June 5, 2006

Cool climate hardwoods

Filed under: Hardwoods,Timber Growing,Trees — shem kerr @ 3:44 am

What choice is there in high quality hardwoods for growing in cool climates?BranchStubZelkova
There is much more choice available from tropical or sub-tropical forests. Some growing a whole lot faster than cool climate trees. The most durable tropical hardwoods typically have much higher durability than cool climate hardwoods when used in identical conditions. Then why try to compete? Is there even any posibility that the economics stack up against cool climate softwoods?

Traditionally people used construction materials that were close around them. As we go further toward the Arctic Circle choices in durable wood narrow. To a certain extent we can get around that by designing for durability; protecting less durable wood with overhanging eaves; using stone or brick in contact with the ground; designing components and joints to resist decay and to enable easy replacement.

Here’s a partial list, just a few examples of cool climate hardwoods. The cutoff point is rather arbitary:

Nothofagus; Zelkova; Acer; Alnus; Betula;

Castanea; Ulmus; Fagus Juglans; Prunus;

Eucalyptus; Populus; Salix; hazel; Cornus

We can play around with these lists, line them up according to durability ratings, then hardiness ratings, then into growth rate ratings. The trouble is that firstly, cold hardiness doesn’t just have to do with absolute temperature minimums, but rather time temperature treatments. The longer the plant is kept at a low temperature the harder it is on the plant. Secondly, out of season frosts, ie in late spring after the tree has come into leaf, although they may be less extreme than that which the plant is stated to be able to withstand in mid-winter when it’s dormant , these out of season frosts can damage or set back growth.Thirdly wind plays havoc with growth ratings. some smaller leafed trees tend to do better than the large leafed ones; lower trees can do just as well as tall ones in really windy conditions. In extreme conditions stems and bark for weaving might be more appropriate than stems for milling and nailing; Willow Birch and Hazel perhaps.

Zelkova serrata likes a moist climate, buds late in the season (November in the southern hemisphere), and takes the wind run speeds around Taranaki New Zealand as good as Acer pseudoplatagus and better than Castanea , Juglans, Alnus, or Prunus. The wood is light coloured, tough with good flexural strength, and probably as durable as Chestnut or Nothofagus. Zelkova is hard to get to grow straight up; it has a tendency to zigzag up; and throws a multi-leadered crown down low if open grown. These problems may in part be due to silvicultural technique: lack of appropriate spacing and type of governess component in the stand; and nutient inbalance. BranchStubZelkovaThe pruning wounds from large branches take a few years to heal over; a certain amount of rotting of the sapwood occurs at the wound site. This could lead to some core rot. The trick is to get the tree to go straight up and to do that fast and have only small branches to prune off; then after the butt log is established, thin the stand to provide enough space to quickly grow the wide crowns than Zelkova needs.


Zelkova serrata at Inglewood New Zealand 13m tall 27.5cm dbh at 25 years Could’ve done better with shelter and nurients.



  1. am considering growing a block of 6 acreas of hardwood timber trees at Lawrence south of Dunedin it’s on a hill with clay subsoil what do you advise. Thankyou, max button

    Comment by max button — May 2, 2007 @ 11:12 pm | Reply

  2. Advise? No way! Discuss? More likely.

    Max, I’m uncertain as to whether you wanted advice on species choice; on how to go about planting and tending; or whether to bother with planting at all. Before we get to the what to plant, we might consider exactly why we are planting, and how we might grow and manage the trees. Somewhere in there it would be helpful to know more about the where as to aspect and moisture availability.

    If you are looking to profit from quick returns then read Gareth Morgan’s ‘Money doesn’t grow on trees’'t-grow-on-trees_869.html
    Neil Barr, one of New Zealand farm forestry’s most prominant eucalypt enthusiasts, commenting on whether it was profitable to grow eucalypts for timber, said that he didn’t know, but suggested that it was still worth while planting them to make your farm more attractive ( including for resale). My understanding of the situation is that only a tiny fraction of growers of ‘minor’ species are growing such timber at a profit. It may be best to include multiple uses for a hardwood lot, such as amenity for farmstay; or food production eg nuts (walnut, chestnut), truffles (oak), syrup (maples, cider gum), or honey. If you are considering pretty much a timber crop only, then carrying out further processing yourself is lkely to be more profitable, as there is greater profit further up the chain. This may be your only option for post-harvest use, as there less likelihood that a miller will want to pay well for a small woodlot of a minor species.

    Given that you select appropriate species, it will then come down to how you do the silviculture. The make or break of this is in the details. New zealand soils are notoriously unbalanced for optimal growth of most exotic hardwood trees. Keep in mind what the tree is trying to do (at the cellular level) with the available resources; and consider how you can best work with the tree to help it achieve those goals for your profit. Among developments to watch is Ian Hall and Chris Perley’s work on ‘Removing a significant constraint limiting the diversification of the forestry estate’
    Also, NZ is typically windier than most places from where the preferred exotics come. An appropriate conifer component may be useful for shelter. Moisture and exposure differences up and down and across the slope may favour different species on different parts of the hill.

    As to what species, ….come on Max, Give us a bit more detail. I know Lawrence vaguely. I’ve bussed through it; biked through it; even walked through it several times. I haven’t spent the night there.let alone done any forestry around the district. I have slept out near Milton; near Rae’s Junction; and further up the river, and undertaken forestry related activities in these places. So I guess I do know that the climate changes sufficiently so that what might work in one place wont necessarily work 20 km away. Also Max, please tell what species or uses, if any, you were considering, along with site factors.

    Comment by shem kerr — May 4, 2007 @ 2:34 pm | Reply

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