WOOD CHARCOAL : INTRODUCTION
About wood charcoal
Wood charcoal is the result of incomplete combustion of wood, due to an inadequate supply of oxygen. The combustion process can be broken down into four stages, each one corresponding to different temperatures: dehydration (< 200°C), char formation (200-280°C); carbonisation (also called pyrolisis) (280-500°C) and ignition (> 500°C). Shortage of oxygen prevents completion of combustion process, i.e. ignition doesn't happen and wood doesn't turn into ash. As its name suggests, wood charcoal are formed during the carbonisation stage and are not preserved if temperature reaches more than 500°C. As the result of incomplete combustion of wood, wood charcoal are remains of different parts of ligneous plants (trunk, branch, twig, stem, root). However roots identification is not concerned by this part of the tutorial, as already covered in another part of it (see Charred roots and tubers).
Archaeological records of wood charcoal
Wood charcoal formation occurs as the result of a fire, controlled or uncontrolled. On archaeological sites, wood charcoals are the remains of firewood or construction wood (timber wood, or objects and tools made of wood) mixed through the sediment or preserved in situ with others archaeological structures. Thus they provide information about human practices in the past, regarding ligneous plants uses and supply strategies.
In the following sections, we're using indifferently the terms anthracology and wood charcoals analysis. The IVth International Meeting of Anthracology, held in September 2008 in Brussels, Belgium, has shown some dissenssions about the use of anthracology as a general meaning of wood charcoals analysis. Here, we assumed that anthracology is corresponding to the study of wood charcoals on archaeological sites (otherwise called archaeo-anthracology).
Short history of anthracology
The first identifications of archaeological wood charcoal go back to the end of the XIXth century, on sites in Switzerland and Germany (Heer 1866, Prejawa 1896). At first the samples retrieved were very limited, being wood charcoals associated with hearths. Furthermore identifications were achieved with a transmitted light microscope, which involves mounting charcoal on a slide, a long and tedious process. Results thus obtained were simply presented as lists of species and were more interesting from an ethnobotanical point of view than from an ecological one.
Use of reflected light microscopy gave rise to a true revolution in wood charcoal analysis techniques. From that moment onward, charcoal could be identified without a tedious preparation, simply by breaking them (Western 1973). Using this type of microscope saved a huge amount of time, so a much larger number of fragments could be identified and analysed. In addition ecological studies could be achieved, which increased the range of information such archaeological remains could provide. Thereafter anthracological studies experienced a true development, which is summarized in various publications (e.g. Heinz 1990, Chabal 1992) and websites (e.g. Eleni Asouti website). A recent lecture given by Stéphanie Thiébault in the IVth International Meeting of Anthracology (8th-13th September 2008) has given an updated state of the development of anthracology.
Methods and themes in anthracology
Different methods are used in anthracological studies, allowing vegetation and climate reconstruction or study of wood economy (sometimes both). Below are short descriptions of three of these methods, all connected to economical studies. In the box on the right are comments about how vegetation and climate history could be referenced by anthracology.
Identification and analysis of taxa
This is the main method used in anthracology. It consists in analysing taxa determined and how they relate with each other. Its purpose is to reconstruct vegetation history and its exploitation, either on a regional (Heinz et al. 1993, Chabal 1997, Willcox 2002, Tengberg 2005) or a local scale (Miller 1985, Badal Garcia 1992, Asouti and Hather 2001, Marinova and Thiébault 2008). This method can also provide some evidences about selection and exploitation of particular species, by showing 'weird behaviour' in wood charcoal assemblages (Thiébault 2005).
Work of identification can be completed by a dendrological study applied to wood charcoal. In addition to the basic identification process, some features are also noted, like growth ring curvatures and width, presence of bark, of pith, and so on (Marguerie and Hunot 2007). Some studies focus on the reconstruction of diameter of wood burnt (Dufraisse 2008, Ludemann 2008), while others are interested in anatomical features observed in the rings due to pollarding or copicing of certain species (Thiébault 2006). All the information acquired with this type of study provide evidences about woodland management and wood supply areas (wood supply strategies in an overall perspective).
