The spread of deciduous Quercus throughout Europe since the last glacial period

For most of the last glacial period, which ended about 10 ka BP2, the temperate forest species were restricted to small areas (termed refugia) with a milder climate, situated mostly along the Mediterranean borderlands and around the Black Sea. Species only started to expand from these glacial period refugia with the large-scale shifts in the global climate in the late-glacial (15-10 ka BP) and the beginning of the Holocene period (10 ka BP to present). Fossil pollen data from sites across Europe have been used to reconstruct the location of refugia of the deciduous oak species, and the spread from these refugia into their current ranges. Three areas of southern Europe have been identified as refugia for deciduous Quercus: southern Iberian peninsula, southern Italian peninsula and the southern Balkan peninsula. The spread of Quercus took place in two steps. First, in the late-glacial interstadial (13-11 ka BP) Quercus spread to the central European mountains from these refugia. Second, with the stabilisation of a climate favourable to deciduous trees species in the Holocene, oak spread into northern Europe, rapidly into the north-west, and more slowly into the centre and east, due to physical barriers. The earlier distribution changes are strongly correlated with the shifts in climate, whereas the later changes are most strongly controlled by competition between species, landscape topography and other edaphic factors. By approximately 6 ka BR the deciduous oak had reached its maximum extension in Europe. Two types of refugia have been identified from the observed range expansion: primary, full glacial refugia; and secondary, temporary refugia, which supported populations of the oak during the short, climatically unfavourable late-glacial stadial. (C) 2002 Elsevier Science B.V. All rights reserved.