Soil properties and physiographic factors controlling the natural vegetation re-growth in a disturbed catchment of the Central Spanish Pyrenees

Large changes in land use have occurred in the Central Spanish Pyrenees during the twentieth century. This mountain area supported an intense human use since the Middle Ages, that greatly transformed the natural landscape. The land uses changed dramatically during the first half of the twentieth century, due to major socioeconomic forces which lead to depopulation and land abandonment. Since then, a process of natural vegetation recovery has taken place. The anthropogenic impact during centuries deteriorated the soil quality, threatening the sustainability of agroecosystems and the natural vegetation re-growth. In this study, a soil survey was performed to identify the soil types and the physico-chemical properties of the soil that are relevant for maintaining the soil function for the recovery of vegetation after land abandonment. The study was conducted in the Arnas River catchment, which is representative of the region. The highest cation exchange capacity (CEC), nutrients, water retention, water availability and infiltration rates, as well as the lowest pH and carbonates, occurred in Lithic Hapludolls and Calcic Haploxerolls at the shady aspect, under a forest cover. Lithic Ustochrepts and Lithic Xerorthents on the sunny aspect, which were covered by shrubs, were of lesser quality than were the deeper and better-developed soils on the shady aspect. This is seen as an evidence of different patterns of soil degradation, which conditioned the re-growth of natural vegetation after land abandonment. The results provide insights into the main soil factors that have affected the re-establishment of natural vegetation in recent years. Recommendations are given for designing effective strategies for soil conservation after land abandonment in similar mountain environments.