Durum wheat and barley yields in antiquity estimated from 13C discrimination of archaeological grains: a case study from the Western Mediterranean Basin

This study develops a novel approach by which to estimate cereal yields in ancient times based on the 13C discrimination (Δ) of ancient grains. First, a yield model based on Δ in grains from modern durum wheat (Triticum durum Desf.) and barley (Hordeum vulgare L.) crops was developed using a wide range of genotypes and Mediterranean environments. For both crops, a strong positive linear regression between yield on a logarithmic basis and the Δ of grains (r2 = 0.72, 506 d.f. for durum wheat and r2 = 0.50, 316 d.f. for barley) was observed; the slope of the relationship was significantly higher for durum wheat than for barley. Initial estimates of yield were subsequently corrected from bibliographical data to take into consideration the two major differences between ancient and modern crops unaccounted for by the Δ of ancient samples: atmospheric CO2 levels and the harvest index ratio. As a case study, this method was used to obtain estimates of ancient yields of durum wheat and barley in two areas of the Western Mediterranean Basin (NE and SE Iberian Peninsula) using Δ data of grain samples from a number of archaeological sites. These sites dated from the beginning of agriculture in these areas (Neolithic Age, ca 7500 years before present (BP)) to the Middle Ages (ca 800 years BP). Our results show the absence of a marked trend in the yields of both durum wheat and barley, which seem to have remained relatively high from the Neolithic to the Middle Ages. The average values for the whole period (mean ± SD) were 1.61 ± 0.49 and 1.08 ± 0.25 Mg ha–1 for durum wheat and barley, respectively in the NE Iberian Peninsula, and 1.18 ± 0.48 and 0.97 ± 0.30 Mg ha–1, respectively, in SE Iberian Peninsula. These yield estimates are within the range indicated by the limited data (mostly from contemporary written sources) available for the Mediterranean Basin, and suggest relatively good growing conditions throughout the period studied, particularly in the NE Iberian Peninsula.