Stable isotope data from archaeological hazelnut shells in Early–Mid-Holocene southern Scandinavia

This dataset contains the stable isotope data used in the study Hazelnut shell isotope values support vegetation openness in Mid-Holocene southern Scandinavia. It includes archaeological hazelnut shells from six Mesolithic sites in Denmark. The dataset contains original laboratory δ¹³C and δ¹⁵N measurements, sample information, and processed Δ¹³C values used to investigate local vegetation structure and canopy openness. Raw δ¹³C values were corrected for changes in atmospheric CO₂ and, for charred samples, for the effect of charring. The resulting Δ¹³C values were compared with modern hazelnut reference data and classified as representing open, semi-open, or closed-canopy growing conditions. The Excel workbook includes a README, site coordinates, raw isotope measurements, and converted Δ¹³C data. The dataset supports transparency and reproducibility of the associated study and can be reused in research on Holocene vegetation, woodland structure, palaeoecology, and human–environment interactions.