Methods of dating trees
American Astronomre A E Douglass, who had a strong interest in studying the climate, developed the method around 1900 (4).
He theorised that tree rings could be used as proxy data to extend climate study back further than had previously been permissible.
Most importantly, assuming there are no gaps in the record (and even if there are short gaps), it can tell us the precise year that a certain tree ring grew (4).
The potential then, even with these two simple sets of data that we may extrapolate from the tree ring data, is enormous.
From the 1980s, several seminal studies began at the University of Arizona (6), (7) studying the bristlecone pine of California and hohenheim oak in Germany.
Thanks to the work of these studies, we now have an 8,600 year chronology for the bristlecone pine and in the region of 12,500 year chronology for the oak.
They are used for decoration in parks and gardens all over the world.
Some trees are also better than others for study (5). In this article we make the assumption that growth is annual with a distinct growing season.
Most tree species are reliable; oak is the most reliable tree type for tree rings - with not a single known case of a missing annual growth ring.
This enormous and comprehensive data set is fundamental to both European and North American studies of the palaeoclimate and prehistory (8).
There is one major drawback to dendrochronology and that is that we can only date the rings in the tree.