Saturday, November 25, 2017

Dendrochronology

Dendrochronology is literally “tree dating” and is a scientific way of dating accurately the timbers which survive in old houses or other archaeological sites. Each year trees produce a growth ring, and these vary in thickness depending on weather conditions (and other factors), so over time a sequence of tree rings builds up. Dendrochronology works backwards from surviving trees and from timbers in old buildings such as churches or timber-frame houses, and from timbers on excavated sites, and has built up a master chronology.

Timbers from other sites or buildings have a small “core” drilled out of them containing a section of all the available tree rings, and this is compared with the known chronology, enabling a date range to be identified. If the outer (bark) ring or next inner rings (sapwood) are present, then a very accurate date can be suggested for when the tree was felled; and as most wood in past times seems to have been worked when “green”, this will be close to the date of use of the timber, perhaps in the construction of a large house.

At present a complete sequence is only available for oak, so it can be disappointing to find (as we have done during the project) that a building we had hoped to get dated in this way is constructed of elm, which can’t yet be dendro-dated.

So far we have had timbers from one building dated in this way, and will be doing more of this work in the future. Frequently we can compare the dating results from dendrochronology and a building survey with documentary evidence to find out a lot more about the building.

Old Astwood

This property has been given a “dendro” date of 1584

Dendrochronology © Dodderhill Parish Survey Project

This picture shows a small core being removed from a suitable timber, which may then be dated by matching tree rings on a previously dated sample.

National Lottery - Heritage Lottery Fund© Dodderhill Parish Survey Project 2007 | Site Design & Build: Red Box Consultants Ltd.