Tag Archives: Plantations

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.


Quilliam plantation update

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.

Quilliam plantation


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.

Lambert plantation

This is the first of two property reports from my recent trip north. This is a large mixed farm at Sunnyside. Most of the property is on red basalt soils with reasonable rainfall. Ideal conditions for growing blackwood? Well the situation turned out to be much more complex.

Like many properties the farm contains damp areas, gullies, steep slopes, and rocky knobs that don’t fit with current farm activities. Some of these sites were on a neighbouring property that was bought 3 years ago, having been planted to plantations of pine, Eucalyptus nitens and blackwood. It is obviously very good country for growing pine and nitens, but the blackwood story was more mixed.

There are 4 block plantings of 15 year-old pure blackwood. Until acquired by the current owner, none of these had received any thinning or pruning. Three of these plantings are on a stony ridge top with shallow soils. The result is that these blackwoods are all short, of poor form, and in the worst case have dead tops and are infested with wattle grub (a clear indication the trees have been under drought stress). These three areas are now providing useful stock shelter but have no commercial wood production potential.

The fourth blackwood planting was something of a surprise and shows that the property does have the potential to grow good plantation blackwood. Although planted on an exposed ridge top this site obviously has deep soils that have allowed the blackwood to thrive. Six rows of pure blackwood have been planted at approx. 3 metre spacing between a pine planting on the south side, and a nitens planting on the north side, all are 15 years old. Both the pine and nitens plantings have provided protection for the blackwood from winds on this high ridge. The nitens planting on the north side has also provided shading that has encouraged the blackwood to grow tall and straight. If this blackwood planting had been properly managed at an early age with pruning and thinning it would now be a great example of a successful blackwood plantation. As it is the blackwoods are 15-18 m tall with an average stem diameter of approx. 15 cm, but with most trees having some large branches in the lower stem. The owner is currently slowly thinning this stand to concentrate growth on the better trees.


The farm also contains an interesting range of remnant-native and planted blackwood, including a magnificent remnant pure blackwood stand on a very steep rocky south-facing slope. The growth and form of this native and planted blackwood varied enormously. Some were small and stunted, while others showed great growth potential. South facing slopes and wet gullies did not always have the best blackwood. Soil type and depth were obvious facts affecting growth. The owner also mentioned soil pH. Apparently much of the farm has very acidic soils with pH below 6.0. At this soil acidity many legumes, and presumably blackwood included, show reduced growth and vigour. Agronomists generally recommend neutral to slightly acidic soils (pH 6.0 – 7.0) for best legume growth. I’m not aware of any research where the affects of soil pH on the growth of blackwood or other Acacias has been done, so there is an opportunity for some practical research here.

I definitely found this farm to be a learning experience with the unexpected growth behaviours, and the obvious failures of blackwood planted on the wrong sites and the lack of timely management. But these were countered by the unexpected successes of ridgetop blackwood using shade and shelter. This farm shows plenty of potential for growing good plantation blackwood, but with issues of soil acidity and depth that need to be understood and managed. Where they are an option, lower slopes are preferred for blackwood plantations, rather than upper slopes and ridgetops. This farm still has plenty of areas that are underutilised and could be considered for blackwood plantation. Past experiences and mistakes can be used to help guide future successes.


Carrabin blackwood plantation continued…….


A big part of the blackwood cooperative (if we get funding) will be sharing experiences in growing blackwood, both the successes AND the failures. Only by sharing can we gain greater understanding and confidence.

Having previously reported on this plantation based on photos and emails supplied by the owner I can now provide an update based on my visit in March 2012. This is one of the very few successful blackwood plantations in Tasmania, and is a testament to the care and dedication of the owner Gilles Carrabin. Gilles is not only passionate about his trees, he is a joiner/builder/cabinetmaker with a great love of fine timber.

The plantation is not without problems, but with continued care and management this plantation will eventually produce high quality blackwood timber. Most of the intensive management has been completed. The major task now is to carefully thin the plantation down to a final stocking and watch the blackwoods grow.

Site selection and establishment

The plantation is approximately 0.5 ha in area. Originally I assumed the site was on red basalt soils, but I was wrong. Nevertheless the deep clay loams still support tall eucalypt forest nearby. At time of planting no soil preparation was done, no fertiliser added, but weeds were sprayed. Blackwoods were planted at 2x2m spacing (=2,500 trees per hectare!!) to try and control branching and promote good stem form. Protection for from browsing was provided by mesh fencing around the site and 900mm tall tubular Corflute® tree guards. Trees were mulched. Two different blackwood seed sources were planted. The blackwoods were originally interplanted with Silver wattle as a nurse crop, but these grew so quickly that they were removed after a few years.

The plantation has a cypress hedge on the western boundary which was planted some years prior to the plantation been established. This has provided valuable shelter from the prevailing strong winds, with a single row Eucalyptus nitens hedge planted along the southern boundary. Shelter from strong winds is critical in ensuring good growth and stem form are achieved in plantation blackwood.  Of particular interest is that the blackwoods planted next to the cypress hedge show no signs of reduced growth or vigour from competing with the pre-existing hedge.

Another advantage of the chosen site is that it adjoins a public road, so that come harvest time, access for machinery will be easier.


