Direct evidence for agricultural intensification during the first two millennia AD in northeast Burkina Faso

Archaeobotanical evidence from archaeological sites in northeast Burkina Faso dating to the first and second millennia AD has provided a useful insight into crop cultivation and the development of the West African savanna landscape. Nitrogen isotopic analysis of charred pearl millet grains from the same sites now provides the first opportunity to investigate how increased crop production and permanence of cultivated fields related to the intensity of household waste/manure application. Nitrogen isotope values of pearl millet grains increased during the first two millennia AD, indicating an intensification of manuring that would have enabled soil to stay fertile for longer, reducing the agricultural footprint of shifting cultivation. This may have been advantageous as population and settlement density increased, thereby increasing competition over land. The intensity of manure application in the second millennium AD at sites close to the Mare d'Oursi suggests that manure was likely sourced from outside the farming settlements, from livestock herded by nomadic pastoralists who would have been drawn to the mare for water. This is rare evidence for specialisation of sedentary farmers and pastoralists, demonstrating how the novel combination of fruit/seed, charcoal, faunal and isotopic evidence used in this study can enrich our knowledge of past lifeways in West Africa

Centralisation and long-term change in farming regimes: Comparing agricultural practices in Neolithic and Iron Age south-west Germany

This study uses two novel archaeobotanical techniques – crop carbon and nitrogen isotope analysis and functional weed ecology – to determine directly how the intensity of agricultural practice changed from the Neolithic to the early Iron Age in south-west Germany, with the emergence of fortified hilltop settlements (Fürstensitze or chiefly seats) regarded as the first urban centres in central Europe. The crop isotope and functional weed ecological evidence suggest that surplus cereal production in the early Iron Age was achieved through sustained use of manure combined with expansion in arable cultivation, both developments that are connected with more widespread use of animal traction. The increased scale of cultivation is broadly apparent across rural as well as fortified hilltop centres in the early Iron Age, and considerable variability in manuring intensity is consistent with agricultural decision-making at a local level rather than centralised control. Additionally, the more intensive manuring of hulled six-row barley, used in beer production, demonstrates that the political importance of drinking and feasting in early Iron Age society was reflected in crop husbandry practices. In terms of animal husbandry, faunal isotope data reveal a radical decrease in forest cover, potentially reflecting an expansion in the scale of herding accompanying that of arable cultivation. Site-specific patterning points to a range of herding strategies, from specialised herding of cattle at the Heuneburg to generalised patterns of livestock management at rural sites

Revisiting the potential of carbonized grain to preserve biogenic 87Sr/86Sr signatures within the burial environment

Strontium (Sr) isotope analysis of archaeological crops is a potential method of provenancing and identifying the movement of crops in the past, but there remains uncertainty about whether original 87Sr/86Sr values can be obtained from carbonized buried grains. We have determined that hydrochloric acid (HCl) leaching removes some, but not all, exogenous Sr from carbonized cereal grains buried in soil for up to one year. We conclude that while further work could refine the leaching method, Sr isotope analysis of archaeological cereal grains can distinguish crops sourced from outside a particular (e.g., local) area if it can be shown that leaching moves grain 87Sr/86Sr values significantly away from the expected Sr signature

Movement of agricultural products in the Scandinavian Iron Age during the first millennium AD: 87Sr/86Sr values of archaeological crops and animals in southern Sweden

In this paper, we examine the exchange of crops and livestock through the application of strontium (87Sr/86Sr) isotope analysis on cereal grains and faunal tooth enamel from the regional center of Uppåkra and three nearby settlements in Scania, southern Sweden, dating to the first millennium AD. Around a third of the fauna have non-local 87Sr/86Sr values, indicating the import of livestock from several different regions. After cleaning, almost all of the cereal grains have non-local 87Sr/86Sr values, which is surprising given the nearby abundance of fertile agricultural soils. We therefore suggest considering non-locally grown crops to be those whose 87Sr/86Sr values fall outside the normal distribution; if this approach is used, around 20% of the analyzed crop samples are interpreted as having grown non-locally. This study demonstrates the potential of combining strontium isotopic data of archaeobotanical and zooarchaeological material for gaining insights into the movement of agricultural products in prehistory

