Dendrochronology and local history

Last update 1 Nov 2013.

What is Dendrochronology?

Dendrochronology is an exact method of dating wood.

Tree growth only occurs in the outer layer between the bark and the actual trunk. In temperated zones of the world, trees only grow during the warm period of the year. During the summer the growth is relatively fast resulting in a light wood. In the autumn the growth is slower and gives a dark wood. If the weather is warm with a lot of rain we get a wide ring of new wood that year. If the weather is cold or there is no rain for a long period the ring width of that year will be very narrow. This creates a pattern of individual tree rings of varying width depending on the current local climate, i.e. depending on the variations in precipitation and temperature.

The weather variation over a number of years gives a ring width growth pattern which is characteristic for those years. We could say that it looks like an individual fingerprint of that period.

By measuring tree growth over a long period, a reference curve can be constructed showing mean values of the differences in annual growth. The curve is constructed from tree samples of varying age where the period of growth for any sample overlaps the periods of growth for some other samples.

Usage. Today, dendrochronology is used around the world for identifying variations in local and world climate. It is also used for dating historical buildings and archeological findings of wood.

Local history

When people grow older they become more and more interested in history. They have seen things change successively or abruptly during their lives. This creates an emotional understanding that time and change is a dimension. May be this interest also comes from our striving to find a structure in everything. To understand an historical course of events is also to understand why things are as they are today.

Dendrochronology makes it possible to exactly date a number of events in an area around us. When was this house built? And as a resulting question, why did they build a new house there and then?

The remaining last things of a pier down in the water or successively getting out of the water because of elevation of the land. When was it used? When was it built? For what? Why was it left to corruption?

My own interest in dendrochronology also comes from a fascination over mother nature who has created her own yardstick - the tree rings - for the registration of years.

Why these pages?

Historical knowledge about our neighbourhood is a quality in our lives. Understanding why things are as they are. Dendrochronological dating methods can be a tool for amateur historians who want to understand local history.

Until now old houses in bad condition are at best photographed before they are demolished. Commercial dendrochronological dating is usually out of question because it costs too much money and it does not give any new outstanding knowledge. Though it may be a piece when understanding what actually happened.

These pages are partly meant to be something of a starting kit for historical amateurs who want to use this dating method on simple timbered houses and constructions in their neighbourhood. The CDendro program itself is also meant to be a tool for students who want to experiment with this statistical method for dating wood.

If you use this "starting kit" with its dating program CDendro, I do hope that you document and publish what you have done together with your measurements and perhaps also with your scanned images. Only by making it possible for others to reproduce our datings can we expect them to be taken seriously. We also need to share our information to facilitate our research.

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