Well-respected Bulls farm forester and former New Zealand Farm Forestry Association executive member Denis Hocking writes about Accoya wood, an industry made for New Zealand


It is seldom that we, (NZ), encounter a very promising economic opportunity where we have a competitive advantage, existing technology, environmental and especially carbon sequestration positives, job creation at semi-skilled to skilled levels and diversification opportunities for existing land owners.


Although it might seem hype and oversell, I would suggest that just such an opportunity exists in our forest industry with new, international wood-processing technologies.

Radiata pine plantations have long been the mainstay of our forest industry and have provided a productive source of a versatile timber. While many may argue we are over-dependant on radiata, and that includes me, there is no denying its value to the country.

However, the wood does have deficiencies - most notably lack of natural durability, limited stiffness and in younger wood, potential lack of stability.

Durability has been fixed with various chemical treatments, most notably copper/chrome/arsenic treatment commonly referred to by the trade name "Tanalith".

However, the use of such toxic chemicals creates other problems, notably disposal of such treated timber at end of life. Stability and stiffness are more difficult to correct but are greatly improved by growing trees on longer rotations, 30 years or more.

However, recently there have been significant advances in a technology that offers excellent durability and improved stability for softwoods using low environmental impact chemical treatment.

This may sound counter-intuitive – how do you stop bugs with benign chemicals? The answer, or at least one very useful answer, is acetylation.

Chemists have been acetylating wood in various ways for 100 years, including work at Scion, but recent advances in cheaper synthesis of the acetylating agent, acetic anhydride, has made this a very competitive process.

Well-respected Bulls farm forester and former New Zealand Farm Forestry Association executive member Denis Hocking writes about Accoya Wood, an industry made for New Zealand.
Well-respected Bulls farm forester and former New Zealand Farm Forestry Association executive member Denis Hocking writes about Accoya Wood, an industry made for New Zealand.

They don't seem to be sure exactly why acetylating the hydroxyl groups of the cellulose, hemicellulose and lignin in the wood cell walls makes wood so durable – possibly because it makes these polymers inaccessible to the normal degradation enzymes or perhaps because it excludes water from the wood structures; or both.

However, it turns radiata and other softwoods into class one, top durability timbers with greatly improved stability.

Meanwhile, the acetyl moiety, the key component of vinegar and a universal metabolic intermediate in all living cell carries nothing like the threat of copper, chrome and arsenic.

This new acetylation technology is owned by the British Accsys Group and the product, known by the trade name "Accoya wood", is now being used extensively in Europe.

Uses include canal linings to motorway bridges, decking and exterior joinery. In many of these roles Accoya is substituting for tropical hardwoods and in others it is replacing carbon dioxide-intensive steel and concrete.

Another plus for Accoya wood is its stability. It is still very stable even when painted black and exposed to full sun.


There are plans, or perhaps hopes, to expand into the US market. The reservations centre on the question of whether there is a suitable wood resource to support such expansion.

This is where it gets very interesting for NZ's forest industry. Radiata pine is regarded as the best timber in the world for this process. But not just any radiata pine.

They want clear, knot-free radiata sap wood and finger jointed material is not an acceptable substitute. In other words they want pruned, well-grown radiata pine logs. And where is the best place for pruned radiata pine?

It is right here in New Zealand where pruning has been very much part of forest management for more than 40 years. At present, a number of New Zealand sawmills are supplying significant volumes of clearwood to Accsys and these mills are paying top dollars for good pruned logs.

But there are problems with this attractive prospect. The majority of corporate forest growers have pretty much given up pruning because the accountants who control them decided the premium for pruned over unpruned logs had dropped below the $60+ required to justify pruning.

There has been a general move to quantity over quality for forestry yields, driven largely by the currently buoyant Chinese market for low-grade logs. A long-term industry seems to have been overtaken by short-term thinking. However, the $60 premium for pruned over unpruned logs has now returned and, over the past three years, pruned log prices have been very stable, whereas export log prices have fluctuated widely.


Looking to the future, we need to remember logs exported to China are mostly used for concrete boxing, and probably have limited long-term prospects. By contrast, value-added clearwood/Accoya with a myriad of uses should have much better prospects in a "post concrete pouring economy".

But there will be an inevitable hesitation in investing in wood acetylation if Accsys is not confident an adequate resource of suitable pruned logs will be available. We can certainly provide such a resource if we get out and carry on pruning and thinning our trees. And in the process we can help ensure better/diversified returns for land owners, good employment prospects and more vibrant rural communities.

Forestry is already a much better export earner than sheep and beef farming on a per-hectare basis and the extra value offered by an Accoya chain should further lift forestry returns.