Here we have tree-ring samples from two trees that grew not too far from each
other. Notice how the patterns for both are the same except that, for one, the
rings are compressed, which shows that it had a slower growth rate. There could
be any number of reasons for the difference—perhaps the tree that produced
the compressed sample was shaded by other trees, for example.
There is a way to present tree-ring information that allows easy comparison of
trees with different growth rates. Called skeleton plotting, it offers other
advantages as well.
Every tree-ring sample contains a record for every year of growth. That's an
awful lot of information, especially if what you want to do is crossdating.
Some of this information is more relevant than other information. Narrow rings
occur less often than normal-width rings, for example, so that information is
What the skeleton plot does is to extract the most pertinent information and
record it on a graph.
Each vertical line in the above graph represents one year. The yellow bars that appear on three
of the graph's lines represent narrow rings. The narrower the annual ring, the longer
The plot records other information as well. The "b" indicates a year with an unusually
wide tree ring, for example, while a dashed line (not seen in this graph) would mark
a year in which that tree failed to produce a visible ring.
With skeleton plotting, tree-ring scientists are able to accurately crossdate
To find out more about tree-ring dating, visit The Laboratory of Tree-Ring
Research at the University of Arizona. The site includes interactive
features that allow you to create your own skeleton plots.