I think these are the sorts of questions that would interest potential and existing blackwood tree farmers. Maybe you could use them as the basis for a post on your WWW site?
a/ We have a range of blackwoods from just planted to some that are in the range 35-60cm+ DBH. The easiest way to determine their growth rate is to measure them over a few years but what would you say we should be looking at as annual DBH increment on these larger trees assuming it’s a good site?
If you are growing sawlogs that a sawmiller can process profitably then the traditional objective is to grow trees that have a diameter at 1.3 metres above the ground (what foresters call “breast height” or DBH) of 60 cm. Obviously not every tree in a plantation will be growing at exactly the same speed, so perhaps the goal is to have >80% of the trees in a plantation >60 cm DBH. Plantations are an investment, and return on any investment starts to drop dramatically once the investment is greater than 40 years. So growing a 60 cm blackwood over 40 years means an average annual diameter increment of 1.5 cm. I would put this as the minimum diameter increment for commercial blackwood. Now it might take a tree 5 years before it is growing at this speed, which means that for a few years at least it will have to grow a bit faster to get the 40 year average. Better still is to grow the blackwoods to 60cm in 30 years which would mean an average annual diameter increment of 2.0 cm. Trees will only grow at this rate on good sites and only if they are well managed ie. thinned to a 7 metre spacing. Exceptional trees will grow even faster than this, and in Chile and New Zealand they can get blackwood growth rates faster still.
If you are doing periodic diameter measurements one suggestion is to mark the stems of the blackwoods with a dab of spray paint so that you are measuring diameters in the exact same spot on the trees each time.
b/ We have a large amount of seed forming on our trees that we could use for direct seeding with some best tree selection. And my sister has some nice silver wattle and blackwoods on her property. What are your thoughts on direct seeding these acacias into some disturbed soil followed by some stem selection in the first few years? Perhaps ten or so seeds into a meter x meter.
Firstly I would ask what you are hoping to achieve by direct sowing that would be better than planting? If you are growing commercial blackwood I can’t see any advantage in direct seeding. In fact it adds complexity and extra effort. Compared to the New Zealand regime of spot spraying and planting at 3.5 metre spacings, direct sowing seems so much more work. For example weed control is always tricky with direct sowing once seedlings are growing, and weed control is essential in getting blackwoods growing quickly. Then there is all that thinning. No! In my opinion it would be better to use the seed by growing it in pots or tubes and planting at regular spacing. This makes management (pruning, thinning and weed control) so much easier.
Bye for now.
Thanks for the questions. I hope my answers provide you with the necessary information. Comments or further questions always welcome.
Happy blackwood growing!