This is the first of two property reports from my recent trip north. This is a large mixed farm at Sunnyside. Most of the property is on red basalt soils with reasonable rainfall. Ideal conditions for growing blackwood? Well the situation turned out to be much more complex.
Like many properties the farm contains damp areas, gullies, steep slopes, and rocky knobs that don’t fit with current farm activities. Some of these sites were on a neighbouring property that was bought 3 years ago, having been planted to plantations of pine, Eucalyptus nitens and blackwood. It is obviously very good country for growing pine and nitens, but the blackwood story was more mixed.
There are 4 block plantings of 15 year-old pure blackwood. Until acquired by the current owner, none of these had received any thinning or pruning. Three of these plantings are on a stony ridge top with shallow soils. The result is that these blackwoods are all short, of poor form, and in the worst case have dead tops and are infested with wattle grub (a clear indication the trees have been under drought stress). These three areas are now providing useful stock shelter but have no commercial wood production potential.
The fourth blackwood planting was something of a surprise and shows that the property does have the potential to grow good plantation blackwood. Although planted on an exposed ridge top this site obviously has deep soils that have allowed the blackwood to thrive. Six rows of pure blackwood have been planted at approx. 3 metre spacing between a pine planting on the south side, and a nitens planting on the north side, all are 15 years old. Both the pine and nitens plantings have provided protection for the blackwood from winds on this high ridge. The nitens planting on the north side has also provided shading that has encouraged the blackwood to grow tall and straight. If this blackwood planting had been properly managed at an early age with pruning and thinning it would now be a great example of a successful blackwood plantation. As it is the blackwoods are 15-18 m tall with an average stem diameter of approx. 15 cm, but with most trees having some large branches in the lower stem. The owner is currently slowly thinning this stand to concentrate growth on the better trees.
The farm also contains an interesting range of remnant-native and planted blackwood, including a magnificent remnant pure blackwood stand on a very steep rocky south-facing slope. The growth and form of this native and planted blackwood varied enormously. Some were small and stunted, while others showed great growth potential. South facing slopes and wet gullies did not always have the best blackwood. Soil type and depth were obvious facts affecting growth. The owner also mentioned soil pH. Apparently much of the farm has very acidic soils with pH below 6.0. At this soil acidity many legumes, and presumably blackwood included, show reduced growth and vigour. Agronomists generally recommend neutral to slightly acidic soils (pH 6.0 – 7.0) for best legume growth. I’m not aware of any research where the affects of soil pH on the growth of blackwood or other Acacias has been done, so there is an opportunity for some practical research here.
I definitely found this farm to be a learning experience with the unexpected growth behaviours, and the obvious failures of blackwood planted on the wrong sites and the lack of timely management. But these were countered by the unexpected successes of ridgetop blackwood using shade and shelter. This farm shows plenty of potential for growing good plantation blackwood, but with issues of soil acidity and depth that need to be understood and managed. Where they are an option, lower slopes are preferred for blackwood plantations, rather than upper slopes and ridgetops. This farm still has plenty of areas that are underutilised and could be considered for blackwood plantation. Past experiences and mistakes can be used to help guide future successes.