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Did you know? - Edge trees – can't live with them, can't live without them

 

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Trees growing on the edge of a stand (photo on left) can grow quite differently compared to trees within a stand (photo on right). Obvious differences include branch size and height, however the differences extend to important wood qualities.

The bad news

Wood quality is negatively affected in edge trees. Solid Wood Innovation (SWI) trials have confirmed that all the wood properties known to be associated with stiffness (density, micro-fibril angle and % latewood) are adversely affected close to the stand margin. It is estimated that edge trees have 10% lower stiffness on average compared to trees within the stand. Edge trees are also shorter, more tapered (see figure 1 below) and have larger branches. Similarly there is a tendency for resinous characteristics to be more prominent along stand edges.

Figure 1: Tree taper with distance from the edge of the stand (averaged and smoothed data). Highly tapered trees occur 0-5m from the stand edge.

The good news

Edge trees are generally bigger; they have bigger diameters and more volume. So long as there is good segregation of log qualities it is possible to avoid sending logs with negative wood qualities to log purchasers and log processors who can't get value out of them. Also, the negative wood quality impacts decrease quickly from the stand edge; 5 to 10m into the stand (depending on the property concerned).

What can we do to minimise the negative impact of lower quality edge trees?

There are a number of management practises to address this issue:

  1. Good land preparation and planting practises that result in an even stocking of trees over all the plantable area – minimising gaps minimises the amount of stand edge.
  2. Well-managed thinning that results in even and appropriate stocking. Clumpy thinning can result in partial edge effects if the distance between trees gets too great.
  3. When undertaking standing timber inventory (such as sample plotting for volume and quality assessment), make sure the stand edge is appropriately represented in the sampling.
  4. Good log making to ensure all logs are in specification (at least visually).
  5. Non-visual segregation techniques such as log sonic measurement can identify low stiffness associated with edge trees to ensure logs are sent to the right log processor.