Dendrochronology is the study of tree-rings to determine when and where a tree has grown. Everybody knows that trees produce one ring every year. But the rings also vary in width according to each year’s local weather conditions. If you’ve got enough rings in a wood sample, then their widths form a unique “bar code”. Collect enough samples of various ages from buildings and bog wood, and you can join the bar codes up to a reference curve covering thousands of years.
Dendrochronology has a serious organisational problem that impedes its development as a scientific discipline and tends to compromise its results. This is the problem of proprietary data. When a person or organisation has made a reference curve, then in many cases they will not publish it. They will keep it as an in-house trade secret and offer their paid services as dendrochronologists. This means that dendrochronology becomes a black box into which customers stick samples, and out of which dates come, but only the owner of the black box can evaluate the process going on inside. This is of course a deeply unscientific state of things. And regardless of the scientific issue, I am one of those who feel that if dendro reference curves are produced with public funding, then they should be published on-line as a public resource.
But there is a resistance movement: amateur dendrochronologists such as my buddies TorbjÃ¶rn Axelson and Ã ke Larsson. They practice open source data transparency on the net, which means that arguably amateur dendrochronology is at this time more scientific than the professional variety. TorbjÃ¶rn recently published a fascinating study of a wooden building in Dalecarlia, showing that it was originally built in ~1240 and then refurbished in the 1490s, the 1570s and the 1830s. If you doubt his results, then just re-run the analyses. His data are all there in the report. I came into contact with TorbjÃ¶rn through Aard and then had the pleasure of seeing his 2007 debate piece into print in FornvÃ¤nnen, introducing many other professionals to the issue. (English translation here.)
Now the guys have started a wiki and dug into Alf BrÃ¥then’s work. Alf (born in 1924) is an old-school non-computerised dendrochronologist who hasn’t generally published his reference data. He once famously dropped nine years from his pine curve for Gotland, causing Johan RÃ¶nnby to unwittingly publish an erroneous date for the Bulverket lake settlement in his 1995 PhD thesis. TorbjÃ¶rn and Lars have re-analysed some data from VÃ¤stergÃ¶tland that Alf has released, and whaddaya know: there are errors there too.
The point here isn’t to say that Alf BrÃ¥then is an unusually clumsy dendrochronologist. He probably isn’t. The point is that all scientists are fallible, and that science moves forward through discussion. We help spot each other’s mistakes, and once an issue has been wrangled over and everybody’s had a chance to check the details, we have more secure knowledge than can ever be attained by a few people tending their black box. But as long as data and methods stay in that box, the process is impeded.
Update 24 June: Here’s something really scary. Says TorbjÃ¶rn,
The most problematic issue from an archaeological perspective may be that the Hohenheim data (Germany), which forms a lot of the basis for radiocarbon calibration, is not open to inspection. Nobody outside the “circle of the initiated” has seen the measurement series nor the average chronologies. We know that European dendrochronologists have often used the Gleichlaufigkeit method (GLK), which is not dependable, but which places great demands on the skill of the analyst. If you run GLK “blindly” you can end up anywhere. Anybody who says so in public, though, is likely to make few friends.