Crannogs are substantial timber constructions. While there is some debate on exactly how crannogs were constructed, wood is the primary material used (although there are exceptions in some parts of Scotland). As Oakbank is one of the most extensively excavated crannogs in Scotland, it offers important insight into the wood that was used to build crannogs.
Crannog builders were quite particular about the tree species they used to build their habitations. This has implications for us as archaeologists (more on this in a future blog post!), but there is no doubt that crannog builders were master woodworkers and understood how and where to use different kinds of wood.
Alder (Alnus glutinosa) is by some margin the most common species of tree used as timber at Oakbank. This is paralleled at most other crannog sites in Scotland which have been excavated. Alder is somewhat peculiar in that it resists rot exceptionally well when completely waterlogged or submerged. This quality was surely known to crannog builders in the Iron Age. This, and its near ubiquity in Scottish forests, explains its prevalence at Oakbank and most other crannogs.
Oak (Quercus sp.) is the next most frequent species encountered. There is a particular concentration of oak used in the causeway structure at Oakbank. As most crannogs do not have causeways (or at least identified ones), the use of oak here may be unique to Oakbank. Oak is very strong while also very resistant to rotting, an important quality on a crannog constantly exposed to the wet.
The third most common species of tree used in constructing Oakbank crannog is hazel (Corylus avellana). While not used in major structural features, hazel is found most often in the internal space of the roundhouse. It is usually small, straight branches. These were coming, in all likelihood, from coppiced or managed copses of trees. Hazel is a very bendable wood and can be encourage to grow straight narrow poles useful in a range of applications from wattle for walls to weaving for basketry.
Elm, willow, and Scots pine are all also found from Oakbank, but in relatively small quantities. All of these species are commonly encountered around Loch Tay today (with the exception of elm due to Dutch elm disease). Knowing and working with timber must have been an essential and everyday part of living on water.