La evolución del piso subalpino en la Sierra de Urbión (Sistema ibérico, norte de España): un modelo de impacto geoecológico de actividades humanas en el Valle de Ormazal

Abstract

This paper is a synthesis of the landscape, geomorphic and functional evolution of the subalpine belt in the Urbion Sierra, providing a geoecological perspective of the interactions between human activity, spatial organization, geomorphological dynamics and recent land use changes. Landscape changes in the subalpine belt started at least during the Late Neolithic, with forest fires that tried to waste the forest to enable the expansion of summer grasslands favouring an incipient sheep transhumance. Fires occurred also through the Chalcolithic and the Bronze and Iron Ages, and culminated during the Middle Ages. Deforestation of the subalpine belt would be responsible for the triggering of a number of shallow landslides and soil erosion in steep slopes above 1500 m a.s.l. The crisis of the transhumance since the beginning of the 19th century reduced the livestock pressure, particularly in the second half of the 20th century, and has contributed to shrub and forest expansion, whereas the area occupied by summer grasslands has been remarkably reduced. The decreasing livestock pressure suggests that forest expansion will continue in the next future, in a favourable context of global warming and declining presence of snowpack in the subalpine belt.