What is the origin of archeological oak timber? Researchers of three European labs were able to extract and analyze DNA from ancient wood (aDNA) to pinpoint the origin of oak wood from historic buildings and shipwrecks of even 700 years old. Identification of wood origin tells us about past human-environment interactions in the region as well as organization of timber trade networks.
Oak wood was highly appreciated and widely used for construction in past centuries. As population sizes expanded in some regions of Europe, local forests were depleted of high-quality timber. Therefore, regions of soaring economies were importing timber initially from the European market and eventually from other continents. Origin of archaeological and historical timber is usually identified by means of dendroprovenancing. This is matching of tree-ring-width series of timber of unknown origin with reference datasets. These datasets are available for many regions all over the world. But dendrochronological research is not always possible, for example because of a lack of sufficient rings due to the limited size of the wooden remains.
DNA for timber provenancing
DNA extracted from ancient wood can be used to identify the origin of timber on continental scale, but also to detect potential source areas within continents. For example oak timber from the Baltic area can be distinguished from timber of other regions within Europe based on reference DNA datasets. The challenge is to get a sufficient amount of genetic material from historic and archaeological timber. Especially since constructions are mainly built with heartwood - the dark wood that sits in the centre of the trunk. Heartwood contains many inhibiting substances that make it difficult to analyse DNA. In a collaborated effort three labs developed and compared two different methodological protocols for the extraction of DNA. Researchers were able to extract DNA in sufficient amounts and quality for genetic provenancing from sapwood and heartwood of living trees, historic buildings and - the most challenging - archeological shipwrecks.
Historic buildings and shipwrecks
The researchers used dendrochronologically dated timber from a 400-year old historic house in Horsens, Denmark, a 650-year old church door from Riga, Latvia, and a 700-year old Mönchgut Ostsee VII shipwreck from Northern Germany. In most cases the results of DNA analyses confirmed the results from tree-ring analyses. This indicates that DNA analyses is a promising tool to identify origin of ancient timber which cannot be provenanced by using tree rings. The relatively high success rate of aDNA extraction of 56% is promising for future studies and can likely even be enhanced by better sampling protocols. For a long time, maritime archaeology is seeking for a reliable timber provenancing method. With this study we made an imported step in this direction.