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Tasmanian Blackwood Growers

Update on the textbook blackwood plantation at age 6 years

A lot has changed since I last wrote about this small plantation south of Hobart in December 2011.

This plantation is an experiment to test a simple approach to growing commercial blackwood. It seems to be working at least in terms of growth and tree form. Success has not been 100% so there is still plenty to learn, but the planting has been sufficiently successful to warrant my continuing support.

Why the simple approach to growing plantation blackwood rather than following the New Zealand or Tasmanian methods?

One of the common problems with farmers growing plantations for wood production is that the silvicultural management (pruning and/or thinning) is often not done properly and/or on time. The plantation becomes a wasted effort. Recognising the limited knowledge and resources that farmers have is important in helping to guarantee success.

Making the task of growing commercial plantation blackwood as simple and easy as possible is an important objective.

15 months ago the largest trees were 4.5 metres tall with single straight stems. But I was concerned that too few trees were doing well. Now at age 6 years the largest trees are 6.0 metres tall, single straight stems, pruned to 2.0 metres with stem diameter at breast height (DBH) of 10.0 cm. Last winter these trees had a dbh of 7.0 cm, so they have increased in diameter by over 2.0 cm this past season! Coloured heartwood should now be forming in the largest trees.

This is a good growth rate and with this good site, with the trees at their final spacing (200 trees per hectare), and with no thinning to worry about, I would expect this growth rate to continue for the next 20-25 years.

The picture below shows some of the best trees. Note that the pole lopper is 2.3 metres tall. Remember the goal is to grow blackwoods that are straight, single-stem and pruned free of branches for the first 6 metres. Three more years of annual pruning and these trees will have reached that goal. Then it will be time to sit back and watch them grow. At about age 35 years these trees will each contain about 1.5 cubic metres of clear premium blackwood timber.

Importantly more of the trees are showing improved growth and form, thanks largely I assume to the regular weed control that has happened over the past 2 years, the annual pruning, and having good growing seasons. Keeping young blackwoods weed free for a 1 metre radius around each tree for the first few years is obviously critical to getting good early growth. And getting good early growth is absolutely essential.

Continued leader training will generally not be necessary on the tallest trees now over 6.0 metres tall (my pruner won’t reach much further anyway). However as experience in New Zealand has shown, it is important to avoid having a major stem fork immediately above the pruned 6m butt log, especially in wind-prone areas. Major-fork splitting is not uncommon in wind-prone blackwood plantations. If a fork-split occurs immediately above the pruned log it will lead to rot and decay in the pruned stem, and a loss of commercial value.

There are still some trees that are struggling to grow or recover from wind damage. Some of these have been replaced with advanced nursery stock blackwood. These advanced blackwood have done surprisingly well, becoming established and showing very good growth. Using advanced stock is not something I’d recommend due to cost and the effort of planting these big trees, but it certainly proved a point – blackwood are incredibly tough and versatile.

This past season has been very dry with no effective rainfall since September. While trees on the upper westerly slope have not grown much this season, the rest of the site continues to grow well, with grass staying green on the lower slopes. It is these dry periods that really help identify the best blackwood sites.

In December 2011 I was concerned that I had misjudged the site, or used poor establishment techniques. Now I am confident that it is a good site, although exposure to strong winds is an ongoing problem. If there was more protection from wind this would be an excellent site. This has been a valuable learning experience with an overall good result, and certainly gives me confidence that the simple approach to growing commercial blackwood can work.

Is anyone interested? I’d love to see some more plantations like this established in Tasmania.



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