Abstract The European high Alps are internationally renowned for their dairy produce, which are of huge cultural and economic significance to the region. Although the recent history of alpine dairying has been well studied, virtually nothing is known regarding the origins of this practice. This is due to poor preservation of high altitude archaeological sites and the ephemeral nature of transhumance economic practices. Archaeologists have suggested that stone structures that appear around 3,000 years ago are associated with more intense seasonal occupation of the high Alps and perhaps the establishment of new economic strategies. Here, we report on organic residue analysis of small fragments of pottery sherds that are occasionally preserved both at these sites and earlier prehistoric rock-shelters. Based mainly on isotopic criteria, dairy lipids could only be identified on ceramics from the stone structures, which date to the Iron Age (ca. 3,000–2,500 BP), providing the earliest evidence of this practice in the high Alps. Dairy production in such a marginal environment implies a high degree of risk even by today’s standards. We postulate that this practice was driven by population increase and climate deterioration that put pressure on lowland agropastoral systems and the establishment of more extensive trade networks, leading to greater demand for highly nutritious and transportable dairy products.

Citation: Carrer F, Colonese AC, Lucquin A, Petersen Guedes E, Thompson A, Walsh K, et al. (2016) Chemical Analysis of Pottery Demonstrates Prehistoric Origin for High-Altitude Alpine Dairying. PLoS ONE 11(4): e0151442. https://doi.org/10.1371/journal.pone.0151442 Editor: John P. Hart, New York State Museum, UNITED STATES Received: January 8, 2016; Accepted: February 29, 2016; Published: April 21, 2016 Copyright: © 2016 Carrer et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by The Archaeological Service of the Canton of Grisons, 7th EU framework Marie Curie Intra-European Fellowship (FP7-PEOPLE-2012-IEF), and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) of Brazil. Competing interests: The authors have declared that no competing interests exist.

Introduction Today, alpine dairying is both a multi-million euro industry and an important cultural tradition [1]. The production of dairy foods in the high Alps (>1,800 m) is inherently risky. It requires a close understanding of the mountain environment [2,3], careful management of livestock and a massive input of labour with the reward of nutritious, storable produce from seasonal pasture that would otherwise be unused. The recent history of alpine dairying is well documented [4] but due to the ephemeral nature of transhumance there is frustratingly little archaeological evidence, a problem exacerbated by the high mountain acidic geologies that lead to deterioration of any faunal remains. Consequently the origins of alpine dairying are still widely debated [5,6] and very little is known regarding the cultural, economic or environmental context that lead to its establishment. In Europe, we know from archaeological faunal assemblages and chemical evidence of dairy fats associated with pottery that milk production in lowland settings dates back to the Early Neolithic period when domesticated cattle and sheep were first introduced [7–9]. From this evidence, it has been much harder to establish the intensity or nature of dairying and its subsequent development. Early Neolithic ceramic sieves for separating curds and whey provide the strongest evidence for cheese production [10] and widespread reliance on fermented milk products is likely given that the ability to digest the sugars (lactose) in raw milk was an adaptation that probably only appeared in Europe during the Bronze Age [11]. In the circum-alpine lowlands, the earliest direct evidence of dairying comes from organic residues on pottery vessels dating to the late Neolithic of this region, ca. 6,000 BP [12,13]. Here, dairying was initially part of mixed economy that also included meat production with little evidence for specialization. From the start of the 3rd millennium BC, it has been hypothesised that dairying intensified with a range of interlinked innovations, that included greater reliance on ‘ante-mortem’ animal products such as wool and milk and the colonisation of poorer and less accessible land [14,15]. The little archaeological evidence for exploitation of high alpine environments that exists does not contradict this hypothesis. Seasonal occupation of high-altitudes intensified from the mid-3rd millennium BC to the 1st millennium BC (Bronze Age and Iron Age) and large dry stone structures begin to appear at this time [16–22]. These enclosures have been tentatively identified as animal corrals [16,23], but the near absence of any artefacts or animal bones means that their function is far from clear with no evidence to link these prehistoric sites to dairying. Indeed, prehistoric exploitation of such high altitude environments for dairying would seem to be remarkable given the high risk and sophisticated husbandry practices that are required, even by today’s standards. To explore further, we provide here the first chemical evidence for the use of prehistoric pottery in this extreme environmental setting. Molecular and stable isotope analysis of lipids extracted from pottery vessels are well established techniques for discriminating dairy fats in the archaeological record [7,10,24]. Unfortunately, ceramic vessels, that have been fundamental for establishing prehistoric dairying practices elsewhere in Europe, are not routinely recovered from high altitude sites and the few potsherds that have been found are small and highly fragmented (S2 Fig), partly due to the poor preservation of these sites. Nevertheless, thirty fragments from six highland archaeological sites (Table 1) of the Engadin region of southern Switzerland (Fig 1B) were obtained from securely 14C dated contexts from the 5th millennium BC (Neolithic) to the 1st millennium BC (S1 Text). This region is typical of the central-alpine environment, with valley bottoms above 1,000 m asl and high seasonal pastures ranging from around 2,000 m to 2,800 m asl (S1 Text). Five of the sites chosen are above 2,000 m asl and include early Neolithic and Bronze Age rock-shelters and the later Iron Age stone enclosure and hut (Table 1). PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 1. Location and chronology of the sites investigated in this study. Inset (A) location and chronology of the earliest upland dry-stone structures in the Alps with secure dates; the Iron Age Hut of Val Fenga during excavation (C). https://doi.org/10.1371/journal.pone.0151442.g001 PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Table 1. Main characteristics of the investigated sites and summary results of the analysis. https://doi.org/10.1371/journal.pone.0151442.t001

