Forestneeds

August 23, 2006

Eucalypts:naturally durable, or easily and profitably grown?

Filed under: Eucalypts,Forestry Research,Timber Growing — shem kerr @ 10:45 am

Carrying on the theme of approaches to growing timber: should it be easy andE_nitens_sapwood_rot
profitable; or should we bang our heads against a brick wall? Take the present enthusiasm for naturally durable Eucalypt timber in New Zealand: what are the trade-offs in growing such species, as against growing less durable or non-durable species?

There will be some generalisations here – and the the picture will be generally correct: useful enough for the purposes of entrepreneurial decision-making.

The more durable species are slower growing and/or require more resources than the less durable ones; they also have more limited or specific choice in siting. It may be easier to get better grades of sawn timber from a lot of the more durable eucalypts than from many of the non-durable ones.

The faster growing species that give a wider choice in siting, are less resource hungry; are less durable; and tend to have problems such as distortion, checking and other downgrade if processed by sawing. In some circumstances some of these faster species may also be more prone to pest attack.
One recent entusiasm has been to replace low strength CCA treated Pinus radiata pineMarlborugh_NZ_vineyard vineyard posts with stronger and naturally durable eucalypt posts.Having looked at these radiata vineyard posts, I can understand why they are breaking. The closest immediate remedy is to use radiata from older denser stronger trees as quarter round posts. The next closest remedy is to use one of the less toxic preservative treatments instead of CCA, to minimise environmental effects. Suppose we do need to use an even stronger timber, then E nitens might be the best choice` – fast grown young trees totally sapwood easily treated. I’ll repeat this for emphasis: E nitens fast growing totally sapwood easily treated with low toxicity chemicals – could be the more profitable alternative to naturally durable eucalypt timber.

Another enthusiasm has been for fast grown short fat butt logs at wide spacings which more easily produced better timber than that from taller thinner trees.E_nitens_boards One could grow a whole lot more timber in a shorter time at closer spacing. In the past this has presented problems when sawing solid timber from the ash group of eucalypts and E nitens.with the latter seen as a chip, pulp, or peeler log species. Collapse, washboard surface, checking and distortion can be common with these species – especially when grown at close spacings which tend to give problems in sawing. New processing technology eliminates these problems.

The traditionally more easily processed naturally durable eucalypt species now have competition: new processing technology; new less toxic chemical treatments; along with totally sapwood short rotation eucalypts.


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2 Comments »

  1. I’m interested in knowing the names of the more durable Eucalypts. Can you tell me which are best for fence posts?

    Michael Evenson

    evenson@igc.org

    Comment by Michael Evenson — February 20, 2007 @ 5:03 am | Reply

  2. It depends. The most durable Eucalypts will give good in ground service for over 30 years. However, these trees only grow in relatively frost free climates. Eucalypts are the marsupials of the tree world; there is a species for every niche throughout Australia. Some for dry sites others for moist climates or soils. Maybe the ‘best’ is the fastest at putting on durable heart wood in your climate. If a durability class 1 Eucalypt wont grow well or at all near you, then try a class 2 or 3 species. Some pointers are given in The In-ground Natural Durability of Australian Timbers http://www.fwprdc.org.au/content/pdfs/PN04.1004.pdf
    Eucalyptus cloeziana and E microcorys are class 1 species that grow fast in suitable climates and produce heartwood early on small diametre trees. If you have a moderate amount of light frost, then a fast growing class 3 species such as E obliqua (around 15 years in ground service) will be the ‘best’. Such trees may need to be grown longer to allow enough durable heartwood to form. Posts may also neeed to be quartered or cut out from larger logs.
    When the climate goes below about -8 degrees Celcius for many days, then you would be better off growing other trees such as Port Orford Cedar; Alaskan Yellow Cedar; or American Chestnut.

    Proceedings of a workshop on Eucalyptus in California June 14 to 16 1983 Sacramento California http:// http://www.fs.fed.us/psw/publications/documents/psw_gtr069/psw_gtr069.pdf gives some pointers to the limitations of growing Eucalypts for timber production in cooler climates.
    A fuller list of references is given in http://forestneeds.com/special-needs/solid-timber-production/eucalypts/

    Comment by shem kerr — February 20, 2007 @ 11:31 am | Reply


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