High-altitude vegetational pattern on the Iberian Mountain Chain (north-central Spain) during the Holocene

Pollen, plant macrofossil, charcoal, sedimentary analyses and magnetic susceptibility measurements have been carried out on a C-14 dated sediment sequence from Las Pardillas Lake (1850 m a.s.l., Iberian Mountain Chain). The interpretation of the pollen diagram has been assisted by the analysis of an altitudinal transect of moss-polsters collected in the same area. After 9310 BP, a Pinus-Betula-Quercus open woodland developed. Between c. 9000 BP and 7100 BP, the woodland became a mixed forest with Pinus sylvestris. The beginning of the continuous curve of Corylus c. 9000 BP dated the local population expansion of this tree and is 1000 yeats earlier than the age previously attributed to its expansion in north-central Spain. At c. 7400 BP a local fire is associated with a possible first establishment of Fagus in the area. From c. 7100 BP to c. 3700 BP, Taxus, Ilex and Hedera were present in the forest vegetation. During this interval, the pollen and sedimentological record indicated a stable period of rich, mixed Quercus forest. At the same time, the community of floating-leaved aquatics was replaced by submerged plants, suggesting that a rise in lake water level may have occurred between 7200 and 6400 BP. Fagus became continuously present in the Las Pardillas Lake area c. 3200 BP. As Fagus is fire-sensitive, the expansion and stand scale establishment may be linked to an increase in fire regime, a type of disturbance which has facilitated the spread of this taxon elsewhere in Europe. A significant forest reduction, involving all the trees, took place c. 1500 BP. Between 1000 and 400 BP, Pinus and Fagus re-expanded associated with the first clear evidence of agricultural activity. The well-represented mixed Quercus forest around Las Pardillas Lake, and the early development of Corylus compared to other Mediterranean zones, suggests that oceanic conditions prevailed on the northern slopes of these mountains in north-central Spain.