Materials and Methods The Archaeological Service of the Canton of Grisons (Switzerland) provided permits for the archaeological investigation of the sites considered in this study (2007–2014), as well as for the analysis of 30 archaeological potsherds collected at these sites. All the samples are still available for the replication of this study. Further information on the sites and ceramic sherds is available in Supporting Information (S1 Text, S1 and S2 Tables). Lipids were extracted and methylated in one-step with acidified methanol [25,26] in order to maximise recovery from the small samples available. Briefly, methanol (4 ml) was added to homogenized ceramic powder (1 g) drilled from the sherd surface and the mixture was sonicated for 15 min and then acidified with concentrated sulphuric acid (200 μl). The acidified suspension was heated in sealed tubes for 4 h at 70°C and then cooled, and lipids were extracted with n-hexane (3 × 2 ml) and directly analysed by GC-MS and GC-C-IRMS. GC-MS was carried out on all samples using a 7890A Series chromatograph attached to a 5975C Inert XL mass-selective detector with a quadrupole mass analyser (Agilent Technologies, Cheadle, UK). The carrier gas used was helium, and the inlet/column head-pressure was constant. A splitless injector was used and maintained at 300°C. The GC column was inserted directly into the ion source of the mass spectrometer. The ionisation energy of the mass spectrometer was 70 eV and spectra were obtained by scanning between m/z 50 and 800. Aliquots of these extracts were initially analysed using a DB-5ms (5%-phenyl)-methylpolysiloxane column (30 m × 0.250 mm × 0.25 μm; J&W Scientific, Folsom, CA, USA). The temperature for this column was set at 50°C for 2 min, then raised by 10°C min-1 to 325°C, where it was held for 15 min. For GC-C-IRMS we use the instrumentation, conditions and protocols previously described in Craig et al. [24]. Instrument precision on repeated measurements was ±0.3‰ (s.e.m.) and the accuracy determined from FAME and n-alkane isotope standards was ±0.5‰ (s.e.m.). Modern reference samples were further corrected for the burning of fossil fuels to allow comparison with archaeological data. All δ13C values are relative to Vienna PeeDee Belemnite (VPDB) international standard. Correlations between the frequency and abundance of saturated and unsaturated FAMES were explored using PCA (variance-covariance test) in PAST 3.x [27]. Solvent extraction was undertaken where sufficient sample remained. Homogenized ceramic powders (1 g) were sonicated three times with DCM:MeOH (2:1, v/v). These total lipid extracts were combined, and evaporated to dryness under a stream of N2 and silylated with excess BSTFA + 1% TMCS at 70°C for 1 h, and then evaporated to dryness. The silylated solvent extracts were analysed by high temperature GC-MS using a DB1-HT (15 m x 0.32 mm, 0.1 mm film thickness; Agilent, UK). The temperature program was a 50°C isothermal hold followed by an increase to 350°C at 10°C min-1, followed by a 10 min isothermal hold.

Conclusions The development of high altitude dairying represents a new form of niche construction: the manipulation of part of a landscape for specific economic activities [51], i.e. the production of highly nutritious resource that can be easily transported and exchanged. This strategy has contributed to managing and preserving the upland environments over time, and is currently contributing to promoting cultural and gastronomic tourism. Remarkably, these high altitude environments have sustained dairy based pastoralism for over 3,000 years. Alpine cheese is renowned to have a long and complex history, that made it an essential feature of alpine cultural heritage [1]. This study showed that its origin can be traced back to prehistory, and that it is deeply related to the socio-economic development of alpine communities and to the transformation of upland landscapes. This research demonstrates the long-term resilience and persistence of the landscape management strategies associated with dairying activity, a form of anthropic landscape which has stood the test of time. Nowadays it is threatened by climate change and new supranational economic food production strategies that ignore, or are unaware of the complex, successful forms of local environmental knowledge and associated food production practices [52]. Therefore, the promotion of protection policies for traditional alpine cheeses and upland landscapes has to consider their long-term mutual correlation, which this study has dated back to the prehistoric period.

Acknowledgments We thank Christoph Walser for providing the map of the study area. All necessary permits were obtained for the described study, which complied with all relevant regulations. The authors want to thank the editor, Dr. Nora Reber and one anonymous reviewer for their constructive comments, which improved the quality of the manuscript.

Author Contributions Conceived and designed the experiments: TR OEC. Performed the experiments: FC ACC AT AL. Analyzed the data: OEC KW EPG AL ACC FC. Wrote the paper: FC OEC ACC AL KW. Commented on the final manuscript: EPG AT TR.