Tasmanian Blackwood Growers Cooperative

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

http://www.blackwoodgrowers.com.au/the-textbook-plantation-blackwood

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.

A recent revisit to the Quilliam property at Smithton to do some pruning was time well spent. All up about 7 hours was spent selecting and pruning the best of the blackwoods in the two block plantings (see initial report). These trees have now been marked and pruned to remove large limbs, trim side branches and remove multiple leaders. These selected trees will receive weed control over the coming weeks as the ground begins to dry out. Oh yes! The new pair of gumboots definitely came in handy. Despite the heavy grass competition some of the trees are showing very vigorous apical growth. There was also some evidence of wattle grub which was a surprise in this wet environment. It will definitely be interesting to revisit these trees in 12 months time for an inspection and annual pruning.

In 12 months time some of the block-planted blackwood will be reaching crown closure, which will be useful in limiting side branch growth and encouraging height growth. It will also mean weed growth will start to slow.

As for the single-row windbreak blackwoods, closer inspection found too few trees suitable for pruning that it wasn’t worth the effort. The combination of exposure to wind and the extraordinary weed growth has meant that these trees are struggling to grow. They will produce an excellent windbreak eventually, but no timber production. Mixing wood production with windbreak objectives is difficult even in good conditions and generally requires multiple-row shelterbelts. On the swampy flats of Circular Head it would be a real challenge.

This is the second of two property reports from my recent trip north. This property is on the swampy flats near Smithton.

The soils are saturated for much of the year and there is little in the way of shelter.

If it was a greenfield site I would have advised caution in planting blackwood for wood production. The exposure to strong winds and the high water table present challenges in growing any trees, let alone tall, straight ones.

The property includes two block planting of almost pure blackwood at 3 metre spacing (1,111 trees per hectare) totalling about 1.5 ha, plus a considerable length of shelterbelt/drainside planting that includes a single row of blackwood at 3 metre spacing. The trees are up to 5 years of age. Protection from stock and wallabies was provided by electric fences and the common, soft-plastic tree guards shown in the picture. Obviously there can’t be too many wallabies about.

Despite the exposure and the rampant grass growth, the blackwoods are showing surprisingly good growth and form, particularly in the block plantings. My first response was “what would these trees look like with some weed control and pruning?” Weed control is certainly a problem when there is free-flowing water over the ground for at least half the year. So a single weed control in summer is needed once the ground has dried out, to get these trees growing quickly. The faster the growth the better the form.

Some of the trees are obviously no longer suitable for keeping due to lack of timely pruning, but there are still plenty of suitable trees from which to select the final crop, given that about 80% of the trees will need to be thinned to waste in the next 10 years.

The owner is unsure how to do the pruning, so I will be going back in a few weeks to help select the final crop trees and get them into shape with Mr. Quilliam’s help (and a new pair of gumboots!!).

Given the high water table and the exposure to strong winds there is a real risk of windthrow and crown breakage at this site. Planting at the higher stocking will help reduce that risk as the trees will quickly reach crown closure and help support each other. The trick will then be to gradually thin the trees at regular intervals, to retain near-full crown cover, while also allowing the trees to grow at the maximum possible rate. Leaving the windward row of blackwood trees unthinned and unpruned will also help provide protection and stability for the block plantings.

The combination of early crown closure, annual pruning and regular thinning should result in trees of excellent growth and form.

What then of the single-row blackwood plantings along the drains? I only saw a small section of these but I suspect tree form will not be so good. Given that part of the objective is for farm shelter, the best management may be to just prune and weed those trees that have the best form, and leave the rest to become big and branchy.  Hopefully the unpruned shelter trees will help support the pruned trees in strong winds.

This blackwood planting was a great surprise. It was great that it is still young enough to be brought under good management. Also great that it demonstrates that even on wet exposed sites blackwood can grow very well. There are certainly challenges and risks ahead with windthrow and crown wind damage, but these are currently balanced by the positives of good growth and form.

I will give an update once the next pruning is completed. Stay tuned.