An Ice Age island in the mountains
During the last glacial period, which peaked around 20,000 years ago, vast ice sheets covered much of northern Europe. In Spain, the Picos de Europa mountains was an important sanctuary, or "glacial refugium." This limestone massif, rising to over 2,600 meters, was not completely buried by a monolithic ice cap. Instead, its steep-sided topography and porous karst geology created a mosaic of exposed peaks (nunataks) and ice-free valleys where life could persist. The interaction of glaciation and the water-soluble limestone created a unique area of deep gorges, sinkholes (called jous), and underground cave systems, some of the deepest in Europe. This geological complexity provided microclimates, allowing species to survive the harsh glacial conditions just kilometers from advancing valley glaciers. The maximum glacial extent here occurred even before the global peak, prior to 35,000 years ago.
Living laboratories of evolution
The isolation imposed by the surrounding ice left a genetic signature on the region's flora. Many plant species endemic to the Picos de Europa and the wider Cantabrian Mountains evolved in this refuge. Examples include the bellflowers Campanula arvatica and Campanula cantabrica, and the houseleek Sempervivum vicentei subsp. cantabricum. Genetic analysis of alpine plant populations shows deep divergence from their relatives in the Pyrenees, separated by only a short distance. This physical barrier of ice, now long gone, was a powerful engine of evolution, leading to the formation of new subspecies.
The Picos de Europa also was a haven for fauna. The Cantabrian brown bear (Ursus arctos), a genetically distinct population, lives in these mountains. While the genetics of post-glacial colonization are complex, with evidence suggesting some populations were later replaced by bears from other refugia, the mountains were a clear area of Pleistocene survival. Another important species is the Cantabrian capercaillie (Tetrao urogallus cantabricus), an endangered grouse subspecies that is from the ice ages. The ancient beech (Fagus sylvatica) and oak (Quercus robur) forests that shelter these animals are part of this long history of survival.