Carbon isotope values of hazelnut shells: a new proxy for canopy density

Hazel (Corylus avellana) has been abundant in the vegetation of northern and central Europe since the early Holocene and has provided food and materials for humans ever since. Here we use stable carbon isotope (δ13 14 C) values of hazelnut shells to infer woodland openness based on the premise of the “canopy effect”. It is well established that plants growing in dense, shaded forests have lower carbon isotope (δ13C) values than plants growing in open areas. By measuring δ13 C values in hazelnuts collected from trees growing in different levels of light intensity, we show that the canopy effect is preserved in hazelnuts and that their δ13 C values can be used to infer woodland openness in the past. We apply the method to hazelnuts recovered from sites dated to between the Mesolithic and Iron Age (c. 7000 BCE to 1000 CE) in southern Sweden. Our results show that the nuts dated to the Mesolithic were harvested from hazels growing in a range of closed to open settings while nuts from subsequent periods were harvested from progressively more open environments. Given the abundance of hazelnuts recovered from many archaeological contexts, this method has the potential to reconstruct the microhabitats exploited by humans in the past and explore the impact of humans on their environment

Nitrogen isotope values of Pennisetum glaucum (pearl millet) grains: towards a reconstruction of past cultivation conditions in the Sahel, West Africa

The nitrogen isotope compositions of charred wheat and barley grains reflect manuring intensity and have been used to reconstruct past manuring practices at archaeological sites across Europe and western Asia. To assess whether this analytical method can be applied to a staple crop in the West African Sahel, the nitrogen isotope values of Pennisetum glaucum grains in this region were determined and the effect of charring ascertained. Pennisetum glaucum ears were collected from fields in northeast Senegal, where the fertilisation histories of the plots (manure and/or household waste) were known. The nitrogen isotope values of these millet grains provide an insight into the values to expect for P. glaucum grains grown with low to moderate addition of manure/household waste in a semi-arid climate. Charring of P. glaucum grains by heating at 215–260 °C for 4–24 h increases their nitrogen isotope values by a maximum of 0.34‰. In light of these modern data, the nitrogen isotope values of millet grains recovered from the archaeological settlement mound of Tongo Maaré Diabal, Mali, can be interpreted as evidence for modest levels of manure/household waste input throughout the occupation of the site from cal AD 500–1150. This study demonstrates the potential for nitrogen isotope values of P. glaucum grains to shed light on past farming practices in West Africa

Combining functional weed ecology and crop stable isotope ratios to identify cultivation intensity: a comparison of cereal production regimes in Haute Provence, France and Asturias, Spain

This investigation combines two independent methods of identifying crop growing conditions and husbandry practices-functional weed ecology and crop stable carbon and nitrogen isotope analysis-in order to assess their potential for inferring the intensity of past cereal production systems using archaeobotanical assemblages. Present-day organic cereal farming in Haute Provence, France features crop varieties adapted to low-nutrient soils managed through crop rotation, with little to no manuring. Weed quadrat survey of 60 crop field transects in this region revealed that floristic variation primarily reflects geographical differences. Functional ecological weed data clearly distinguish the Provence fields from those surveyed in a previous study of intensively managed spelt wheat in Asturias, north-western Spain: as expected, weed ecological data reflect higher soil fertility and disturbance in Asturias. Similarly, crop stable nitrogen isotope values distinguish between intensive manuring in Asturias and long-term cultivation with minimal manuring in Haute Provence. The new model of cereal cultivation intensity based on weed ecology and crop isotope values in Haute Provence and Asturias was tested through application to two other present-day regimes, successfully identifying a high-intensity regime in the Sighisoara region, Romania, and low-intensity production in Kastamonu, Turkey. Application of this new model to Neolithic archaeobotanical assemblages in central Europe suggests that early farming tended to be intensive, and likely incorporated manuring, but also exhibited considerable variation, providing a finer grained understanding of cultivation intensity than previously available

Isotopic and microbotanical insights into Iron Age agricultural reliance in the Central African rainforest

The emergence of agriculture in Central Africa has previously been associated with the migration of Bantu-speaking populations during an anthropogenic or climate-driven ‘opening’ of the rainforest. However, such models are based on assumptions of environmental requirements of key crops (e.g. Pennisetum glaucum) and direct insights into human dietary reliance remain absent. Here, we utilise stable isotope analysis (δ13C, δ15N, δ18O) of human and animal remains and charred food remains, as well as plant microparticles from dental calculus, to assess the importance of incoming crops in the Congo Basin. Our data, spanning the early Iron Age to recent history, reveals variation in the adoption of cereals, with a persistent focus on forest and freshwater resources in some areas. These data provide new dietary evidence and document the longevity of mosaic subsistence strategies in the region