Carlos Morla

Long-term persistence of Mediterranean pine forests in the Duero Basin (central Spain) during the Holocene: The case of Pinus pinaster Aiton

In the southern Duero Basin of central Spain, there are vast areas of aeolian sand sheets and dune fields. A comprehensive survey of the sand quarries in this area identified a number of palaeosols in sedimentary sequences. The identification and AMS radiocarbon dating of soil charcoal fragments collected in these palaeosols indicate the persistence of Pinus pinaster in this area throughout most of the Holocene. Although potential natural vegetation models have usually considered the Pinus pinaster forests in this inland area of artificial origin, soil charcoal analysis provides firm evidence of a natural origin. Our data fit perfectly with the pattern of Holocene vegetation development for inland areas of Iberia, which are characterised by stability of pine forests throughout the Holocene. Finally, the growing body of palaeobotanical evidence from Iberia (macrofossils and pollen) is contributing to improve our knowledge of P. pinaster ecology, showing that this species has been present in most Iberian regions during the Holocene, where it has inhabited areas characterised by a very diverse set of climatic and soil conditions.

Taxonomic composition of the Holocene forests of the northern coast of Spain, as determined from their macroremains

Eight sites distributed over a distance of some 400 km of the Cantabrian coast (northern Spain) provided 153 wood, 50 fruit and over 350 leaf remains belonging to the areas Holocene forests. The high taxonomic precision with which these macroremains were identified (in many cases at the species level), plus the accurate information available regarding the original growth locations of these plants, provide new geobotanical insights into the history of northern Spains Atlantic forests. Radiocarbon dating of the wood samples showed the collected material to have lived between 8550 and 800 cal. BP. Analysis of the macroremains showed the deciduous mixed forests of the Holocene to contain a majority of Quercus robur and Corylus avellana, accompanied by Acer pseudoplatanus, Ulmus minor, Castanea sp., and hygro-thermophilous taxa (Arbutus, Laurus and Vitis vinifera). The remains of hygrophilous communities, dominated by Salix atrocinerea, Alnus glutinosa and Fraxinus sp., show these to have expanded during the Holocene. The absence of conifer macroremains is interpreted as reflecting the disappearance of Würmian conifer populations at the beginning of the Holocene. The different taxa (eg, Ilex spp. and V. vinifera) that survived the last glaciation in the refugia offered by Spains northern coast persisted in the same areas during the Holocene. A leaf sample of Ulmus minor dating to 3950 ±120 cal. BP reveals for the first time the natural occurrence of this species on the northern coast of Spain.