Charcoal analysis - A short history
It was in 1864, that the idea was conceived for the first time to analyse prehistoric wood charcoal macro-remains by the Italian G. Passerini and, following him, the Swiss O. Heer, in the context of the then recent impressive discoveries of the Neolithic and Bronze Age lake dwellings in Switzerland. At the beginning of the 20th century, the French clergyman and prehistorian Henri Breuil (1,2,3,) was the first to take an active interest in the study of wood charcoals recovered from Palaeolithic sites in France. At these very early stages, only material deriving from prehistoric hearth structures was destined for analysis and the interpretations sought by the researchers were of limited palaeoecological interest. Instead, the focus was on the choice of combustibles by the prehistoric groups.
The first explicitly ecological interpretations based on charcoal evidence appeared in Britain with the publication in 1940 by E. J. Salisbury and F. W. Jane of their report on wood charcoals from the Maiden Castle (1) excavations in Dorset (Salisbury and Jane 1940). In this paper, Salisbury and Jane suggested that the observed frequencies of individual taxa might correspond to their actual proportions in prehistoric woodland vegetation. They also used tree-ring data in an attempt to reconstruct past climate patterns. Their interpretations were questioned by H. Godwin and A. G. Tansley, who drew attention to the role of ecological variables (structure of plant communities and species physiology) and cultural parameters (wood selection) in determining species availability (Godwin and Tansley 1941). They also stressed the potential effects of differential wood combustion on taxon representation. Thus, the debate was launched for the first time, which continues to a certain degree to the present-day, concerning the appropriateness of archaeological wood charcoals for reconstructing prehistoric vegetation. That such early developments should take place in Britain is not surprising given the long-standing tradition of prehistoric and ancient wood studies on the British Isles, from the 17th century onwards, dealing mainly with the remains of waterlogged artefacts and woodworking (1,2) (for an overview of the early literature see Coles et al. 1978). These were matched later on by extensive and detailed studies on wood anatomy, initially addressed to botanists, foresters and timber experts but later proven invaluable to archaeobotanists interested in wood charcoal identification, such as ‘The Anatomy of The Dicotelydons’ by C. R. Metcalfe and L. Chalk (1950) and F. W. Jane’s ‘The Structure of Wood’ (1956).
Comparable events followed shortly afterwards in France, stimulated by a stronger interest of botanists and wood anatomists on archaeological charred wood macro-remains and their palaeoecological interpretation. Momot (1955) explicitly used wood charcoal macro-remains derived from late Palaeolithic hearth structures as a guide to reconstructing past climate patterns. In his treatise on the methodology of charcoal analysis, the French wood anatomist M. Couvert stressed the uniqueness of charcoal data in supplementing a picture of past vegetation essentially synchronous to prehistoric settlement, a quality not shared by pollen analytical investigations that usually offer a much more arbitrary sketch of woodland composition (Couvert 1968). His studies of charcoal specimens from the cave sites of Khanguet Si Mohamed Tahar and Tamar Hat in Algeria provided the first “hard” evidence for the existence of non-analogue vegetation types in this region during prehistoric times, which were interpreted as indicating different climate regimes in the past (Couvert 1969a, 1969b). Following a slightly different approach, in 1976 he published the results of his analysis of wood charcoals retrieved from the sixth millennium site of Relilaï in Algeria (Couvert 1976). In this paper, he attempted to reconstruct the spatial distribution of past vegetation based on modern rainfall values from wooded areas and topographic relief. His stated purpose was to reconstruct vegetation catchments, measure the distances people had to walk in order to collect wood and thus reconstitute their paths of movement.
A qualitative approach to vegetation reconstruction was proposed by another French botanist, S. Santa, in his synthesis of charcoal data from North Africa (Santa 1961). Based on the axiom that “the same floristic stock will generate identical vegetation groups” (i.e. if vegetation communities are defined as essentially a group of species, then the same range of species will give rise to identical floristic associations, now or in the past), he used qualitative data (namely lists of taxa compared to their modern distributions in the area of study) in order to reconstruct past vegetation formations . He was the first to introduce the concepts of the “probability” of preservation and the “possibility” of taxon recovery from the charcoal macro-remains. His answer to this problem was to exclude from his vegetation surveys species that were least likely to be collected by prehistoric groups (e.g. those that have poor heat value) or those which, due to their natural characteristics (e.g. small-sized woods), did not have a high chance of preservation in the archaeological record (Santa 1961: 56). The remaining taxa were then classified into different vegetation types according to their ecological status in modern day formations (as pioneer, dominant, climax or secondary species). These vegetation formations served as a comparative basis for the reconstruction of past vegetation.
After the Second World War, the widespread adoption of radiocarbon dating signalled a new focus on charred plant remains, particularly charcoal. However, the limitations of the existing laboratory techniques hampered exploiting the full potential of wood charcoals. The preparation of charcoal for microscopic identification involved the impregnation of charred specimens with paraffin or polyester, in order to stabilise individual fragments, and then with a synthetic resin so as to obtain small, transparent blocks enclosing each specimen. These were then sectioned with the aid of a microtome in the three anatomical planes (transverse, radial and tangential). The upper surface of the resulting pieces was subsequently abraded in order to produce thin sections that could be examined under a transmitted light microscope (for detailed description of the procedures followed see Momot 1955, Couvert 1968, Santa and Vernet 1968). Predictably, this extremely time-consuming method of laboratory preparation resulted in few and in some cases even problematic identifications, due to the distortion of anatomical characters. It also severely compromised the suitability of charcoal specimens for radiocarbon dating, due to the contamination caused by their chemical treatment.
