Dendroprovenancing shipwreck timbers: on overlaps and pizzas…

By Peter Groenendijk

The ultimate goal of the “Wood Sciences” work package within the ForSEAdiscovery project is the dendroprovenancing of the wood that was used in the construction of Iberian ships during the European Age of Discovery. In other words, we will attempt to discover the origin (the provenance) of this wood (dendron = wood, in Greek).

Why study this wood? Back then, wood was the basic building material for what was a high-tech industry that built vessels to cross into the unknown. At the same time, wood was a most valuable resource. First of all, because there were several competing seafaring empires, but also because wood was used as a construction material for houses, churches, and other buildings; people cooked with wood; wood charcoal was used to smelt iron; etc. Thus, studying how wood was used and traded back then provides us a window to peek into the past and understand how a key – and limited! – resource was exploited in the times that our globalised world was forged.

The single question “where did that wood come from?” thus underlies a complex mixture of the necessities of empires, their competition, and the dynamics of supply-and-demand chains that drove international trade networks. Assessing such complex matters requires complex approaches, hence the multi-layered multidisciplinarity of the ForSEAdiscovery project (History, Nautical Archaeology, and Wood Science). Dendroprovenancing is just one of these layers, and is by itself already quite multidisciplinary indeed!

Piecing it together

Reconstructing the provenance of a timber is something like trying to build a large, multi-layered puzzle of which we only have some of the pieces. Additionally, the image we are trying to reconstruct – the bigger picture! – is not entirely clear. In fact, it´s rather blurry! Piecing together this puzzle will not be an easy task to start with, but with the right pieces, laid in the right places, we should be able to get a glimpse of this bigger picture.

My focus for now will not be on this blurred bigger picture. Instead, I will try to explain our attempt to integrate the different methods we use – the pieces of the puzzle – to decipher the provenance of our “Woodie Goodies”. Integrating the results from the different methods boils down to finding the overlapping provenances provided by these methods and is perhaps best visualized as a metaphoric multi-layered pizza. More specifically, we are looking for that intersection between the tomato slice and the basil leaf, on the upper-right quarter of a quattro stagione pizza… I´ll try to elaborate this ramble!

The methodology

Basically, we will integrate the results of four different methods that provide us with data on possible provenances of the wood (so possible locations of wood origin). These methods cover different scales, both within the wood as well as spatially. Within wood, we will work in four levels, with things we can see and things we cannot. The work ranges from:

  1. the macroscopic level of tree-ring analysis (the growth patterns of the individual trees);
  2. passing through the anatomy of the wood at cell level (the year-to-year variation in size of water-conducting vessels in the wood);
  3. into the organic chemistry at molecule level (with analyses of DNA, and of the bio- and geochemical composition of wood);
  4. arriving at the atomic level using strontium isotope analysis.

I´ve tried to illustrate these different levels in the figure below (with corresponding numbers).

Dendroprovenancing

Concomitant signals

For each of these analysis levels, we need to analyse the wood of living trees to build the references with which the wood of shipwrecks can be compared. If we find a “signal” in the shipwreck wood that matches the signal of the trees from a known location, the shipwreck wood probably originated from that same location. Let´s take the information we can get from the analysis of tree rings as an example. By measuring the width of the rings, we can reconstruct how a tree grew during its life (sometimes over 500 years!). Years of “bad” growth (a narrow ring) often reflect a year with “bad” weather for the trees: here in Spain, for example, these are often dry and hot years. Years that are bad for one tree are often also bad for its neighbours, and trees from a certain region usually show a synchronized year-to-year variation in growth. This variation in the tree-ring widths of a set of trees reflects the climatic conditions of a region. As different regions have different climates, the patterns of variation in the tree rings can be used to identify where a tree came from: trees growing in southern Spain show a different pattern than trees growing in northern Spain (or in central Germany for that matter).

If we go back to our quattro stagione pizza, tree rings could thus provide us with information in the likes of which of the four quarters of the pizza (the stagiones) the wood came from: for instance, the wood could be from the upper-right quarter of the pizza,  you know, the “summer” quarter with the cheese, tomatoes and fresh basil!

Analysing the year-to-year variation in wood anatomy can be used to get similar spatial information as from tree-ring analyses. By measuring, for example, the area of water-conducting vessels in each growth year, we can also try to determine the provenance of the wood. However, the signal registered by the area of vessels differs from that registered in the tree-ring widths, as these two features of wood are formed during different parts of the year, and thus under different climatic signals. Vessels are formed in the very beginning of the growing season (they form the pipework that brings water to the newly formed leaves), whereas the remaining wood (and thus the ring-width) is formed later in the year. Since the variation in vessel sizes contains a different climatic signal than the tree rings, analysing both allows us to refine the area of possible provenance: the wood comes from the upper-right quarter of the pizza AND only from the areas covered with cheese!

Add the last ingredients

By overlapping the information from the other methods, we can increasingly include (or exclude) different areas. Organic chemistry may, for instance, tell us the trees were growing on a typical “tomato” area, while the strontium analysis may reveal a very strong “basil” signal in the wood… With that – and with a bit of luck! – we might thus be able to tell in the end, that the wood came from that intersection between the tomato slice and the basil leaf, on the cheese-covered upper quarter of my Iberian quattro stagione pizza**!

See my attempt to illustrate it below:

Iberipizza

 

The nice thing is that this area coincides with the Cuenca mountains north-east of Madrid. This area is known to have produced a lot of wood in the past and is also the place where the Tagus River originates. This river then flows west to Lisbon in Portugal, which was an important shipbuilding city!

Presto!!

This could just be that piece of the puzzle that might start to give us a glimpse of the bigger picture!

 


** I apologise for my poor image editing capabilities, but most of all, to any Italian reading this post!


Peter Groenendijk is one of the three Experienced Researchers in the ForSEAdiscovery project and is based at the Lugo Campus of the University of Santiago de Compostela. He works on the integration of the different methods used to determine the origin of timbers used in Iberian shipbuilding.

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