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DENDROCHRONOLOGYDendrochronology is a method used for studying tree-rings. The growth of trees often reflects annual variations in climate. Trees from the same species will thereby often have a matching pattern of annual tree-rings over large areas. In Norway the growth of conifers often correlates with the annual variation in summer temperature.
A warm summer normally provides a wider tree-ring than avarage, a cold summer a narrower tree-ring while an avarage summer has average growth. This will over a long period produce a tree-ring pattern unique for those years. A matching of the growth pattern from a sample with long tree-ring chronologies will thereby enable us to identify the actual period the tree was growing and thereby to perform a dendrochronological dating. If the number of tree-rings is sufficient and the outermost tree-ring is present in the sample, which can be seen if the bark is intact, dating of the felling year can be performed using dendrochronology.
The basis for dendrochronological activity is the construction of absolute tree-ring chronologies as far back in time as possible. Matching the tree-ring pattern from two samples from trees grown during the same period is called cross-matching. Matching the tre-ring pattern from a sample of unknown age to a tree-ring pattern related to calendar years performs a dating. By starting with living trees a long chronology back in time can be constructed by overlapping of successively older tree-ring series.
Before a house can be dated it is normal procedure to take samples from at least 10 different logs, and to construct a mean curve from the logs that contain a matching tree-ring pattern. This is necessary, as tree-ring growth is also sensitive to other environmental factors then climate.
As the tree-ring pattern matches the summer temperature, long tree-ring chronologies are known to contain valuable information on climate, thus giving rise to the sub-field of dendroclimatology, which studies climatic variations back in time.
Since tree-ring growth is also sensitive to many other environmental factors like pollution, geomorphological changes, river floods, etc. other sub-fields also exist, such as dendroecology, dendromorphology and dendrohydrology, which study the ecology of biotic communities, geomorphic processes and the history of flooding.