/ 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
In the tropical Andean environments little is known about the relationship between weed dispersal and disturbances caused by cattle. We propose that abundance and dispersal of the Venezuelan Andean weed Acaena (Acaena elongata L.) is associated with the widespread grazing habits of cattle. We stu&ed Acaena presence in areas with different cattle movements and grazing intensities. Acaena density increased with cattle trail density (fl q .98,P<.OOl). Infestation patterns suggested dispersal by cattle along trails. Areas with greater cattle movement (0.34 trails/m) possessed the greatest density and highest number of Acaena plants (P<.OOl). This weed has morphological and phenological features adapted to cattle dispersal. Fruits mature during the season when cattle are less selective and travel the greatest distances.
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