Closed to dendro-anthracology, quantitative eco-anatomy is the statistical analysis of the diameter and the distribution of vessels in the early and late wood. This method is applied to differentiate two species of a same genus when microscopic observation doesn't allow such an accurate determination. Up till now it has succeeded in distinguishing domesticate from wild olive and grape, thus providing information on fruit trees cultivation (development, irrigation practice...) in the Western Mediterranean area (Terral 2000, Terral 2002).
Others themes related to anthracology
Dendrology can also be applied to anthracology with the aim of dating site occupation and reconstructing past climate (see Salisbury and Jane 1940 for one of the first work on this matter; for more recent work refer to Kuniholm et al. 2005, Newton et al. 2005, Griggs et al. in press). Also, quantitative eco-anatomy analysis can provide information about climate (in particular about wild olive growing under different climatic conditions) (Terral and Mengüal 1999, Heinz et al. 2004).
Finally isotope analysis was applied recently on wood charcoal, aiming on the reconstruction of rainfall by measuring amount of 13C in wood charcoal (Ferrio et al. 2006, Fiorentino et al. 2008).
- Asouti, E., Hather, J. (2001). Charcoal analysis and the reconstruction of ancient woodland vegetation in the Konya Basin, south-central Anatolia, Turkey: results from the Neolithic site of Catalhoyuk East. Vegetation History and Archaeobotany 10:23-32.
- Badal Garcia, E. (1992). L'anthracologie préhistorique : à propos de certains problèmes méthodologiques. Bulletin de la société botanique de France. Actualités botaniques 139 (2/3/4): 167-89.
- Chabal, L. (1992). La représentativité paléoécologique des charbons de bois archéologiques issus du bois de feu. Bulletin de la société botanique de France. Actualités botaniques 139 (2/3/4): 213-236.
- Chabal, L. (1997). Forêts et sociétés en Languedoc (Néolithique final, Antiquité tardive) : l'anthracologie, méthode et paléoécologie. Documents d'Archéologie Française 63.
- Dufraisse, A. (2008). Firewood management and woodland exploitation during the late Neolithic at Lac de Chalain (Jura, France). Vegetation History and Archaeobotany 17:199-210.
- Ferrio, J.P., Alonso, N., Lopez, J.B., Araus, J.L., Voltas, J. (2006). Carbon isotope composition of fossil charcoal reveals aridity changes in the NW Mediterranean Basin. Global Change Biology 12: 1253-1266.
- Fiorentino, G., Caracuta, V., Calcagnile, L., D'Elia, M., Matthiae, P., Mavelli, F., Quarta, G. (2008). Third millennium BC climate change in Syria highlighted by Carbon stable isotope analysis of 14C-AMS dated plant remains from Ebla. Palaeogeography, Palaeoclimatology, Palaeogeography 266: 51-58.
- Griggs, C.B., DeGaetano, A., Kuniholm, P.I., Newton, M.W. (in press). A regional high-frequency reconstruction of May-June precipitation in the north Aegean from oak tree rings, A.D. 1089-1989. International Journal of Climatology.
- Heer, O. (1866). Planfzen der Pfanhlaubten. Neujbl. naturf. Ges. Zürich aus das Jahr 1866: 1-54.
- Heinz, C. (1990). Dynamique des végétations holocènes en Méditerranée nord-occidentale d'après l'anthracoanalyse de sites préhistoriques : méthodologie et paléoécologie. Montpellier: Paléobiologie continentale, XVI/2.
- Heinz, C., Vernet, J.-L., Thiébault, S. (1993).Gestion et dégradation de la forêt préhistorique méditerranéenne. Actes du XVIe colloque interrégional sur le Néolithique. Documents d’Archéologie Française 39. Éd. de la MSH, Paris : 12-18.
- Heinz, C., Figueiral, I., Terral, J.-F., Claustre, F. (2004). Holocene vegetation changes in the northwestern Mediterranean : new palaeoecological data from charcoal analysis and quantitative eco-anatomy. The Holocene 14(4): 621-627.
- Kuniholm, P.I., Newton, M.W., Griggs, C.B., Sullivan, P.J. (2005). Dendrochronological Dating in Anatolia: The Second Millenium BC. Der Anschnitt, Anatolian Metal III, Beiheft 18: 41-47.
