Estimer le diamètre des bois carbonisés à partir de l'observation de la courbure des cernes de croissance des charbons de bois archéologiques : nouvelle contribution méthodologique Estimating the diameter of charred wood from the observation of the curvature of the tree rings of archaeological charcoal: a new methodological contribution

Recent developments of anthracology to better understand past woodland management and wood collection strategies, allow telling how landscape changed over centuries. Among these developments, a key role is occupied by the estimation of round wood diameter based on the analysis of charcoal remains. This approach, originally based on the qualitative observation of tree-ring curves, is now based on image analysismeasurement of ring-curvature. However, only a few anthracological studies are nowadays profiting from this technique, especially in rescue archaeology. In fact, round wood diameter estimation still requires expensive tools (e.g. digital cameras and programs for image analysis) and is quite time-consuming. Here I suggest an adapted qualitative model based on the observation of the three ring-curvature classes (curved, intermediate and straight) by defining their limit values. The first step of the model is based on the systematic study of tree-ring curves in observation windows with 10 and 5 mm sides on a perfect target and six cross sections of aged coppice oak (Quercus robur L.) and chestnut(Castanea sativa Mill.). This phase brings us to the estimation of the maximum curvature ray (in mm) for charcoal samples with curved tree-rings and for those with intermediate.rings. The second step consists in making a number of tests on the limit values obtainedby using an anthracological corpus well known: three experimental charcoal kilns for whichthe diameter of the wood samples contained had been made measuring before thecarbonization process occurred. To conclude, the limit values of the three classesmentioned have been confirmed and can be used for future anthracological analyses Les récents développements de l'anthracologie visent à renseigner les modes de collecte du bois, les pratiques sylvicoles et la physionomie évolutive des peuplements forestiers. Parmi ces développements, l'estimation du diamètre initial des bois carbonisés à partir de l'étude des charbons résiduels occupe une place centrale. Cette approche, initialement fondée sur l'observation de la courbure des cernes, s'appuie aujourd'hui sur la mesure précise du rayon de courbure (aussi appelé distance à la moelle) à l'aide de logiciels d'analyse d'images. Pourtant, force est de constater qu'encore trop peu d'études anthracologiques mobilisent cette approche, en particulier dans le milieu de l'archéologie préventive. Les raisons invoquées sont doubles : les équipements nécessaires (caméra et