Dendrochronology is the formal term for tree-ring dating, the science that uses the growth rings of trees as a detailed record of climatic change in a region, as well as a way to approximate the date of construction for wooden objects of many types. As archaeological dating techniques go, dendrochronology is extremely precise: if the growth rings in a wooden object are preserved and can be tied into an existing chronology, researchers can determine the precise calendar year—and often season—the tree was cut down to make it. Radiocarbon dates which have been calibrated by comparison to dendrochronological records are designated by abbreviations such as cal BP, or calibrated years before the present. Tree-ring dating works because a tree grows larger—not just height but gains girth—in measurable rings each year in its lifetime. The rings are the cambium layer, a ring of cells that lies between the wood and bark and from which new bark and wood cells originate; each year a new cambium is created leaving the previous one in place.
Dendrochronology - Tree Ring Records of Climate Change
Dendrochronology: How Tree-Ring Dating Reveals Human Roots
Dating of archaeological timbers. Dating of period buildings. Dendrochronology or tree-ring dating is the scientific method of dating using the annual nature of tree growth in suitable tree species.
Dendrochronology tree-ring dating is now an established science in Britain. Progress has been rapid over the last 30 years or so, and most parts of the country now have well-replicated oak chronologies against which to date oak timbers. Some parts of the country are more difficult than others, for example in East Anglia the oaks have in the past grown to sizes suitable for large structural timbers in years, whereas a similar sized timber in, say Worcestershire, might contain rings. This is important because the patterns of varying ring-widths need to be firmly matched against the reference material in order to be sure of establishing the date.