Gilles has focused enormous effort on ensuring the blackwoods have good stem form and small branches. No thinning has yet been done and there has been little mortality. Every single tree has been pruned to 5-6 metres. This is an incredible effort given that 92% of the existing trees will need to be removed to allow the best 200 trees per hectare grow to final commercial size. Perhaps not the most efficient way to achieve the desired end result, but given the uncertainty and blackwoods reputation as a difficult tree to control, a very understandable approach.

The strong focus on achieving good stem form has come at the expense of diameter growth. The current trees range in diameter from 3 – 20 cm dbh with a probable average of 4-5 cm. This is very small for a 12 year old blackwood plantation, where average diameter growth rates should be about 2.0 cm per year. At age 12 years this plantation should have an average stem diameter of about 20 – 24 cm. At least another 10 years has been added to the rotation length as a result of this conservative approach to management. Thinning of the plantation is now critical to allow the final crop trees to start to put on some serious diameter growth.

The goal is to produce ~200 trees per hectare with an average diameter of 60cm at 1.3m above ground at time of harvest, with all trees straight and pruned to 6 metres.

On the positive side the trees are all very healthy and growing well given the intense competition they must be experiencing. There are many pruned trees with excellent stem form from which to select the final crop trees. With such a high stocking of 2,500 trees per hectare, the trees are tall and thin, which makes them potentially susceptible to windthrow. Gilles will have to thin the plantation in stages over a number of years (say 3 years) to minimise the chance of windthrow. This gives the trees adequate time to become windfirm.

I would also recommend Gilles begin an inventory of his plantation. It is small enough that all trees could be measured for diameter at breast height (1.3m) before any thinning. When he has identified the final crop trees that will remain after the thinning is completed, the pruning history and pruned height of these trees should also be recorded and photographed. This will help future potential buyers know that the pruned sawlogs in the trees are indeed free of branches and knots. The retained crop trees can then be remeasured every 5 years or so, so that Gilles can track their response to the thinning, and understand how blackwood responds to good management on this site.

During the thinning process wood samples (discs) should be kept from any thinned trees that have begun to develop heartwood. These will become valuable in helping determine the heartwood colour range that is likely to be encountered when the final harvest becomes due. Heartwood colour, as well as wood basic density, are two of the most important wood properties determining blackwood value. While we don’t yet know whether wood colour within the tree changes over time, we do know that heartwood colour may or may not vary from the pith to the outer edge of the heartwood as the tree grows. We also know that there is wide tree-to-tree variation in heartwood colour in blackwood (at least some of this variation is under genetic control), so having any information on this at the time of final harvest will be important in negotiating a sale.

Oh yes, and I’m sure the retained trees would appreciate a dose of super phosphate to help them to achieve those greater growth rates.


As I said in the original blog, this plantation shows many positive features, including the use of hedges for shelter, good site selection and establishment techniques, and the importance of dedicated, focused management for the first 10 years. Gilles passion for blackwood is clearly evident. The completion of the task with thinning, plus commencing an inventory, should see this excellent plantation become an inspiration to other Tasmanian farmers wishing to grow blackwood.


Share, learn, understand and grow


A big part of the blackwood cooperative (if we get funding) will be sharing experiences in growing blackwood. Only by sharing can we gain greater understanding and confidence. Here is a great 11-year-old blackwood plantation in north-west Tasmania. I’m writing this blog from just the photo and the owner’s emails. I’m looking forward to visiting the plantation in 2012.

Site selection and establishment

Red basalt soil in a relatively high rainfall area at an altitude of 300m provides pretty good conditions for growing commercial blackwood. I’m not sure what protection from browsing was used but it was obviously successful. Like much of north-west Tasmania the site is an exposed windy ridge. This exposure has been overcome by planting a windbreak on the western side and appears to have been effective so far, although the blackwoods are now getting above the windbreak.


The trees are obviously being pruned.  But the plantation is definitely due for a thinning. At final stocking this plantation will have somewhere between 18 and 24 trees, so clearly a lot of the existing trees will have to go. Once the green crowns close (meet) then the lower part of the crown starts to die due to lack of light. This means the trees are seriously competing with each other and growth is slowing.  It is better to stay ahead of this by thinning the stand to ensure there is no crown die-off and that growth remains at its maximum potential.

The intensive management of blackwood plantations means that competition between trees is not needed to control branching and improve stem form. Instead branches and stem form are managed by pruning. So the focus for commercial blackwood is to prune and keep the trees growing as fast as possible. So a lot of pruning effort here has gone onto trees that will become firewood. Some early expert advice may have helped optimise the management.


A site visit will tell how effective the management has been in creating trees that will continue to grow into valuable sawlogs. Nevertheless it is one of the best examples of blackwood plantation I’ve seen in Tasmania. This is a great example of using shelterbelts in what would otherwise we quite an exposed windy site. There is a lot of exposed ridge-top country in north-west Tasmania that could grow commercial blackwood provided shelter was available. Here is one example of how it can be done.

Thinning the plantation down to final stocking of ~200 trees per hectare will allow the crowns of remaining trees to fill out and maximise the growth potential of the site. The trees are now rather tall and thin so thinning may need to be done in two stages over 2-3 years to minimise the risk of windthrow.

Once I’ve visited the site I’ll provide an update. Thanks to the plantation owner for allowing me to share this story.



The textbook plantation blackwood


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.


Gordon Bradbury.