Category Archives: Management

Hi Gordon,

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!

On my way back from the north west I called in on Giles Carrabin at Paradise to see how his plantation is going. I last reported on this plantation in March 2012:

https://blackwoodgrowers.com.au/2012/03/11/carrabin-blackwood-plantation-continued/

This plantation is one of the few successfully managed blackwood plantations that I know of in Tasmania and is a real testament to the effort and dedication of it’s owner. It demonstrates a number of unique features including the successful use of shelter in a windy site. Three goats now help keep the weeds and blackberries under control (see the pictures).

The regime is not one I would recommend but full credit to Giles for making it work.

A start has now been made on thinning this plantation down to the final 30 trees (it’s only a small plantation). Already the retained trees are responding to the thinning with obvious crown growth. At least another 100 trees should be thinned from this plantation this season. With plenty of spring rainfall this will be a good growing season.

While a great success this plantation still faces two major management risks:

• Thinning too slowly so that productive green crown is lost. Already some trees are beginning to lose their lower green crown due to increasing competition between the trees. These trees are losing their productive capacity, perhaps permanently. Thinning is critical to keep this plantation fully productive and allow the blackwood crowns to develop a stable wide structure.
• Under thinning resulting in too many small trees that are slower growing. This is a common problem with farm plantations and Giles said he is already finding it hard. Having devoted so much physical and emotional effort to get the plantation to this stage it can be a real challenge to then have to cut down the results of so much effort. This is one reason I recommend a much simpler regime.

Having watched the Blackwood in New Zealand video, the risks of thinning too slowly and underthinning are very real. Poorly formed crowns (with the risk of future crown collapse), and permanent loss of growth potential are a high price to pay after so much effort. As farmer Ian Brown says on the video, beware of becoming too emotionally attached to your trees.

With continued good management this plantation will look fantastic in five years time and be a real inspiration to other Tasmanian farmers.

Giles is now planning to establish another plantation using a similar regime but with a wider (3x3m) planting spacing. With such a labour intensive regime I can only support this move to a lower planting rate.

A recent phone call from Jamie Quilliam meant a return journey to Circular Head for some blackwood pruning and maintenance. I last reported on this plantation in October 2012:

https://blackwoodgrowers.com.au/2012/10/09/quilliam-plantation-update/

But compared to 12 months ago this visit was a completely different experience. A year ago, to my complete surprise, this plantation was showing plenty of potential for commercial blackwood growth despite many obvious challenges. But this year the trees looked pretty unhappy with none of the strong apical growth seen 12 months ago. Had I misjudged the site? Was all that strong early growth just a flash in the pan?

Potential issues are the rainfall (last season was a dry one so there wouldn’t have been so much growth), and weed competition (trying to control grass growth on these wet flats is a real challenge!)

The first day of pruning was under a howling westerly wind, which confirmed that at least one of the challenges here is exposure. Blackwoods don’t enjoy growing on exposed sites, not if you want them to grow tall and straight.

On the second day we had finished the pruning and Jamie offered to show me the 3 hectare remnant patch of swamp forest which is next to one of the blackwood plantings. This remnant bush had cattle grazing through it until 13 years ago when it was fenced off. Since then the forest has recovered surprisingly well. From a distance I could see some very impressive Eucalyptus brookerana. But what surprised me most was as we got closer I began to notice the magnificent swamp blackwoods, 25-30 metres tall with long straight trunks (see picture). Clearly this farm used to support some fantastic blackwood swamp forest.

I suggested to Jamie that he would have more success growing commercial blackwood by actively managing the remnant bush. There is some regeneration but also opportunities for active management (eg. controlling blackberries) and blackwood planting. The lessons learnt in actively managing the remnant bush might then help solve the problems in the blackwood plantation. Jamie wasn’t sure about this idea. He hasn’t reached the stage of being passionate about growing blackwood, not yet anyway!

Obviously shelter and nursing from the surrounding vegetation is an important factor in native swamp-grown blackwood. But has conversion to pasture completely destroyed the commercial blackwood growing potential of this property? Here is the perfect opportunity to find out. Side by side, plantation blackwood and high quality native blackwood swamp forest. From the outset I realised that this property was an experiment in the making. Can we find a way to grow quality commercial blackwood in plantations on this property?