At the end of the 1960s, the adoption of reflected light microscopy by charcoal analysts was bound to revolutionise the state of affairs within the discipline (Western 1969, 1971, Leney and Casteel 1975). In contrast to the impregnation methods, charcoal specimens are fractured either by hand or by using a razor blade in the three anatomical planes and examined directly under the microscope. Simplifying preparation techniques and microscopy procedures meant that it was now possible to identify a high number of specimens in a relatively short time. Therefore, it became realistic to undertake systematic studies of large wood charcoal assemblages, which could furthermore produce statistically meaningful results. These advances in laboratory procedures were in line with the widespread implementation in the field of various water flotation techniques (see also Pearsall 2000: 14-27), which enhanced dramatically the recovery and retrieval of charred plant macro-remains.
At the same time, the first major syntheses and systematic studies were produced in the Western Mediterranean, particularly in France, under the influence of Jean-Louis Vernet who was the founder of a strong research tradition centred on the University of Montpellier. During the 1980s and the 1990s, another generation of researchers laid the foundations for the systematic application of charcoal analysis on archaeological sites, with a renewed emphasis on appropriate sampling strategies and the need for charcoal analysts to have an active role in excavating and sampling archaeological sites. Further, new avenues were explored for the interpretation of charcoal data in relation to wood combustion experiments, ethnographic research and wood anatomical studies. Parallel to these developments was the expansion of the methodology in other Mediterranean countries as well, such as Portugal, Spain and Italy, in the rest of Europe, in Africa, the Near East, North and South America, etc. (e.g., Miller 1985, Smart and Hoffman 1988, Badal Garcia 1992, Neumann 1992, Willcox 1992, Chabal et al. 1999).
Badal-Garcia, E. (1992) L' anthracologie préhistorique: à propos de certains problèmes méthodologiques. Bulletin de la Société Botanique de France 139: 167-189.
Chabal, L., L. Fabre, J.-F. Terral, and I. Théry-Parisot (1999) “L' anthracologie,” in La botanique. Edited by C. Bourquin-Mignot, J.-E. Brochier, L. Chabal, et al., pp. 43-104. Paris: Errance.
Coles, J. M., S. V. E. Heal, and B. J. Orme (1978) The use and character of wood in prehistoric Britain and Ireland. Proceedings of the Prehistoric Society 44: 1-45.
Couvert, M. (1968) Étude des charbons préhistoriques. Méthodes de préparation et d' identification. Libyca 16: 249-256.
Couvert, M. (1969a) Étude de quelques charbons préhistoriques de la grotte Capelleti. Libyca 17: 213-218.
Couvert, M. (1969b) Identification de charbons provenant du gigement de Tamar Hat. Libyca 17: 49-52.
Couvert, M. (1976) Traduction des éléments de la flore préhistorique en facteurs climatiques. Libyca 24: 9-20.
Jane, F. W. 1956. The structure of wood. London: A. & C. Black.
Leney, L., and R. W. Casteel (1975) Simplified procedure for examining charcoal specimens for identification. Journal of Archaeological Science 2: 153-159.
Metcalfe, C. R., and L. Chalk (1950) Anatomy of the dicotelydons (2 vols.) Oxford: Clarendon Press.
Miller, N. F. (1985) Palaeoethnobotanical evidence for deforestation in ancient Iran: a case study of urban Malyan. Journal of Ethnobiology 5: 1-19.
Momot, J. (1955) Méthode pour l' étude de charbons de bois. Bulletin de la Société Préhistorique Française 52: 141-142.
Neumann, K. (1992) The contribution of anthracology to the study of the late Quaternary vegetation history of the Mediterranean region and Africa. Bulletin de la Société Botanique de France 139: 421-440.
Pearsall, D. M. (2000) Palaeoethnobotany: a handbook of procedures. 2nd edition. London: Academic Press.
Salisbury, K. J., and F. W. Jane (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.
Santa, S. (1961) Essai de reconstitution de paysages végétaux Quaternaires d'Afrique de Nord. Libyca 6-7: 37-77.
Santa, S., and J. L. Vernet (1968) Une technique de préparation des charbons de bois préhistoriques en vue de leur étude anatomique. Application. Naturalia Monspeliensia 19: 171-177.
Smart, T. L., and E. S. Hoffman (1988) “Environmental interpretation of archaeological charcoal,” in Current palaeoethnobotany. Edited by C. A. Hastorf and V. S. Popper, pp. 165-205. Chicago & London: University of Chicago Press.
Western, C. A. (1969) An attempt at the ecological interpretation of charcoals with special reference to material from Jericho. B.Sc. Dissertation, University of Oxford.
Western, C. A. (1971) The ecological interpretation of ancient charcoals from Jericho. Levant 3: 31-40.
Willcox, G. (1992) Bilan des données anthracologiques du Proche-Orient. Bulletin de la Société Botanique de France 139: 539-55.
® Eleni Asouti, 2006
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