DENDROCHRONOLOGY is a method of dating timber by comparing its pattern of tree-rings with a master tree-ring chronology.
Every year a living tree puts on a new layer of growth under the bark. In years when conditions are favourable to growth, the width of the layer – the tree-ring – will be greater than when conditions are not as favourable. Trees living at the same time, in the same area, will exhibit similar patterns of growth. A master tree-ring chronology can be built up by overlapping the ring patterns of successively older timbers, starting with living trees and working backwards through historical samples. (Sheffield Dendrochronology Laboratory, for instance, has a continuous sequence for England going back to about 5000BC.) A sample of the timber to be dated is matched against the reference chronology. This will provide a date for each ring. If a bark edge is present in the sample, then the date of the outer ring will be the year the tree was felled. If the bark has been trimmed off, the felling date will be less precise, but it will still be more accurate than any other dating method.