Geomorphic and Hydrological Effects of Traditional Shifting Agriculture in a Mediterranean Mountain Area, Central Spanish Pyrenees

Abstract

Shifting agriculture has been practiced over large areas in middle-latitude mountains in the Mediterranean basin during periods of strong demographic pressure. On average, such land accounted for about 22.8% of the total cultivated area in the Central Spanish Pyrenees at the beginning of the 20th century. The use of experimental plots between 1992 and 2003 demonstrated that shifting agriculture increased overland flow, suspended sediment, and solute concentration. Total soil loss was about 14 times higher on plots under shifting agriculture than on plots under dense shrub cover, and almost 3 times higher than on permanent sloping fields. Erosion rates ranged between 0.1 and 1.4 t/ha/yr. The abandonment of shifting agriculture practices resulted in rapid plant recolonization and a decrease in runoff and soil erosion. Nevertheless, severe geomorphic processes were found to be still active several decades after abandonment, explaining landscape degradation and the occurrence of shallow landslides.