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ABSTRACT In this study we analyzed runoff and sediment yield from land under various traditional and current land uses in Mediterranean mountain areas, using long-term data from an experimental station in the Aísa Valley, Central Spanish Pyrenees. Monitoring at this station has provided 20 years of data that can help explain the hydrological and geomorphological changes that have been observed at larger spatial scales, and also the changes that have occurred to some of the most characteristic landscapes of the Mediterranean middle mountains. In spite of the problems associated with the use of small experimental plots, the results obtained are consistent with other studies in the Mediterranean region, and confirm the strong influence of land use changes on runoff generation and sediment yield. The results indicate that: (i) cereal cultivation on steep slopes (both alternating cereal cultivation and fallow on sloping fields and shifting agriculture on the steepest slopes) represents a major problem for soil conservation. This explains the occurrence throughout the Mediterranean mountains of many degraded hillslopes, which show evidence of sheet wash erosion, rilling, gullying and shallow landsliding; (ii) farmland abandonment has led to a marked reduction in runoff and sediment yield as a consequence of rapid plant recolonization, particularly by dense shrubs; (iii) the natural transformation of abandoned fields into grazing meadows has reduced runoff and sediment yield. Land use trends in the Mediterranean mountains are mainly characterized by generalized farmland abandonment and a decrease in livestock pressure. From a hydrological and geomorphological point of view the main consequences have been a reduction in overland flow from the hillslopes, and a reduction in sediment sources, with differences up to one order of magnitude in sediment yield from dense shrub cover and grazing meadow areas compared with areas under shifting agriculture. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Land degradation and soil erosion are key environmental problems in Mediterranean mountains characterized by both a long history of human occupation, and strong seasonality of hydrological regimes. Experimental monitored catchments have identified main controlling factors on erosion dynamics, but because of the short time span of the instrumental measurements they do not integrate the complete temporal and spatial variability of these environments. To obtain some long-term series of Mediterranean landscape evolution we propose a novel strategy based on multi-proxy analyses of lake sediments aimed to quantify sediment delivery and erosion dynamics. Karstic lakes in the Iberian Range (Central Spain) provide an opportunity to reconstruct the depositional evolution of the watersheds and to evaluate the response to both, the variable anthropogenic impacts and climate forcings during the last 1000 years. The most significant periods of increased sediment delivery (26–483 T km yr − 1 ) in the Iberian Range sites took place during the 15th–16th and 18th–19th centuries as a result of large land use changes and land clearing. Positive synergies between increasing human population and more humid periods led to peaks in sediment deliver during some phases of the Little Ice Age. Recent changes associated with the rural exodus and land abandonment during mid-20th century are more clearly shown in larger watersheds by decreased sediment delivery to the lakes due to the re-vegetation of the landscape (6–200 T km yr − 1 ). This new integrated approach based on long-term lake sequences provides a longer perspective of erosion processes in Mediterranean watersheds and validates the main factors identified in monitoring surveys (land cover and surface formations erodibility). In both settings, lakes and experimental catchments, most sediment delivery occurs during flooding events. Measured and reconstructed values show comparable large ranges, underlying the punctuated nature of sediment dynamics in Mediterranean landscapes at decadal and centennial scales. [ABSTRACT FROM AUTHOR]