Dendrochronology is a scientific dating method that determines the exact year — and sometimes the season — when a tree was felled, by analysing the pattern of tree rings in its wood. It is among the most accurate dating techniques used in building archaeology.
How it works
Each year a tree adds a new growth ring to its trunk. The width of that ring reflects the growing conditions of that year: temperature, rainfall and soil nutrients all leave their own “signature”. Trees in the same climatic region show comparable patterns of wide and narrow rings.
The investigation runs in four steps:
- Sampling — a core or slice is taken from the timber
- Measurement — the width of every ring is measured under a microscope to within a hundredth of a millimetre
- Comparison — the measured sequence is compared with a reference chronology for the species and region
- Dating — if the statistical correlation is high enough, the exact ring sequence — and therefore the felling year — is established
What dendrochronology can and cannot do
Can:
- Date a beam or plank to the exact year of felling
- Identify the season (summer or winter) if the outer, incomplete ring is preserved
- Suggest the timber’s region of origin from the matching chronology
- Distinguish reused timber from material original to a given phase
Cannot:
- Give the exact age of a building if the outer rings are missing (only a *terminus post quem*)
- Date timbers for which no local reference chronology yet exists
- Date very young timbers (fewer than about 50 rings)
Use in building archaeology
Dendrochronology is mainly used for:
- Listed buildings — dating roof structures, floor beams, anchor beams and timber facades
- Restoration projects — distinguishing original from replacement timber
- Archaeology — dating timber piles, shipwrecks and wells
- Panel paintings — dating the oak panels of, for instance, Flemish masters
Limitations
For native European oak (Quercus robur) there is a continuous reference chronology back into prehistory. For imported timber (Baltic oak, Scandinavian pine) a foreign chronology has to be used. Softwoods and very young timber are often harder to date.
Related terms
- Tree ring
- Radiocarbon (C14) dating
- Building archaeology
- Wood
- Restoration
- Timber species
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