Crossdating by skeleton plotting
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The ring widths are inspected with a magnifying glass and vertical lines of various height are drawn for those lines which are narrow.Especially wide rings are marked with a "b" (broad). If you draw your plots on strips of graph paper, these strips can be horizontally shifted relative to each other so you can find where the plots match each other.
This is probably the most fundamental and important aspect of tree ring research.
There is also a "Skeleton Curve" available in CDendro.
The Uniformitarian Principle The Principle of Limiting Factors The Principle of Aggregate Tree Growth The Principle of Ecological Amplitude The Principle of Site Selection The Principle of Crossdating The Principle of Replication Please consult the Primer on Statistics to refresh yourself on the basic principles of correlation and regression that may be used to analyze tree growth patterns and the relationship of climatic variables to annual growth.
Examples of results are presented for specimens from sensitive, moderate, and complacent sites.
FORTRAN program listings are included for two subroutines for (a) identifying small rings and (b) producing the plot.
What the skeleton plot does is to extract the most pertinent information and record it on a graph.
In pre-computer times dendrochronologists had to rely on techniques which are not calculation intensive, but instead made the most of the human capacity of pattern recognition. Each vertical line on the graph paper correponds to one ring of the sample.Here, the curve is shown detrended (and somewhat zoomed out) to make the calculations behind the skeleton lines more obvious.(The slider (trackbar) of the "Settings/Plotting window settings/Set relative height of ring width curves" has also been somewhat adjusted to make the ring width curve higher.) When there is a reference available, this is plotted as a blue upside-down skeleton plot.For a comparison of rings from tree to tree, the pattern of thin versus wide rings must be recorded on a standard graph. Skeleton plots show tree growth in years that stand apart from other years, because the tree experienced either greater than average or less than average growth.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.