To Study the Age and Lives of Trees

Trees growing in areas with clear variations between seasons form tree rings consisting of summer wood and autumn wood. Wider tree rings are formed during years with wet summers. Water means nutrients. Dry summers creates narrower tree rings. 

Several climate-related and environmental factors affect the growth of trees. In addition to precipitation, these conditions include light, wind exposure, snow depth or changes in nutrient supply when other individual trees are added or disappear.

Most trees of the same species within the same geographical location have similar series of wide and narrow tree rings. 

Dendrochronology is a method for studying forests over time with the aid of growth rings. The name comes from the Greek word "dendron" (tree), "chronos" (time) and "logia" (to learn).

Beginning with trees with a known reference year for the outermost growth ring, it is possible to gradually create a reference series that stretches back through time. Using of these references, it is possible to determine the age of other tree samples from the same area, for example dead wood where the outermost ring is not known. Each growth ring in a tree sample is registered by scanning and subsequent visual analysation in special computer programs; it can then be compared with measurement series from other trees.

Overlapping growth ring-series from trees that have lived during different time periods can be linked into continuous chronologies stretching several thousand years back in time. In this way, not only the age of individual trees can be determined; their growth rings can also supply information regarding changes in the forest environment over time.