Four years old, four metres tall, and a single straight stem thanks to an annual touch with the secateurs. This is the best tree in a small plantation on my friend’s property near Hobart. I planted this while I was doing my PhD to help keep me sane, and learn the art of growing commercial blackwood.
The site is south facing, with deep sandy loam soils and good soil moisture during summer. Annual rainfall is over 1000mm. There is tall eucalypt forest on the north side of the plantation which provides shading for much of the year. The site is exposed to the west and south, with two major wind storms in the past 4 years causing damage.
There are no native blackwoods anywhere nearby to help demonstrate whether this is naturally a good blackwood site, while silver wattle is locally very common and grows very well. The tall eucalypts nearby include E. globulus and E. regnans, so the site at least has good general tree growth.
Unfortunately the above blackwood is not (yet?) representative of the rest of the plantation, which has proven to be an excellent learning opportunity. In addition to the damage caused by the two wind storms mentioned (yes shelter is important), there was no weed control at the time of planting, which was in the middle of winter (possibly the wrong time to plant). The other blackwoods are gradually becoming established but the process has been slower than expected.
When planted the trees were protected from browsing by a two-strand electric fence (for stock protection), and KBC 1.2 metre tall tree shelters (http://www.southernwoods.co.nz/cart/accessories.asp) for protection from wallabies. Trees were given a dose of super phosphate and trace elements (legumes such as blackwood require a range of trace elements such as molybdenum and boron to function and grow properly). Last autumn each tree had weed control, and so far this spring (with excellent growing conditions) the trees have grown well.
One of my objectives with this plantation was to test a simplified version of the New Zealand blackwood regime. The NZ regime involves planting 800 blackwoods per hectare and then thinning to waste down to a final stocking of 200 trees by age ten years (Nicholas and Brown, 2002). Unless you are addicted to chainsaw work, and need a lot of firewood, that seems to me to be a lot of work and waste for little benefit, given that the trees are intensively managed in that first 10 years anyway. So this little plantation is planted at final spacing of 6m x 7m. No thinning to waste is needed, but any mortality means that the site is not fully productive.
My logic here is that if farmers are to be encouraged to grow commercial blackwood, the task needs to be as simple and cheap as possible. Complexity and extra work just increases the risk that critical management such as weed control, protection, and pruning won’t get done.
So is the above tree the exception that proves that this is not a good blackwood site? Or is it indicative that the site can grow good blackwood, and that poor site selection (lack of sufficient shelter) and establishment (no weed control and wrong time to plant) has resulted in patchy growth? So far I’m optimistic and assuming the latter is the case. More trees are beginning to look like the one above, and its performance just keeps getting better every year.
Sharing of experiences like these (both the successes and the failures) will help create a successful and dynamic Tasmanian blackwood growers cooperative.
Nicholas ID, Brown I (2002) Blackwood: A Handbook for Growers and Users, Forest Research, Rotorua, New Zealand.