We present a novel approach to study the sustainability of ancient Mediterranean agriculture that combines the measurement of carbon isotope discrimination (D 13 C) and nitrogen isotope composition (d 15 N) along with the assessment of quality traits in fossil cereal grains. Charred grains of naked wheat and barley were recovered in Los Castillejos, an archaeological site in SE Spain, with a continuous occupation of ca. 1500 years starting soon after the origin of agriculture (ca. 4000 BCE) in the region. Crop water status and yield were estimated from D 13 C and soil fertility and management practices were assessed from the d 15 N and N content of grains. The original grain weight was inferred from grain dimensions and grain N content was assessed after correcting N concentration for the effect of carbonisation. Estimated water conditions (i.e. rainfall) during crop growth remained constant for the entire period. However, the grain size and grain yield decreased progressively during the first millennium after the onset of agriculture, regardless of the species, with only a slight recovery afterwards. Minimum d 15 N values and grain N content were also recorded in the later periods of site occupation. Our results indicate a progressive loss of soil fertility, even when the amount of precipitation remained steady, thereby indicating the unsustainable nature of early agriculture at this site in the Western Mediterranean Basin. In addition, several findings suggest that barley and wheat were cultivated separately, the former being restricted to marginal areas, coinciding with an increased focus on wheat cultivation.

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Carbon isotope discrimination (∆) was determined for kernels of six-row barley and durum wheat cultivated in the western Mediterranean basin during the last seven millennia. Samples came from different archaeological sites in Catalonia (north-east Spain) and in the south-east of Spain (mainly eastern Andalusia). Samples from the present were also analysed. Mean values of ∆ for barley and durum wheat grains decreased slightly from Neolithic (7000-5000 BP) to Chalcolithic-Bronze (5000-3000 BP) and Iron ages (3000-2200 BP) both in Catalonia and in south-east (SE) Spain. Values were consistently lower in SE Spain than in Catalonia throughout these five millennia, which suggests that Catalonia was less arid than SE Spain in this period. Within a given region, current discrimination values for kernels of the same cereal species cultivated under rainfed conditions were lower than those of archaeological grains, which implies more arid conditions at present. Furthermore, an empirical relationship between ∆ of mature kernels and total precipitation (plus irrigation where applicable) during grain filling (r 2 ϭ 0.73, N ϭ 25) was established for barley, currently cultivated at different locations in the western Mediterranean basin in Spain. The resulting relationship was applied to the ∆ data for barley kernels from 10 archaeological sites in Catalonia and 10 sites in SE Spain, to estimate the precipitation during grain filling at the time the kernels were produced. For both regions, current climatic conditions are consistently more arid than those inferred for the Neolithic, Bronze and Iron ages. In addition, although Catalonia was estimated to have had consistently wetter conditions (about 20% more precipitation) than SE Spain throughout these millennia, differences in precipitation between these two regions have recently increased, with 79% more precipitation in Catalonia. Results indicate a more rapid increase in aridity in SE Spain than in Catalonia, probably produced during the last few centuries, and due to anthropogenic causes.Abbreviations ∆, stable carbon isotope discrimination; δ 13 C, ratio of CO 2 ; WUE, water-use efficiency; BP, before present; NE Spain, north-east of Spain; SE Spain, south-east of Spain; 13 C/ 12 C relative to PeeDee belemnite standard; p i /p a, ratio of intercellular to atmospheric partial pressure of VPD, vapour pressure deficit.

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Recibido el 15 de marzo de 2013. Aceptado el 12 de septiembre de 2013 INTRODUCCIÓNEl Último Máximo Glacial (UMG o LGM) supone uno de los periodos con clima más frío del Planeta. No obstante, en las condiciones climáticas y, en especial, en la distribución de la temperatura, influye de manera notoria la latitud y la altitud, creando los grandes cinturones climáticos de la Tierra. Las latitudes altas concentraron los grandes casquetes glaciares lo que precipitó el descenso latitudinal y altitudinal de los climas fríos y templados (Frenzel et al. 1992; Lowe y Walker 1997) y con ellos las faunas y floras frías se expandieron hacia el sur. Las tres penínsulas mediterráneas (Ibé-rica, Itálica, Balcanes) se han postulado como zonas refugio de las especies templadas y cálidas a partir de datos políni-cos y faunísticos (Willis y van Andel 2004). Recientemente, los análisis antracológicos se han unido a esta problemática (Badal et al. 2012;Carrión et al. 2010; González et al. 2010; Ntinou 2002) corroborando estos resultados. Resumen. Se presentan estudios antracológicos de yacimientos de la península Ibérica con el objetivo de conocer la flora durante el Solutrense y, a partir de ella, las condiciones termoclimáticas y ombroclimáticas. Con los datos publicados e inéditos se demuestra que los refugios de las especies más cálidas están al sur del paralelo 40º N. La flora identificada en los carbones se puede agrupar en cuatro categorías: criófilas, termófilas, matorral y ribera. Se observa un gradiente latitudinal de la distribución de los marcadores más térmicos como Pinus pinea, Rosmarinus officinalis, mientras que los pinos criófilos están distribuido por todas las regiones. Se propone la identificación botánica de los carbones antes de hacer una datación radiométrica sobre ellos y publicar dicha identificación junto a la fecha radiocarbono para conocer la historia de las plantas y su distribución peninsular.