Oak wood is the main raw material used for the building of the San Juan; at least two hundred oak trees are needed. About half of them have to be straight and the other half crooked. Nowadays oaks with straight trunks can be employed as beams for house building and furniture making, but crooked ones are only wanted for domestic firewood. It seems weird, if we consider that crooked oak trees have been highly valued until the end of wooden shipbuilding, since their tortuous shapes were essential for making good ship timbers.
Selection of trees
The oak trees for the San Juan come from the forests of the Sakana region, in the northwest of Navarre. All of them belong to one of three species of the Quercus genus: Quercus robur, Quercus petraea, and Quercus pubescens.
The selection of the trees has been carried out under the supervision of the forest wardens of the Navarran government and of each of the municipalities involved. Their professionalism and their know-how have been very helpful during the long days in the forests.
Straight oak trees typically have a long trunk and few branches; we will use them to make planks, beams, and other long, straight pieces.
Crooked ones, on the other hand, are essential to make structural timbers such as futtocks, floor timbers, knees, and so on. The grain of the wood has to follow the shape of the timber so it can bear huge stresses without breaking. We have to go to the forest with our templates and look for the crooked trees we need. It's not an easy task, as we need quite big timbers of very specific shapes.
When we find an oak tree with the right shape, and if the forest wardens agree, they mark the tree on its foot by punching it with a seal on the back of their special axe. A paint mark is done as well so it will be easier to spot it when we come back. A rough calculation of the volume of wood the tree will yield is also made.
Felling the oak trees
We chose the dates for cutting down the trees according to the Basque forestry tradition: in winter, during the waning moon, when its orbit is low over the horizon. When the season comes, the oak trees are felled. Care must be taken at this stage because a good oak tree can be irreparably damaged if it's cut down in a careless way.
Even so, not all the oak trees felled are useful. Many crooked trees that look splendid in the forest are hollow and rotting inside. It's only after cutting them down that the internal damage becomes apparent.
More pictures of building process here