THE HISTORY OF THE HOLOCENE VEGETATION IN NORTHERN SPAIN FROM POLLEN ANALYSIS

1 Pollen diagrams from four peatbogs and a marshland located in the Atlantic and Mediterranean zones of north-central Spain are described, and their correlation is used to define a Holocene pollen reference sequence for the region. 2 Two main variants may be defined for the reference sequence: a northern variant, characterized by the predominance of deciduous trees, corresponds to sites under Atlantic temperate and moist climatic influence and a southern variant, with lower deciduous tree diversity, corresponds to sites under Mediterranean and continental climatic conditions. A vegetation gradient from the Atlantic to the Mediterranean side may be inferred from the pollen analysis. 3 A compilation of C-14 dated pollen diagrams from the northern Iberian Peninsula is used to plot maps for the Holocene spread of the principal tree genera. 4 Quercus, Corylus, Alnus, Taxus and Pinus had a wide distribution in the northern Iberian Peninsula during pre-Holocene times, as patchy refugia situated at medium elevations. They spread from these refugia at different times depending on climatic, geomorphological and successional conditions. Fagus, Abies and Carpinus could have spread through the Pyrenees. 5 Anthropogenic disturbance at the range limit of Fagus, Abies and Carpinus is probably responsible for their present geographical distribution. 6 The present-day Finns silvestris forests growing in the Iberian Cordillera, southern Pyrenees and Cantabrian Cordillera have a local origin and may constitute the Mediterranean mountain pine forest altitudinal zone, not previously described for the Iberian Peninsula.