrow-sense heritabilities for early age growth and form were significant, but moderate to low respectively. There were no significant genetic correlations between growth and form traits. Wood properties were measured using stem cores on a sub-sample of 16 Tasmanian families across three 19 year-old trials growing at two sites. One site contained two spatially intermixed trials, with and without a Eucalyptus globulus nurse crop. Significant genetic, environmental and genetic by environmental interactions were 13 found for most wood properties, including heartwood colour. The presence of a nurse crop improved tree form but had an adverse effect on growth and wood colour. Stem diameter was not significantly genetically correlated with any of the wood properties, suggesting that selection for improved growth should not compromise wood properties. While environmental factors clearly affect growth and wood properties, the detection of significant genetic variation in most traits studied indicate that there is clearly potential for genetic improvement of growth, form and wood properties in blackwood.