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Minimising growth-strain in eucalypts to transform processing

By Dr. Clemens Altaner, June 2019.

Download SWP-T087 (pdf)

Executive summary

A four-year MPI Sustainable Farming Fund project 407602 was undertaken at the University of Canterbury School of Forestry (2015-2019).

  • The driver for the project was the perceived opportunity for high-stiffness eucalypt veneers to be manufactured by New Zealand laminated veneer lumber (LVL) processors. High-value international markets exists for LVL. Eucalypts are well-suited to this end use, because of their high stiffness and homogenous density.
  • Two current constraints which deter manufacturers from using eucalypts in LVL are: (i) growth strain in eucalypts, which causes logs to split when harvested and sawn, and (ii) there is no large-scale, quality eucalypt resource near the processing plants.
  • Both these constraints have the potential to be overcome by the on-going NZ Dryland Forests Initiative breeding programme, which aims to breed genetically improved durable eucalypts as the basis for sustainable home-grown durable hardwood industries in New Zealand’s dryland regions.
  • By identifying the best ‘low growth strain’ genetic material early in the rotation of selected eucalypt species, it should be possible to speed up its incorporation into the NZDFI breeding programme.
  • A series of trials was established, comprising five of NZDFI’s highly durable species of known families.The species planted were E. bosistoana and E. quadrangulata, E. argophloia, E. tricarpa, and E. sideroxylon.
  • The stems of the trees were harvested at age 2 years, with the cut stumps being left in situ following harvest and allowed to coppice. The potential to take cuttings from coppice regrowth therefore remained.
  • Harvested stems were tested for growth strain using a newly developed rapid assessment technique, which enabled very large numbers of stems to be assessed.
  • The sampled trees were assessed for a range of wood properties – growth strain, diameter, density, acoustic velocity, volumetric shrinkage and modulus of elasticity. The heritabilities of, and correlations between, these traits were calculated.
  • The assessments enabled the selection of the most promising families in terms of low growth strain and other properties. Cuttings were then harvested from the coppicing stumps of the top-performing families.
  • The project successfully supported the development of new clonal propagation techniques for the selected eucalypt species by Proseed in Amberley. E. bosistoana clones from top-performing families are now established as stool material for commercial clonal propagation.
  • Cuttings taken from the SFF 407602 trials have been successfully propagated. E. bosistoana produced from propagation have been planted out in two further low growth strain breeding trials, a highly successful outcome.
  • In addition, peeling trials using 30-year-old E. globoidea were undertaken in collaboration with Nelson Pine Industries Ltd. The trials demonstrated that veneers of suitable quality could be obtained from the trees, and also demonstrated the importance of low growth strain to maximise veneer yields.
  • Various outreach activities have been undertaken as part of the project including three international workshops. The project has also been the subject of numerous student theses and academic publications.

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