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Tree Biomechanics Workshop

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Seminar: Tree Biomechanics Workshop
Speaker:  Brian Kane
Date: 23 March, 2012

Brian was an enthusiastic, knowledgeable and passionate speaker who presented a physics based seminar on tree biomechanics. Brian explained at length that he did not need the delegates to understand the mathematics behind the physics; but more importantly to grasp the concepts of assessing trees utilising the theories he presented.

There were 4 basic areas that were covered during the presentation.

  1. How pruning affects wind drag on a tree, tree movement and overall tree dynamics. Pruning a tree is always going to be a compromise between the mechanical and biological requirements of the tree. As arborists we need to maximize the impact of pruning in regards to risk reduction; while minimising the impact on tree health and the level of reactive growth. Consideration should be given to how streamlined a tree becomes during major wind events. The less ‘drag’ on each branch (or the tree as a whole), the less likely it is to reach its bending moment or failure point.
    The idea of a trees potential to become streamlined should be considered during pruning events. For example, a branch with an ‘elbow’ or acute angle is less likely to bend or be flexible enough to become streamlined during major wind events.
    Obviously, lion tail pruning should still be avoided as it extends the centre of gravity, stresses the tree and adversely impacts overall tree health and structure.
  2. Trunk defects and co-dominant stems were also discussed and Brian showed us examples of his field testing in regards to failure of trees under load, from which he put forward the following: Defects increase stresses on a tree under load (wind) through the reduction of the surface area through which the force of the load is spread. For example, a tree whose trunk is evenly hollow, with only 25% sound wood; has 56% of the strength of a fully sound trunk; a tree with co-dominant stems is 80% weaker than a sound union; and under load, a co-dominant stem will fail before the main trunk; unless a trunk has > 80% decay (loss of sound wood).
  3. Cycles of failure for ropes used in rigging systems in tree pruning/removal. Brian trialed a rigging rope rated at 4500kg, the rope was shock loaded 500 times, after which a load of 1,130 kg broke the rope; after 1000 times, a load of 770 kg broke the rope. Certainly food for thought when considering how often we should rotate our lowering lines.
  4. Dangers of using ascenders to access trees. The footage Brian showed us during this part of the presentation put shivers up my spine. A climbing line was put under shock load (approximately 75 kg, dropping 1 m), with the load attached to an ascending device. The ascender stripped the line and the load fell further than 2 m. All ascenders have manufacturer’s instruction as to what type and diameter of rope can be used. A back up attachment should always be used in conjunction with

    ascending devices, even with the right ropes being used.

I thoroughly enjoyed the seminar and found it very informative. Brian used footage of in field trials that he was involved in and backed up the findings with good sound reasoning. A great day was had by all and I look forward to further seminars from overseas presenters, to get a different perspective on the industry and general arboricultural principles.

Brian Kane

Director Glenn Waters in conversation with a seminar delegate

Office Manager Lee Carr making some shop sales

 

What a great spread!.... delegates feast at lunch time

Director Stephen Frank takes a breather with Brian Kane

Brian in action

 

A great turnout

 

 


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