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When one can match these tree-ring patterns across successive trees in the same locale, in overlapping fashion, chronologies can be built up—both for entire geographical regions and for sub-regions.Moreover, wood from ancient structures with known chronologies can be matched to the tree-ring data (a technique called cross-dating), and the age of the wood can thereby be determined precisely.Dendrochronologists originally carried out cross-dating by visual inspection; more recently, they have harnessed computers to do the task, applying statistical techniques to assess the matching.To eliminate individual variations in tree-ring growth, dendrochronologists take the smoothed average of the tree-ring widths of multiple tree-samples to build up a ring history, a process termed replication.In addition, particular tree-species may present "missing rings", and this influences the selection of trees for study of long time-spans.For instance, missing rings are rare in oak and elm trees.

The inner portion of a growth ring forms early in the growing season, when growth is comparatively rapid (hence the wood is less dense) and is known as "early wood" (or "spring wood", or "late-spring wood" Many trees in temperate zones produce one growth-ring each year, with the newest adjacent to the bark.A tree-ring history whose beginning- and end-dates are not known is called a floating chronology.It can be anchored by cross-matching a section against another chronology (tree-ring history) whose dates are known.Hence, for the entire period of a tree's life, a year-by-year record or ring pattern builds up that reflects the age of the tree and the climatic conditions in which the tree grew.Adequate moisture and a long growing season result in a wide ring, while a drought year may result in a very narrow one.

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