Natural regeneration of degraded soils and site changes on abandoned agricultural terraces in Mediterranean Spain

Abandonment of degraded and marginal agricultural land is a widespread phenomenon in Spain and other Mediterranean countries. To study soil development and site dynamics, a comparative investigation of field groups representing different ages of abandonment was realized in the Meastrazgo region of the Mediterranean province of Castellón. Analysis of soil samples for organic carbon and total nitrogen content and pH showed that a sufficient regeneration of organic matter is accomplished after 20 years of fallow. Contrary to this there is no build-up of ‘available’ phosphorus after abandonment. A fixation of phosphorus in unavailable forms in the first fallow years seems evident, and there is no re-enrichment through solution or mineralization of organically bound P thereafter. The vegetation of the fallow fields develops after passing through a low-cover therophyte stage within 10–20 years to nanophanerophyte-dominated matorral (shrubs), in the best case within 40–50 years to a stone oak juniper association. Under intensive cattle grazing, grasslands rich in hemicryptophytes evolved. Rates of soil erosion estimated through application of the Universal Soil Loss Equation are of medium to low intensity and range between 2·2 t ha−1 year−1 in the first fallow years and 0·6 t ha−1 year−1 after establishment of vegetation cover. Under grassland erosion is negligible unless vegetative cover is destroyed through treading.