If we could stand in the place our Mesolithic ancestors called home, what would we see around us? Researchers have developed a technique to determine whether the microhabitats surrounding archaeological sites were dense forests or more open grasslands by studying ancient hazelnut shells that have been preserved for thousands of years. This approach can reveal what local ecosystems looked like thousands of years ago and reveal the extent to which humans have impacted these natural environments over time.
Archaeologists study the carbon isotope values of hazelnuts in ancient sites to understand the characteristics of local woods.
Dr Amy Styring from the University of Oxford, lead author of the Frontiers in Environmental Archaeology paper, said: "By analyzing carbon in hazelnuts found in archaeological sites in southern Sweden, ranging from Mesolithic hunter-gatherer camps to one of the largest and richest Iron Age settlements in Northern Europe, we found that hazelnuts were harvested from an increasingly open environment."
For thousands of years, humans in Northern Europe have relied on the hazelnut tree as a source of material and food. Hazelnuts were a valuable resource for the people who collected hundreds of them at Mesolithic and Neolithic sites.
Dr. Karl Ljung, senior author of the article and from Lund University in Sweden, said: "Nuts are an excellent source of energy and protein that can be stored for long periods of time and eaten whole or ground. The shells can also be used as fuel."
Like all plants, hazel trees contain carbon, which exists in different forms, called isotopes. The ratio of different carbon isotopes changes depending on the ratio of carbon dioxide concentrations in the leaf cells and the surrounding environment. In plants such as hazel trees, this ratio is greatly affected by sunlight and water supply; in places where there is no shortage of water, such as Sweden, sunlight has an even greater impact on this ratio. In places where there are fewer other trees competing for sunlight and photosynthesis rates are higher, hazel trees will have higher carbon isotope values.
"This means that hazelnut shells found at archaeological sites can record the open environment at the time of collection. This in turn tells us more about the habitats in which people foraged for food at that time," explains Ljung.
Collect information
To test whether this effect was present in archaeological samples, the scientists collected hazelnuts from trees grown under different light levels at three locations in southern Sweden and analyzed changes in their carbon isotope values and how these values related to the light levels the trees were exposed to. They then studied the carbon isotope values of hazelnut shells also found in archaeological sites in southern Sweden. They selected shell fragments from four Mesolithic sites and 11 sites ranging from the Neolithic to the Iron Age, some of which were occupied in more than one period.
Using reference values and archaeological results, the archaeologists built a model that placed hazelnut samples into one of three categories: closed, open and semi-open. Because the carbon isotopes of an individual hazelnut will naturally differ slightly from those of other hazelnuts growing in similar environments, the scientists used multiple samples from each site and assessed the proportion of hazelnuts growing in closed or open environments.
Growth changes
Scientists have found that Mesolithic nuts were collected from more closed environments, while modern nuts were collected from more open environments. By the Iron Age, most of the people who collected hazelnut samples for this study were collecting nuts from open fields rather than woodlands, and their microhabitats had completely changed. This is consistent with the environmental reconstructions derived from pollen analysis, but where pollen records are sparse, isotope analysis can be used to visually describe the local environment.
"Our study opens up new possibilities for directly linking environmental changes to humans' foraging activities and reconstructing the microhabitats they exploited," said Styring. "We hope to directly radiocarbon date and carbon isotope measurements of hazelnut shells from more archaeological sites and environments. This will provide a more detailed understanding of past woodlands and landscapes, help archaeologists better understand human impacts on the environment, and perhaps help us think differently about the use and change of woodlands today."
Compiled source: ScitechDaily