Küstenbiologie - Coastal Biology

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Shipworm countermeasures Prevention 1: the timber

Prevention 1: the timber

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It is necessary to think about prevention of shipworm attack when choosing materials. For example, after years of heavy infestation you hardly find wooden pilings in the Western Baltic. They were replaced mainly with steel pipes from offshore industries covered with plastic tubes. Recycling plastic has also been evaluated, but so far it was not implemented in numbers.

For wooden materials you can establish a sort of resistance hierarchy (for the types used in Northern Germany):

 

  1. Pine
  2. Larch
  3. Oak
  4. Oak with bark
  5. tropical timbers

 

Big oak pilings mostly last for centuries, but there also were incidents where fresh pilings were destroyed after only two years, just like larch pilings ore pine groynes. Matters are complicated by the fact that different species of oak are in use, and that even individual trees can differ due to the location, where it grew. Still, oak is the best local timber, especially when it can be used with the bark intact. Indeed the shipworm resistance depends more on the chemical content than on the hardness of the wood itself. These "secondary metabolites", tannins in case of oak trees, are concentrated in the bark. Also, the elasticity of the bark and the small gab between bark and sapwood act as a physical barrier.

Tropical timbers are no panacea. Like with oak the hardness of tropical timbers is less important than metabolites. Theses are produced only when needed, so that trees that for example never were attacked by termites are quite likely to be less useful against shipworms. There is a large number of tropical timbers that have been investigated and classified according to resistance, but due to variety of new species and geographical variation the relevance of recommendations is questionable. Also, only sustainably obtained timbers are to be imported (FSC = forestry stewardship council).

Last Updated on Friday, 28 January 2011 12:27