Charcoal analysis from Iron age sites: a multi-scalar approach combining taxonomic identification, dendrology and taphonomy

Vegetation History and Archaeobotany https://doi.org/10.1007/s00334-025-01047-6 ORIGINAL ARTICLE Charcoal analysis from Iron age sites: a multi-scalar approach combining taxonomic identification, dendrology and taphonomy María Martín-Seijo1 · Miguel Ángel Vidal Lojo2 · Xosé Ignacio Vilaseco Vázquez3 Received: 6 August 2024 / Accepted: 20 December 2024 © The Author(s) 2025 Abstract Charcoal is the most common archaeobotanical remain recovered from the Iron Age archaeological contexts in the northwest of the Iberian Peninsula. This paper proposes a methodology that combines taxonomic identification together with the recording of dendrological and taphonomic attributes. The results obtained from six case studies– including on-site and off-site samples– dating between the 10th century bce and the 2nd century ce have provided multi-scalar information that can be analysed at the macro-scale (site), semi-micro scale (stage of site life-cycle), and micro-scale (functional context). This comprehensive methodology has extended the type and quality of archaeobotanical data provided by charcoal analysis, obtaining information not only about the management of woody resources, but also about aspects related to depositional and post-depositional alterations, combustion processes, plant growth conditions, and the presence of decayed wood in archaeological contexts. Our results show that samples collected from primary and secondary/tertiary contexts in Iron Age sites gave similar and complementary results. Data obtained from fire events showed percentages of charcoal vitrification and higher percentages of decayed wood. This study shows the importance of understanding the formation process of each individual context or even stratigraphic unit in order to adequately interpret the archaeobotanical data from it. Analysing anthracological data only at the site level is not informative enough to understand how wood resources were managed during their entire life-cycle, from the gathering of firewood or timber to its final disposal as debris. Keywords Charcoal analysis · Vitrification · Decayed wood · Functional contexts · Taphonomy · Iron age Introduction Charcoal is the most common type of archaeobotanical remains recovered from archaeological contexts in southern Europe. In this geographical area, the majority of Iron Age palaeoecological and palaeoethnobotanical data have been Communicated by C. Lancelotti. María Martín-Seijo 1 Instituto de Ciencias del Patrimonio (INCIPIT), Consejo Superior de Investigaciones Científicas (CSIC), Edificio Fontán, Bloque 4 Monte Gaiás, s/n, Santiago de Compostela 15707, Spain 2 Independent Archaeologist, Lugar Cabío 24, A Pobra do Caramiñal 15940, Spain 3 Servizo de Arqueoloxía, Complexo administrativo de San Caetano, Edificio 3, Andar 2, Xunta de Galicia, Santiago de Compostela 15781, Spain provided by this archaeobotanical evidence (for example, Figueiral 1995, 1996; Carrión Marco 2005; Martín-Seijo 2013; Vaz et al. 2017). Wood charcoal analysis provides data to reconstruct past woodland vegetation dynamics and human impacts on the landscape (Kabukcu 2018), although it is often underestimated as a tool in archaeological studies (Barnett 2020), due to the complexity of interpreting anthracological results. Charcoal assemblages recovered from archaeological contexts are the result of the convergence of various natural and anthropic processes, and require a careful interpretation, as they do not provide direct information about past vegetation, nor about firewood or wood selection by past communities (Théry-Parisot et al. 2010). Their complexity becomes apparent when comprehensive studies of samples move down from the macro-scale level (site) to the micro-scale level (functional context, stratigraphic unit or even sample) (Martín-Seijo et al. 2020). Understanding taphonomic processes involved in the formation of charcoal assemblages is crucial for refining our palaeoecological and palaeoethnobotanical interpretations, 13 Vegetation History and Archaeobotany and even for selecting for comparison archaeological contexts with similar ways of formation. This taphonomic approach is relevant not only for archaeobotanical research, but also for archaeology, as charcoal remains contain relevant information that may be recorded and integrated with other data provided by non-perishable archaeological evidence such as pottery and other finds (Martín-Seijo et al. 2017). Going beyond taxonomic identification is a methodological approach to better understand archaeological contexts, and consequently, to obtain more accurate data to understand past landscapes and to define past relationships between plants and people. The recording of dendrological attributes together with charcoal analysis was defined by Marguerie and Hunot (2007) in a methodological proposal that has been widely used in archaeobotanical research (for example, Heiss and Oeggl 2008; Euba et al. 2016; Wright 2018; VidalMatutano et al. 2020; Bleicher and Staub 2023). Recent research projects have led to methodological advances in the analysis of dendrological attributes to provide information about wood diameter estimation (Dufraisse et al. 2018, 2020), quantification of tyloses (Dufraisse et al. 2018), or woodland management practices (Girardclos et al. 2018; Dufraisse et al. 2022). Experimentation has been one of the main approaches used to understand the processes behind alterations of wood anatomy such as wood tissue vitrification (Vidal-Matutano et al. 2019; Courty et al. 2020) or radial cracks (Théry-Parisot and Henry 2012). Other aspects related to the taphonomy of wood before charring such as biodeterioration have also been approached by analysing archaeological evidence, both direct (Moskal-del Hoyo et al. 2010; Fohrer et al. 2017; Martín-Seijo 2024; Toriti et al. 2024) and indirect (Pastor Quiles et al. 2022). This article brings together data from six case studies from northwest Iberia, including on-site and off-site samples, to demonstrate the integration of archaeological and archaeobotanical information from charcoal assemblages recovered from sites with complex formation processes, such as those dated to the Iron Age. The selection of this geographical area and chrono-cultural framework is based on: (1) the diversity and complexity of archaeological features within Iron Age sites, which are associated with an increasing diversity of production and maintenance activities related to the use of pyrotechnology; (2) the existence of long-lasting occupations in the same place producing superimposed layers; (3) the recurrent identification of fire events at the sites and in their surroundings; (4) the introduction of technological innovations and new iron tools which had a profound impact on woodland management and woodworking techniques, and finally; (5) the increasing impact of human communities on their plant environment during the 1st millennium bce. The main aims of this pa (...truncated)