- Ludemann, T. (2008). Experimental charcoal-burning with special regard to anthracological wood diameter analysis. Pp. xx-xx, in Charcoals From the Past: Cultural and Palaeoenvironmental Implications Proceedings of the Third International Meeting of Anthracology, Cavallino - Lecce (Italy) June 28th - July 1st 2004, eds. G. Fiorentino and D. Magri. BAR International Series 1807.
- Maguerie, D., Hunot, J.-Y. (2007). Charcoal analysis and dendrology: data from archaeological sites in north-western France. Journal of Archaeological Science 34: 1417-1433.
- Marinova, E., Thiébault, S. (2008). Anthracological analysis from Kovacevo, southwest Bulgaria: woodland vegetation and its use during the earliest stages of the European Neolithic. Vegetation History and Archaeobotany 17: 223-231.
- Miller, N.F. (1985). Paleoethnobotanical Evidence for Deforestation in Ancient Iran : a case study of urban Malyan. Journal of Ethnobiology 5/1: 1-19.
- Newton, M.W., Wardle, K.A., Kuniholm, P.I. (2005). Dendrochronology and Radiocarbon Determinations from Assiros and the Beginning of the Greek Iron Age. Proceedings of the Conference of Archaeological Research in Macedonia & Thrace, held in Thessaloniki, 2003: 173-190.
- Prejawa, H. (1896). Die Ergebnisse der Bohlweguntersuchungen im Grenzmoor zwischen Oldenburd und Preussen und in Mellinghausen im Kreise Sulingen. Mitt. Ver. Gesch. Landeskde 21: 98-178.
- Salisbury, K. J., Jane, F.W. (1940). Charcoals from Maiden Castle and their significance in relation to the vegetation and climatic conditions in prehistoric times. Journal of Ecology 28: 310-325.
- Tengberg, M. (2005). Les forêts de la mer. : exploitation et évolution des mangroves en Arabie Orientale du Néolithique à l'époque Islamique. Paléorient 31/1: 39-45.
- Terral, J.-F. (2000). Exploitation and management of the olive tree during Prehistoric times in Mediterranean France and Spain. Journal of Archaeological Sciences 27 (2): 127-133.
- Terral, J.-F. (2002). Quantitative anatomical criteria for discriminating wild grape vine (Vitis vinifera ssp. sylvestris) from cultivated vines (Vitis vinifera ssp. vinifera). Pp. 59-64, in Charcoal Analysis. Methodological Approaches, Palaeoecological Results and Wood Uses. Proceedings of the Second International Meeting of Anthracology, Paris, September 2000, éd. S. Thiébault. BAR International Series 1063.
- Terral, J.-F., Mengüal, X. (1999). Reconstruction of Holocene climate in Southern France and Eastern Spain using quantitative anatomy of olive wood and archaeological charcoal. Palaeogeography, Palaeoclimatology, Palaeoecology 153: 71-92.
- Thiébault, S. (2005). L’apport du fourrage d’arbre dans l’élevage depuis le Néolithique. Anthropozoologica 40(1): 95-108.
- Thiébault, S. (2006). Wood-anatomical evidence of pollarding in ring porous species: A study to develop? Pp. 95-102, in Charcoal Analysis: New Analytical Tools and Methods for Archaeology. Papers from the Table-Ronde held in Basel 2004, ed. A. Dufraisse. BAR International Series 1483.
- Thiébault, S. (2008). Archaeological charcoal records: Experience and perspectives. Keynote lecture, IVth International Meeting of Anthracology, 8th-13th September 2008, Brussels.
- Western, C.A. (1973). The Ecological Interpretation of Ancient Charcoals from Jericho. Levant 3: 31-40.
- Willcox, G.H. (2002). Evidence for ancient forest cover and deforestation from charcoal analysis of ten archaeological sites on the Euphrates. Pp. 141-145, in Charcoal Analysis. Methodological Approaches, Palaeoecological Results and Wood Uses. Proceedings of the Second International Meeting of Anthracology, Paris, September 2000, éd. S. Thiébault. BAR International Series 1063.