Plus Tree

Wood density and wood quality are not identical: after the wood quality debacle of the 1990s, the reaction of New Zealand companies has been mostly to extend rotation, aiming to increase the proportion of outerwood in the final crop. But breeders could so improve the trees as to permit growers to follow more tolerable shorter rotations.

One of the first reactions of breeders was to look at the wood quality world. There, wood basic density was presented as the canonical characteristic (Zobel and van Buijtenen 1989 is a classical example). It was not only an important variable but, luckily, there was plenty of variation; it had a high degree of genetic control; and it was easy to assess. Some may argue that it became important because it was easy to assess. Pine breeders around the world started assessing, and breeding for, basic density only to find that the intrinsic quality of trees did not change significantly.

A short detour to understand what happened. Tree breeders make, hopefully, a clear distinction between characteristics that are assessed in progeny trials (termed selection criteria) and the characteristics that we want to breed for (called objective traits). Because we are impatient creatures and time is money, we do not wait until rotation age, but we measure trees from around 6 to 8 years of age.

Stiffness and stability can be explained by basic density (DEN) and microfibril angle (MFA), but the relative contributions of these traits change with age. Thus, in the early life of trees MFA is more important than DEN, while DEN becomes more important in older trees. Life becomes interesting because we have been assessing young trees for DEN (our selection criterion) just when stiffness is dominated by MFA. The correlation between MFA and DEN is far from perfect, so making selection for wood quality problematic. This has changed only recently, with the introduction of operational acoustic velocity screening in breeding programs.

Chemical properties are another example of selection criteria that were neglected for a long time. In the last couple of years there has been a high level of interest in the role of galactans in wood longitudinal shrinkage, a relationship first reported by Stan Floyd (2004) of Weyerhaeuser in the USA. There is also a lot of interest in near infrared reflectance analysis (NIR); it has been in use in Australia for several years (Raymond et al. 2001, for example). We are unlikely to find something if we are not looking for it, and we have not payed much attention in the past.

Lesson: we cannot always rely on ‘the official story’. Complacency about our understanding of wood quality delayed progress for at least ten years. We always need to be open to alternative explanations.

A stopover on the way to China

On 24th September 2007, a Chilean newspaper published an opinion piece by Aldo Cerda, forestry manager for Fundación Chile. Mr Cerda made an interesting observation: Chilean foresters now consider New Zealand ‘a stopover on the way to China’, referring to business trips with stopovers in Auckland. His diagnosis: betting too much on the sale of technological services (consulting, software, etc), a lack of investment, poor processing infrastructure, limited ability to pay for raw materials, over regulation and arrogance. The irony of Mr Cerda’s own arrogance is somewhat comforting.

The purpose of this story is not to annoy people, but to point out that today many Chilean foresters are looking to Brazil with admiration and preoccupation. If you think that 22 years rotations on good Chilean sites are a threat, what will you think when Brazilians turn their attention to solid wood? They are already growing pine on rotations shorter than 20 years in Southern Brazil. This raises the question: Can we afford to continue thinking that 30 years is an adequate ’short’ rotation?

Sorensson and Shelbourne (2005) presented a very interesting graph in the clonal forestry chapter of the NZ Forestry Handbook. They plotted value of logs versus wood stiffness, showing a non-linear relationship. There is a big jump of price when moving from industrial grade to structural wood, which then tapers off for better grades. There is an immense amount (around 50% of volume) of poor performing wood, which derives mostly from corewood.

How do we pull together all this information? We can restate our improvement objective to maximise the value of corewood: as outerwood is already good enough. This simple approach has important implications: as shorter rotations become feasible, the assessment of selection criteria is a lot closer to the objective traits (a bonus) and we can look for trees that meet quality thresholds very early in life. Trees do not need to be spectacularly good on average, but good enough very early on.

Will we adopt this perspective? I do not know, but it is one reason for writing this opinion piece. It offers a chance to regain some competitiveness, although it flies on the face of current thinking that 30 years is short enough.

Epilogue

Coming back to the original question, of course genetics is a good investment if we are aiming for the right objective. However, breeding may not make a difference when considered in isolation. Achieving superior forests will depend not only on good genetics but also on site selection and silvicultural regimes aimed to provide decent wood quality in a reasonable time frame.

Breeders’ objectives can be adapted to include not only biological traits but also technical efficiency characteristics, converting them into improvement objectives. In this way we can value the effect of changing trait averages by any means. This makes the comparison of alternative genetics, silviculture and technology ‘projects’ not only possible but desirable.

This essay could be interpreted as an opinion dealing mostly with radiata pine, but this is far from the intention. Most, if not all, issues are applicable to other species. There have been analogies relating the small number of species in agriculture and the dominance of radiata pine in New Zealand. However, when pushing the comparison with the agricultural world one can see that few people are making a lot of money with staple crops (at least when ignoring subsidies). The money is on the specialty crops and I think that one of our mistakes has been to think of alternative species that will have a role as important as radiata pine’s. Probably a reasonable strategy is to provide diversification targeting niche markets.

Breeding is grounded on a vision of the future and my bet is that that future will be based around short rotations. Thus, when I say a reasonable time frame I mean a short, competitive one. We will have to aim for corewood quality: the rest of the tree will sort itself out.

P.S. This is the second part of an opinion piece published in February 2008 in the New Zealand Journal of Forestry. Read the first part here.

This entry was posted Friday, February 1st, 2008 at 5:34 pm and is filed under objectives, short rotation. Responses are currently closed, but you can trackback from your own site.