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Eucalyptus laevopinea for high value hardwood

Dean Satchell's blog
Sunday, May 25, 2014

Eucalyptus laevopinea (silvertop stringybark) is a eucalyptus species that grows really fast and produces a high quality hardwood timber.

It comes from the tablelands of New South Wales and is both cold-hardy and very fast growing. The timber is hard, strong and moderately durable. This makes it suitable for a range of high-value end uses like flooring, outdoor decking and furniture, structural applications requiring good strength and being a decorative stable hardwood could even be used for high-quality furniture.

The tree

E. laevopinea is really quite an amazing tree. It has great form, even better growth rates, is mostly self-pruning and has the best health of any eucalypt I've seen. A good dense crown of leaves means high volumes per hectare and resistence to bugs and possums means good growth rates.

The timber

The timber is pale brown and has a narrow band of sapwood. The sapwood is resistent to lyctus borer, which is an added bonus for internal applications, i.e. no treatment required. The heartwood is moderately durable and thus suitable for outdoor uses such as decking and outdoor furniture. Being a stringybark, the logs are easy to mill with low growth stresses and no shakes. Excellent surface hardness for use as flooring and best of all, fast growth! Good stability means that it doesn't need to be quartersawn and is easy to dry. 

Growth rates

I've seen a few stands of E. laevopinea and they were all of similar growth rates to good radiata pine and the ash eucalypts. The ash eucalypts (e.g. E. fastigata and E. regnans) are non durable and soft, therefore not really of much use except for panelling. This one is far more useful but also grows fast, and from what I've seen could be harvested in only 20 years.

Siting

E. laevopinea is growing well as far south as Otago and has shown to be suitable for most New Zealand climates, even colder sites. It grows really well in Northland so is happy with humidity, unlike many eucalypt species.

E. laevopinea is my pick for hardwood timber where extreme durability is not required. Ground durability would be expected to be limited, but I'm yet to be convinced that naturally ground durable timbers hold higher value anyway.


Tim Rose and Angus Gordon admire a 16 year old E. laevopinea in Northland. The diameter at breast height is 61 cm and the tree is pruned to 8m.


The same tree showing a dense crown of leaves. The crown structure is great for an open grown tree. John Pedersen reckons he only pruned "a few branches off" and the tree was otherwise self-pruning.


On the left E. laevopinea and on the right E. quadrangulata. Both trees are 16 years old, open grown and pruned to 8m. The crowns are a similar size but the E. laevopinea has a DBH (OB) of 61 cm while the E. quadrangulata has a DBH (OB) of 39.75 cm. The E. quadrangulata required significantly more pruning but has still grown well and produces a durable timber.

Lost durable eucalypt trials, Northland

Dean Satchell's blog
Saturday, May 24, 2014

Tucked away in the back-blocks of Northland are two important research trials of durable eucalypts. These trials have been abandoned by the researchers for some time, as happens repeatedly in forestry.  The research is not completed, results are not published and once again nobody learns the lessons these trials offer us. This constantly repeating cycle of reinventing the wheel is all too common in forestry. We do have a difficult industry in that research must focus on the long term, but in practice achieving this has many hurdles to overcome.

The two research trials I'm blogging about are the Eucalyptus pilularis and E. muelleriana species and provenance trials. These two species hold promise for industry because they are both durable hardwoods with considerable potential for a range of high-value applications.

We aren't growing these species on any commercial scale because we simply don't know enough about them to be confident that they are profitable plantation species. What we do know, though, is that the timber is superb. If we could grow them, they are most certainly worth growing for timber. We know these species mill extremely well with little end splitting or movement, we know they season easily with negligible collapse, low shrinkage and are stable timbers in service. We know the logs have very little if any compression core and we know the sapwood content is extremely low and is resistent to lyctus borers.

These are quality hardwood timbers suitable for high-value end uses such as flooring, joinery, outdoor decking and furniture, and even on-farm uses such as cattle rails and posts.

So why have the research trials been neglected? In my view because there isn't enough leadership and motivation within industry to identify and explore opportunities. Perhaps we have become myopic with our traditional focus in NZ on one species, radiata pine.

The species trials

The Eucalyptus muelleriana provenance trial was planted in 1993 on rolling fertile pastoral hill country with clay loam soils. The Eucalyptus pilularis provenance trial was planted in 1997 on a separate site, also rolling fertile hill country with clay loam soils and in pasture. 

Angus Gordon, Tim Rose and myself visited both of these trials in May 2014 and assessed the health, growth and form of the trees.

