March 7, 2006

Plantation macrocarpa just rubbish

Filed under: Cypresses,Timber Growing,Trees — shem kerr @ 12:36 am

When Cupressus macrocarpa was first introduced into New Zealand it was used extensively in farm shelterbelts. Despite the lack of silvaculture, these belts produces good amounts of clear timber, even from the top logs. As high quality indigenous

Elderly macrocarpa plantation, Tahora

timber resources progressively became depleted or locked up in nature reserves, more interest was given to growing plantations of fast growing exotics, such as macrocarpa, to replace indigenous species in the timber market. While untended shelterbelts could readily produce a relatively high percentage of clear timber, purpose planted plantations present a their own set of problems.

One concern has been the (monetary) value of the upper logs. Pruning the butt log when the trunk is quite narrow will allow the tree to produce good clear wood around that core. Typically 80% of the price a grower gets for macrocarpa trees comes from the butt log. Usually it is considered that the returns on pruning the top logs are too low, and these are left unpruned. Large branches growing on the upper part of the trunk leave large knots in timber cut from those logs, and that devalues that timber. Spacing the trees closer together means that the branches dont grow so big, and the knots aren’t as big either, so the timber is worth more than that with big knots, so long as the branches were still alive not too long back from harvest. Where the spacing is close enough the branches die and the bark is occluded and this produces lose knots which also devalues the timber.Big branches are needed to grow good fat butt logs fast. Under a relatively evenly spaced even age plantation stand regime that is tight enough to increase the value of the top logs, butt log diametre growth will be slowed. Some growers consider the rate of growth will be unacceptable, and they have opted to concentrate on pruning the butt log and thinning their stands early, allowing big branches to develop in the crown, and market big butts only.

There are some other factors in spacing of macrocarpa trees. One is the amount of ventilation getting through the stand and the within stand humidity in relation to canker. Another is macrocarpa’s need for nutrient resources and its ability to stay healthy and produce high quality timber at a given stocking rate in relation to a site’s ability to supply nutrients. A third factor is the tree’s ability or inability to copy with its own alellopathic chemicals if tightly spaced.. All in all relatively evenly spaced macrocarpa trees in single species conventional plantations is at least a recipe for low quality and low quantity timber, especially if soil nutrient and climatic issues aren’t properly addressed.

The experience of Robin Wallis, a sawmiller of Inglewood in New Zealand, is that shelterbelt trees give higher quality timber than plantation grown macrocarpa. Shelterbelt trees give more clear wood, even a fair amount in the top logs. Not only that, but the wood quality is better. Also, his preference is for a short fat stem on a tree with a wide crown because it wont get damaged in felling; whereas a tall skinny tree may shatter on impact , particularly over broken ( uneven ) ground.

In a shelterbelt with trees with trees at close spacings within the belt, the branches in the top logs are confined to the outside, often to one side only.In a two row belt, the branches are even more likely to be only on one side: the rest of the top log producing clear timber.

Because there is no competition from other trees either side of the belt, large branches can grow and good fat logs can be grown reasonably quickly. The roots can also go out to soil which isn’t being used by other trees with the same nurient needs; and isn’t saturated with alellopathic chemicals.

All these factors ( ventilation; some amount of shelter, light, minimal competition for nutrients, soil with an absence of alellophathic chemicals ) make for a healthier environment for the tree. Competition within the row encourages height growth and provides a means of minimizing branches to a degree that maximizes clear wood at least silvacultural expense.

Tree belts are just one of the patterns that allow simultaneous close and wide spacing

Sequoia hedgerow Tahora

within the stand. Back to back planting in groups of 2 to 4 trees are another option.

Rather than having trees marching in even formation across the landscape, close-wide allows only planting cypresses on the most favourable microsites, with the governess component on the less favourable places. It also provides plenty of space into which to fell thinnings.


1 Comment »

  1. A very informative sight, well worth the read!

    Comment by Treegrower — August 16, 2007 @ 10:46 am | Reply

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