MEDITERRANEAN VEGETATION, LAKE LEVELS AND PALEOCLIMATE AT THE LAST GLACIAL MAXIMUM

International audienceTHE apparent conflict between pollen evidence for widespread Artemisia steppe1-6 (implying semi-arid conditions) and geomorphological evidence for high lake levels4,7-11 has produced controversy about the ice-age palaeoclimate of the Mediterranean region. Here we use a water-balance model12 (to predict catchment runoff ) and a biome model13 (to predict vegetation type) to reconstruct the palaeoenvironment around Lake Ioannina-a type locality for the northern Mediterranean region. We show that both sets of evidence are compatible with a summer-dry, winter-wet regime with seasonal temperature anomalies similar to those predicted by atmospheric model simulations of the Last Glacial Maximum14-18. The drying effect of the cold North Atlantic Ocean may have been counteracted in winter by increased storm frequency under a southward-shifted jet stream, as shown by several atmospheric models16-18

A new scenario for the Quaternary history of European beech populations: palaeobotanical evidence and genetic consequences

Here, palaeobotanical and genetic data for common beech (Fagus sylvatica) in Europe are used to evaluate the genetic consequences of long-term survival in refuge areas and postglacial spread. Four large datasets are presented, including over 400 fossil-pollen sites, 80 plant-macrofossil sites, and 450 and 600 modern beech populations for chloroplast and nuclear markers, respectively. The largely complementary palaeobotanical and genetic data indicate that: (i) beech survived the last glacial period in multiple refuge areas; (ii) the central European refugia were separated from the Mediterranean refugia; (iii) the Mediterranean refuges did not contribute to the colonization of central and northern Europe; (iv) some populations expanded considerably during the postglacial period, while others experienced only a limited expansion; (v) the mountain chains were not geographical barriers for beech but rather facilitated its diffusion; and (vi) the modern genetic diversity was shaped over multiple glacial-interglacial cycles. This scenario differs from many recent treatments of tree phylogeography in Europe that largely focus on the last ice age and the postglacial period to interpret genetic structure and argue that the southern peninsulas (Iberian, Italian and Balkan) were the main source areas for trees in central and northern Europ