La historia holocena de los pinares montanos en la Cordillera Cantábrica

Abstract

There are very few mountains in Western Europe which do not have a well-developed tier of vegetation in which mountain conifers play the main role in natural forest vegetation. The Cantabrian Mountain range is one of those exceptions, which Willkomm and Lange hastened to highlight the 19th century, assuming the possible relict character of the few mountain pine groves then existing in the Cantabrian Mountains. The palaeobotanic sites of the Late-Glacial and early Holocene with macroremains of mountain pines in the mountain range are very numerous: the Pinus genus is the main player in forest recovery during this period in most of the north of the Peninsula, forming woods both in the mountains and in wide zones of the Douro river basin. The increased temperature and rainfall in the early Holocene, decisive in the arboreal expansion process, was to cause an early decline in pine groves in the whole Iberian north-western area, which was more brusque and sudden in the more Atlantic zones of the Cantabrian mountain range. Deciduous taxa (headed by Quercus and/or Betula) found that this temperate climate was an advantage that allowed them to successfully compete against the conifer formations dominant in the Late-Glacial, displacing them in many areas. The pine groves, however, remained in different places but, above all, on the more continental, dry interior southern slopes. Nevertheless, various factors incline one to think that climate was not the only factor responsible for the generalised retraction of pine groves in the Holocene. Although the mass inertia with long-lived specimens already established in the area would confer a wide margin for maintaining those formations, the concurrence of fires, of either anthropogenic or climatic origin, could trigger processes which destabilised the competitive states in favour of resprouters. In addition to fire, or associated with it, anthropogenic elimination of woods and a simultaneous increase in grazing could be added to the factors responsible for decreasing the recolonising capacity of the surviving pines.