Flax use, weeds and manuring in Viking Age Åland: archaeobotanical and stable isotope analysis

Vegetation History and Archaeobotany https://doi.org/10.1007/s00334-024-01029-0 ORIGINAL ARTICLE Flax use, weeds and manuring in Viking Age Åland: archaeobotanical and stable isotope analysis Santeri Vanhanen1 · Kristin Ilves2 Received: 29 January 2024 / Accepted: 28 August 2024 © The Author(s) 2025 Abstract Charred masses of nearly 100,000 Linum usitatissimum (flax) seeds were found in house remains from Tjudnäs on the Åland Islands, Finland, and radiocarbon dated to ad 880–1020. The flax seeds were large and discovered in lumps, which indicates that they had been pressed for their oil. The flax was accompanied by seeds of Cuscuta epilinum, Lolium remotum, Galium spurium and Camelina alyssum/sativa, which are specific weeds of flax fields that mimic it in the flax fields and during crop processing. Several of these species have now become extinct or rare after the introduction of more effective methods of weed control and less flax growing. This find demonstrates the antiquity of this obligate flax weed flora, which appears to have been introduced to Åland together with flax seeds intended for cultivation. Thousands of cereal grains discovered in Viking Age/early medieval (ad 750–1300) Kohagen show that a broad range of crops was grown, with high proportions of Triticum aestivum (naked wheat). Stable isotope analyses of carbon (δ13C) and nitrogen (δ15N) ratios were done on the flax from Tjudnäs and other crops from Kohagen, all from samples dated ad 880–1020. The analyses showed high values of δ15N, which can be explained by considerable soil enrichment with manure, possibly also with maritime resources such as seaweed and fish. The δ13C values varied between crops, with those for flax being lower than for cereals and Pisum sativum (peas), which could reflect different environmental conditions or differences in plant physiology. The factors affecting δ15N and δ13C in flax are, however, poorly understood due to the lack of experimental studies. Keywords Flax · Archaeobotany · Stable isotope analysis · Viking Age · Flax weeds · Manuring Introduction Lumps of charred Linum usitatissimum (flax) seeds with associated flax field weeds and thousands of charred cereal grains were found at the sites of Tjudnäs and Kohagen. Both sites are dated to around ad 1000 and are situated in the Åland Islands archipelago in the northern Baltic Sea, where the topography and suitability for growing crops have changed immensely over time due to isostatic land uplift (Fig. 1). The earliest growing of crops on the islands was Communicated by F. Bittmann. * Santeri Vanhanen 1 The Archaeologists, National Historical Museums, Odlarevägen 5, Lund 22660, Sweden 2 Department of Cultures, Faculty of Arts, University of Helsinki, Unioninkatu 38), P.O Box 59, Helsinki FI‑00014, Finland done by the maritime hunter-gatherers of the Pitted Ware Culture (Gropkeramisk kultur), ca. 3000 bc (Table 1), when the archipelago was formed of small islands and skerries (islets) (Vanhanen et al. 2019). During the Bronze Age, land areas grew gradually larger from the uplift and plant growing continued. Little is known about the farming of the Early Iron Age, but later on, during the Late Iron Age, an increase in population and farming activities is shown by the archaeological and pollen data (for example, Callmer 1994; Núñez 1995; Ilves 2018a; Alenius 2014; Larsson et al. 2023). For our period of study, the Late Iron Age (ad 550–1050), the area of the islands was 500–650 km2, which is only half of their current size (Núñez 1995). On the higher parts there are exposed areas of bare granite bedrock with settlements and graves. Fine sediments found lower down were suitable for growing crops. Cultivation of light soils, shown by the finds of ancient plough marks created with a simple ard (Núñez 1995), was complemented with slash-and-burn cultivation, as indicated in the pollen data (Alenius et al. 2024). Heavy clay soils appear to have been used as pastures or Vol.:(0123456789) Vegetation History and Archaeobotany Fig. 1  Left, location of the Åland Islands and the main islands; available land during the Late Iron Age shown in lighter grey; image from ESRI (Environmental Systems Research Institute). Lower left, map of Scandinavia with location of the sites. Right, location of the settlement sites of Tjudnäs and Kvarnbo Kohagen. Present-day arable Table 1  Archaeological periods and their dates for the Åland Islands Phase Neolithic Period/culture Kamkeramiska kulturen (Comb Ware) Gropkeramisk kultur (Pitted Ware) Pitted Ware/Corded Ware Kiukainen Ware Bronze Age Early Bronze Age Late Bronze Age Early Iron Age Pre-Roman Iron Age Roman Iron Age Migration Period Late Iron Age Merovingian Period Viking Age Medieval period Early Medieval Period Late Medieval Period Cal age 5500–3300 bc 3300−2800 bc 2800–2300 bc 2300–1500 bc 1500–1100 bc 1100–500 bc 500 bc–ad 1 ad 1–400 ad 400–550 ad 550–750 ad 750–1050 ad 1050–1300 ad 1300–1520 areas, which mainly consist of clay soils and tills shown in green. The shoreline shown here is roughly consistent with that of the end of the Late Iron Age, circa ad 1050. Map data from Maanmittauslaitos (The national land survey of Finland), maps drawn by Kristin Ilves meadows for making hay for fodder. The area of the lighter soils suitable for crops was, however, limited, and might not have been able to support a settlement only by farming (Jaatinen et al. 1989). This is reflected in archaeological findings indicating a mixed economy of animal husbandry, crop growing, fowling, fishing, hunting and trading (Storå et al. 2012; Ahola et al. 2014). According to earlier studies, Hordeum vulgare (barley) was the main crop, along with Avena (oats), Triticum aestivum (naked wheat), Secale cereale (rye), Cannabis sativa (hemp) and Linum usitatissimum (flax) (Núñez and Lempiäinen 1992; Andersson 2014, 2017; Lempiäinen-Avci 2021). Our finds from Tjudnäs and Kohagen add to this knowledge, showing the importance of naked wheat and flax at these sites. Flax was one of the earliest plants to be domesticated, in the Near East as one of the founder crops together with wheat and barley. Its journey northwards was prolonged and it occurred sporadically in northern continental Europe during the Neolithic and Early Bronze Age and became more Vegetation History and Archaeobotany common during the Late Bronze Age (Kirleis et al. 2012; Effenberger 2018). In Sweden and Åland the earliest flax is dated to the Late Bronze Age/Pre-Roman Iron Age transition, whereas in mainland Finland and Latvia the first finds are from the Roman Iron Age (Lempiäinen 2011; Viklund 2011; Karg 2012; Grikpėdis and Matuzeviciute 2020; Vanhanen 2020). Today, flax is mainly grown for the production of fibres and oil. Waterlogged flax stalks are interpreted as direct evidence of retting flax to produce fibres (Alsleben 1995; Viklund 2011), whereas masses of many charred seeds, such as the Tjudnäs find, are considered to indica (...truncated)