RESEARCH PAPER Olive trees as bio-indicators of climate evolution in the Mediterranean Basin Marco Moriondo 1 , Giacomo Trombi 2 , Roberto Ferrise 2 , Giada Brandani 2 , Camilla Dibari 2 , Caspar M. Ammann 3 , Marta Mariotti Lippi 4 and Marco Bindi 2 * 1 Institute of Biometeorology, National Research Council of Italy, Via Caproni 8, 50145 Florence, Italy, 2 Department of Agri-food Production and Environmental Sciences, University of Florence, Piazzale delle Cascine 18, 50144, Florence, Italy, 3 Climate and Global Dynamics Division, National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80307-3000, USA, 4 Department of Evolutionary Biology, University of Florence, Via G. La Pira 4, 50121 Firenze, Italy ABSTRACT Aim This paper aims to project areas of olive cultivation into future scenarios. Accordingly, we first asked the question whether global circulation models (GCMs) are able to reproduce past climatic conditions and we used historical ranges of olive cultivation as a palaeoclimate proxy. Location The Mediterranean basin. Methods We used an ecological model, calibrated and validated for modern times, to test the reliability of a general circulation model (NCAR-CSM GCM) in reproducing past ranges of olive tree cultivation inferred from the literature, archaeo-botanical investigations and fossil pollen analyses. Results The re-constructions of olive growing areas, obtained for the Medieval Climate Anomaly (MCA, 1200-1300 AD) and the Little Ice Age (LIA, 1600-1700 AD) by coupling the outputs of NCAR-CSM to the ecological model, were in agreement to those observed. Simulations of olive growing areas for future time-windows showed that a northwards expansion of the species is expected to occur by 2100. Main conclusions These results demonstrate that the NCAR-CSM can provide an accurate reconstruction of past climate with results sensitive to climate forcing factors and thus, it is more likely to give reliable projections for the future. Addi- tionally, the warming and drying conditions expected in the coming decades may determine changes across the Mediterranean basin that is unprecedented. Keywords Ecological model, general circulation model, Little Ice Age, Medieval Climate Anomaly, Mediterranean, olive tree, Roman Climate Optimum. *Correspondence: Marco Bindi, Department of Plant, Soil and Environmental Science, University of Florence, Piazzale delle Cascine 18, 50144, Florence, Italy. E-mail: marco.bindi@unifi.it INTRODUCTION The strong relationships of olive-growing areas with Mediterra- nean climate, in addition to the absence of competitive interac- tions with other species and the role of human intervention in reducing the time lag between spatial changes in climate and crop distribution, allow for the consideration of cultivated areas of this species as a sensible indicator of temperature change for the entire Mediterranean Basin (Moriondo et al., 2008). Moreover, in the coming decades, the olive tree will face the greatest climatic change that has been recorded since its spread into the Mediterranean Basin, and as a result its cultivated area is expected to adapt to the predicted future climate. Aiming to project areas of olive tree cultivation into future climate conditions, we first used an ecological model, calibrated and validated for modern times, to test the accuracy of a general circulation model (NCAR-CSM GCM) in reproducing the past range of olive tree cultivation inferred from the literature, archaeo-botanical investigations and palaeo-palynological analyses. After passing this hindcast test, the ecological model was then applied to projecting what future olive cultivation extension might look like if exposed to a climate scenario (SRES A1b) simulated with the NCAR-CSM. MATERIAL AND METHODS Present and past areas of olive tree cultivation The current area of olive cultivation in the Mediterranean Basin was derived from land-cover maps and agricultural land-use statistics. For European countries, the Corine Land Cover 2000 Global Ecology and Biogeography, (Global Ecol. Biogeogr.) (2013) ••, ••–•• © 2013 John Wiley & Sons Ltd DOI: 10.1111/geb.12061 http://wileyonlinelibrary.com/journal/geb 1