/ Plant succession and pasture resources have been studied in abandoned fields of the central Spanish Pyrenees, in an environment severely affected by strong demographic pressure in the past. Several hydromorphological features (runoff and sediment yield) were also analyzed for different environments of the abandoned fields, in order to forecast the effects of their reclamation and transformation into areas for livestock use. The availability and accessibility of pastures as well as soil and water conservation is related to the process of colonization of Genista scorpius. Under a dense shrub cover both runoff and sediment yield are strongly controlled. As the shrub cover becomes open, sediment yield and runoff increase greatly. A dense herbaceous cover yields high runoff coefficients but moderate soil losses. From the results obtained, the possibility of abandoned field reclamation by means of selective clearing of scrub is discussed.KEY WORDS: Abandoned fields; Plant succession; Degraded environments; Soil erosion; Runoff; Spanish Pyrenees