Tree ring dating and archaeology
It is also important to have enough rings to actually confirm a date.Once the rings are dates, the chronology is measured.Crossdating, the skill of finding matching ring-width patterns between tree-ring samples, is used to assign the precise calendar year to every ring.This is affected by the climate that the timber was in.The last step is to compare the rings with that of ring-width patterns in sampled timbers and a master dating chronology.For trees to be useful in archaeological analysis, they must "produce annual growth rings that are uniform around the tree stem", they must "live for decades and, preferably, centuries" and they "must have been used extensively by humans either for habitation or fuel." One of the problems with this evaluation is that it is possible under certain conditions for a tree to miss a growth-ring or produce two growth rings in a season.Once aligned, knowing the precise calendar year of any individual tree-ring is the same as knowing the calendar year of all the rings.The goal of a dendroarchaeologist is to determine the year when the last ring was formed.
Another difficulty in the use of tree-ring dating as applied to archaeology is the variety and condition of wood used in construction of archaeological sites. Heartwood can normally retain much of its substance and can be dried out and polished for analysis.
Patterns of tree growth will be similar between trees of the same species, growing in the same climate.
These matching patterns align growth rings in different trees formed in the same year.
Even if a reference chronology is available, care must be taken to identify aberrations in the ring pattern to determine if the sample is usable for dating.
Dendroarchaeology has been used extensively in the dating of historical buildings.