Dendrochronology is the dating of artefacts through the use of tree rings, and was originally pioneered by A. Douglass, for astronomical research (Michels 1973: 115-6). The principle behind dendro-dating is that trees add an extra ring of growth to their trunk for each year they are alive. The width of this ring is dependent on the suitability of the year for growth. A good year will produce a thick ring, a poor year will produce little growth, or may even leave traces of frost damage.
The beauty of the technique is that trees have relatively little personal opinion on the weather, and so all trees of the same species within the same region will exhibit similar patterns. If the sequence of patterns of similar for live trees, it can be assumed that dead trees operated under the same conditions. By examining the rings in dead trees, the date of the death of the tree can be measure with reference to the live trees. Trees that died further back in time can be dated
with respect dead trees of known era and so on. The data collected can have a number of uses.
Douglass was interested in past climate, as his research was concerned with solar activity. Current work in this field is being done by dendrochronologists, such as Mike Baillie of Queen’s University. The examination of tree rings from across the globe point to a climatic downturn, which may have had profound implications for past populations and social order. However the work is controversial. Current explanations of the climate change lack elegance, and may lay too heavy an emphasis on environmental determinism.
More widely accepted is the use of dendrochronology for the dating of past artefacts and contexts. The limitations of the method are that the tree rings need to be visible, and so the primary use in Europe is dating of structures, such as houses. Houses are datable as there is a tradition of timber built houses in Europe. By examining the dates of the beams, the date of the associated house can be inferred. If logs were re-used in building the dates obtained may not carry the full story of occupation (Pryor 1991: 111).
The key problem for dendra-dating is that there are so many artefacts that have not been fashioned out of logs. However the high accuracy of dendro-dating has had massive implications. An example of where dendro-dating has been used successfully is at the site of Flag Fen.
Flag Fen is a waterlogged site just east of Peterborough. The waterlogging has left much of the wood protected from oxygen, and has therefore inhibited the rotting process. As a result enough logs were found to allow the site to be dated. The chances of logs matching a master chronology by chance were dealt with by stipulating that the logs should hold at least sixty rings. The study of the logs from across the site established an occupation from 1363 to 967 BC. Crucially the logs were all of roughly the same age, indicating that the site had been one construction (Fagan 1995:137-8), which will have massive ramifications for any models of construction of the site. However for many archaeologists, working in less waterlogged conditions, the most important use of dendrochronology is as a check on other forms of dating, radiocarbon being the most famous case (See Renfrew 1973 Ch4).
