Category Archives: Management

Insects, habitat, dead trees and blackwoods

Here is a post from a grower that may interest some readers:

As well as intentionally planted trees, our area in the Strzeleckis has a lot of blackwood growing as paddock trees, in  roadside verges and so on.

I was clearing out some thistles and blackberries from the verge yesterday. Within about 20 metres along the side of the road I noticed 3 wild bee colonies. These were all Apis mellifera or European honeybee. Although not a native these insects do sterling work in pollination.

All 3 colonies were in hollows in blackwoods. One was in the upper section of a dead blackwood that had fallen over years ago, another was only a few metres away in a hollow of a half-dead blackwood and another was in the remaining trunk segment of a blackwood that had died a while ago and lost its crown and any side branches.

Interesting that all three bee colonies were using blackwood hollows. Some agroforestry commentators suggest leaving an occasional dead tree (if a stem dies or perhaps killed as part of thinning) to form a stag for habitat.

Hi David,
It’s an interesting story, if a bit marginal to what I’m trying to achieve.
Some random responses:
What other trees around where you were have hollows? I suspect mainly blackwoods.
Also blackwoods, once they die, quickly start to rot out, so they are a natural and ready source of hollows, if only short lived before the tree falls and rots entirely.
But I definitely take your point. Leaving dead trees AND logs is important for insect habitat. We humans are too quick to tidy up and leave the forest/road verge looking like a park, rather than a forest with all its litter and chaos – and insects.
What about in a blackwood plantation?
Trees randomly die and fall over. Should we leave a few as habitat? Or will this just build up insect populations that then attack living trees? I don’t know the answer. I suspect that insects that inhabit dead trees are different to those that attack living trees. Perhaps those that live in dead trees are predators of insects that attack living trees. Ultimately the answer will vary depending upon the inclinations of each land owner. Some will give some favour to habitat while others will go for maximum tidiness and “hygiene”.
Thanks for the story.
Cheers,
Gordon

Questions from a grower

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!

Carrabin plantation update 2013

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.

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Quilliam plantation update 2013

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.

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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?

Blackwood Planting Time

It’s planting time. Is anyone thinking of planting commercial blackwood this autumn?

If so please let me know – I’d like to help.

It has been a very dry season so far. Unless we get some rain in the next few weeks it may be too dry to plant in some places this year.

Remember the first rule for successfully growing commercial blackwood is selecting the right site. If you are unsure I can help.

We can actually use the current dry season to help identify good sites. If your proposed planting site still has green grass then that is a very good sign that there is plenty of summer soil moisture. These sites are the best for getting good blackwood growth.

As for the planting regime my recommendation is to keep it simple. Until we gain more experience and confidence in growing commercial blackwood then keeping things as simple as possible is the best place to start.

If you are planting this autumn then your site preparation should be happening now:

1. Protection from browsing by all herbivores is very important. Unless your site is more than about 1 hectare in area, you will need tree guards for each tree. For larger areas you might consider mesh fencing. Work out the costings and see what is your cheapest option – tree guards or fencing.

2. Mark out your site with a 7 x 7 metre grid. This equates to 204 trees per hectare. With this tree spacing there will be no need to thin. Not every tree will survive or prosper with good management I would expect better than 80% success.

3. Do weed control in a 1 metre radius circle at each grid point.

4. You should now be ready to plant.

The best time to plant is from late March through to early May. Again, rainfall and soil moisture will be critical to watch in the coming weeks.

Commercial blackwood plantation – perfect land use and investment for that difficult, weed-covered slope.

Blackwood – An overview

Tgaug06blackwood1
Although this article is now 6 years old it is still a good summary of blackwood growing in New Zealand.
Ian Brown is coauthor of the New Zealand blackwood growers handbook. As a farmer his research has helped define the current success of blackwood in NZ.
His comment about blackwood growth rates in NZ compared vs Tasmania should not be taken too seriously.
Undoubtedly NZ has some very good sites for growing blackwood. But we have yet to really test the potential here in Tasmania.
Blackwood – An overview
New Zealand Tree Grower August 2006

 

Happy reading.

Helping blackwood stay on the straight and narrow

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Research has shown, and certainly my own experience agrees, that blackwood growth rate and stem form are positively correlated. The faster the blackwood grows, the better the stem form and the less pruning is required to create a single straight-stemmed tree. Good growth rates are achieved by good site selection, good establishment techniques and good ongoing management.

But some pruning is inevitable. For a variety of reasons blackwood loses its growing tip and then goes on to develop multiple leaders that need to be managed. Here’s a recent example of form pruning to help keep these blackwoods on the straight and narrow. It’s not hard work, and can be enjoyable.

The following excerpt on blackwood pruning comes from the NZFFA website:

(http://www.nzffa.org.nz/farm-forestry-model/resource-centre/farm-forestry-association-leaflet-series/no-20-australian-blackwood)

There has been an increasing acceptance that pruning is essential in managing blackwood. The method has no resemblance to pruning radiata pine; it is not difficult, but requires a commitment to visit the trees annually during the establishment of the 6 metre stem. There are two stages, which overlap:

·         form pruning

·         clearwood pruning

Form pruning

Blackwoods have poor apical dominance. Periods of stem growth are interrupted by abortion of the shoot tip. When growth resumes, several shoots compete for leadership. A blackwood stem is therefore formed by segments of straight growth which are interrupted by zones of disturbance which contain double or multiple leaders. The aim of form pruning is to identify and remove these competing leaders while they are still small (< 3cm diameter), and this requires an annual pruning visit during the formation of the 6 metre butt log. Long-handled pruners are useful.

Clearwood pruning

The aim is to confine the defect core. Clearwood pruning is done annually, starting at about year 3, and is complete by about year 8. It is carried out in stages, in which the largest branches on the stem are removed first, using a 3cm calliper. The trunk is then pruned to the diameter of your defect core (10 to 12cm). No more than a third of the foliage is removed at one visit. It is recommended that about 3 metres of the crown is left after each lift. Ladders that grip the trunk should not be used.

Perhaps not the best description of clearwood pruning. I would define the aim as controlling side branching, and then to progressively removing all branches from below to a height of 6 metres, while retaining about 3 metres of green live crown after each pruning.