Dendrochronology

Dendrochronology is the method of scientific dating based on the analysis of tree ring patterns. Trees develop yearly tree rings of different thickness depending on weather, rain, temperature, etc. in different years. Trees from the same region will tend to develop the same patterns of width for a given period.

Laboratory analysis of timber core samples measures the width of annual rings. By taking samples from different sites and different strata within a particular region, researchers can build a comprehensive historical sequence that becomes a part of the scientific record; for example, ancient timbers found in buildings can be dated to give an indication of when the source tree was alive and growing, setting an upper limit on the age of the wood. Some trees are more suitable than others for this type of analysis.

A benefit of dendrochronology is that it makes available specimens of once-living material accurately dated to a specific year to be used as a calibration and check of radiocarbon dating. The bristlecone pine, being exceptionally long-lived and slow growing, has been used for this purpose, with still-living and dead specimens providing tree ring patterns going back thousands of years. For dating purposes, in some regions sequences of more than 10,000 years are available.

The dendrochronologist faces many obstacles, however, not least species of ant which inhabit trees and extend their galleries into the wood, thus destroying ring structure.