Genetic control in the survival, growth and form of Acacia melanoxylon

Blackwood (Acacia melanoxylon R.Br.) is a high-quality appearance-grade timber species native to eastern Australia. Wide variation in its survival, growth and form, together with issues related to site selection and intensive silvicultural management, limit progress in its domestication and commercial development. To determine the effect of genetics on these traits, five blackwood progeny trials in northern Tasmania, Australia, aged between 15 and 19 years were assessed. All trials contained a variety of open-pollinated, single-tree, family collections from Tasmania, with one trial containing a selection of provenances from mainland Australia. Significant genetic variation in survival, growth and form were found. This variation was partly explained by broad scale adaptive differences across the wide geographic distribution of blackwood. Blackwood from the tropical northern range of the species had poor survival in cool temperate Tasmania. Significant differences in survival between Tasmanian seedlots were also observed. Among the Tasmanian seedlots, those from low altitudes grew better than those from high altitudes, while those from the north-east of Tasmania had significantly better growth rates than seedlots from the south-east. Seedlots from the north-west seed zone had intermediate growth rates. Significant genetic differences in the proportion of trees with single stems, and the number of large branches in the lower stem were found between Tasmanian seedlots. Early-age seedlot height was significantly positively correlated with mid-age diameter. Stem form was improved under nurse crops, but even open-grown blackwood had low percentages of trees of excellent form. These results indicate that at the broad scale, climatic matching of seed source with planting site is clearly important, however,