The procedure of dating

The procedure of Dendrochronology rests upon the fact that there is a different increment in a trees growth depending on location-based influences. A major influence on a trees growth is climate. The thicknesses of annual rings often can even be visible to the unaided eye. The array of more or less large annual rings frequently results in a characteristic pattern which can be converted graphically to a curve shape with more or less distinctive amplitudes due to climatic influences in the course of the years.

If an average is made out of contemporary curves from trees of different locations within the same climatic region, a curve can be deduced in which the supra-local influences are emphasized and the individual or local influences are suppressed. 

This is the beginning of a tree ring curve (average curve) as a necessary tool for dating. Scientific research carried out by D. Eckstein (“Dendrochronologische Datierungen in Kirchendachwerken der Hellwegzone und Untersuchungen zur Datierbarkeit von weit- und engringigem Holz" in Westfälische Zeitschrift, Band 141/91.) has shown that the characteristic pattern of a region may be already distinct even with a coverage density of only 8 samples. A calendar which has been built in the 1970s, the so called “Weserbergland-oak chronology” consists of 519 single measurements for a period from 1004 to 1970 A.D., although with different coverage density. Recent research has lead to vast calendars with gapless sequences of up to 10.000 years.

Only the existence of such a calendar makes dating possible. Since the 1960s the network of chronologies existing for central Europe has become more and more dense. Today a dating of samples in this region should be possible, although dendrochronologically problematic areas are still remaining, as northern Germany and the Netherlands for instance, which were already mentioned in the chapter on sample quality.