Paleo Slide Sets

Paleo Slide Set: Tree Rings: Ancient Chronicles of Environmental Change

Coring huon pine (Lagarostrobus franklinii) in Tasmania.

The work of a dendrochronologist starts with the collection of samples in the field. The particular problem being addressed will dictate site and tree selection so that trees sampled are sensitive to the environmental variable of interest. Once at the site, there are two ways to obtain tree-ring samples. Most commonly, tree-ring samples are collected using a hand-held increment borer to remove a small core of wood roughly 5mm in diameter from the trunk of the tree, ideally from bark to pith. An increment borer is a hollow shaft of steel with a sharp threaded bit at the tip. A handle fits into the opposite end and is used to turn the borer into the tree. Once the borer has been inserted into the tree, a metal extractor or "spoon" is used to remove the core from the shaft. The borer is then removed from the tree. Most trees are very effective at compartmentalizing and closing the small bore hole, just as the tree would close a natural wound caused by insects, weather, etc. Thus, coring does not cause any serious damage to most tree species. Usually, two cores are taken from each tree to facilitate crossdating and to reduce the effects of ring-width variations related to differences in the two sides of the tree. The number of trees sampled from the site depends on how sensitive the trees are to the environment, but the average is about 20-30 trees. In this slide, an increment borer has been inserted into the trunk of the tree and the scientist is holding the extractor with the core on it.

Photo Credits:
Edward Cook
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY: slides

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