Eucalyptus pilularis trial block

For a long time I have been preaching that form is a real issue with growing E. pilularis, except where the site is sheltered. In my view E. pilularis just doesn't grow straight enough for profitable commercial forestry. Sure enough, only about 1% of the trial trees in this trial were of really good (i.e. perfect) form with no sinuosity and a central leader all the way to the very top of the tree, and only 50% were what I'd class as useable. A big hurdle, but not one that can't be overcome. Useable trees do yield enough volume of sawlogs to have some value, just not optimum or what I'd like to see. Starting with a higher initial stocking would help - I recommend 1600-2000 sph.

Growth rates were superb, we estimate at least 90% of the growth of the adjacent radiata pine planted at the same time.

 

Well known tree hugger Angus Gordon
beside E. pilularis

Health

 

Health was okay, but the crowns were looking a bit thin, probably because only one small area of the stand has been thinned. The original 3x4 spacing results in tall trees without much crown volume. However, E. pilularis is a monocalypt and we can expect only limited damage from leaf feeding insects, with the added bonus that they are not favoured by possums.

Form

The biggest problem with pilularis is "sinuosity". The trunk gets "a wobble on", most likely caused by fast growth and wind. This is a bit different from the case where the leader has been damaged and a branch takes over as the new leader, which causes similar deviation in form. Sinuosity is caused by the leader not being stable enough to stay straight while growing. We saw both, but this general sinuosity of the stem is the big issue for this species. We also saw plenty of trees with poor form resulting from damage to the leader. This might be caused by cicadas or wind, but is to be expected and overall loss of form caused by damage is acceptable. The value loss caused by sinuosity is not. On the bright side, there were a couple of provenances that had acceptable levels of sinuosity and show potential. We also anticipate that selection and breeding will overcome these high levels of sinuosity.

Growth

No complaints here. The usual variation in growth is to be expected from unimproved seedlines. On average there wasn't much difference between radiata pine and E. pilularis in terms of tree diameters on this site.

Other species

Yep, ForestResearch couldn't help themselves. They planted Eucalyptus nitens (shining gum) and E. fastigata (brownbarrel) in this Northland trial. They're still saying the best growth for fastigata is in Northland, but clearly they are only measuring young trees. We saw several dying and lots of dead trees at year 17.

There isn't a nitens alive now, and about half the fastigata have died. These are not species to be planting in Northland, it is way too warm here for them. We have many high quality species that grow well so why plant these when they produce much lower quality timber? They are both cold-climate eucalypts and should really only be sited in frosty southern climes where warm-climate eucalypts don't grow.

The photo below has the nitens in the foreground and the pilularis behind.

 

E. pilularis thinned a year or two ago at approx 15 years showing
very little end-splitting and about 1 cm of sapwood.		 E. fastigata showing rot that was present in the tree when it
was thinned (Lloyd Gravatt pers. comm.)


 

Nearer to the ridge top, form deteriorates where it catches the wind.

 

Nearer to the bottom of the slope form is much better for the same provenance
 
Prime crop tree suitable for breeding selection 

 

Eucalyptus muelleriana trial block

This site has trees approaching 21 years of age and is on fertile clay loam soils, again in Northland hill country. Form improves down the slope from the windy ridges. The volume of wood is high and because the trees weren't thinned on time and remain at a fairly high stocking, harvest might need to be delayed for another 10 years.

Health

Health was okay, but again the crowns were looking a bit thin as the stand hasn't had much thinning over the years. E. muelleriana, being a monocalypt, means we can expect only limited damage from leaf feeding insects, with the added bonus that they are not favoured by possums.

Form

Again, general sinuosity of the stem in unimproved seedlines appears to be the biggest issue in terms of stand quality and value. We saw plenty of trees with poor form that likely resulted from damage to the leader. This might be caused by cicadas or wind, but is to be expected and overall loss of form caused by damage is acceptable and an area for improvement. Despite unimpressive form, in my opinion this stand is likely to yield greater returns than if it were in radiata because almost everything can be used.

Growth

No complaints here. The usual variation in growth is to be expected from unimproved seedlines. On average there wasn't much difference between radiata pine and E. muelleriana in terms of tree diameters on this site.

 

John Pedersen among his 20 year old trial trees.

Summary

Selection of the very best trees and using these for breeding is essential to commercialising these species. Hardwood forestry in New Zealand, and certainly in Northland, is a commercial proposition well worth pursuing. A grafted seed orchard would be a good place to start.

NZFFA members can access the E. pilularis and E. muelleriana archives where we have more information on these trials.

Disclaimer: Personal views expressed in this blog are those of the writers and do not necessarily represent those of the NZ Farm Forestry Association.

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