METHODOLOGIES FOR SOIL EROSION AND LAND DEGRADATION ASSESSMENT IN MEDITERRANEAN-TYPE ECOSYSTEMS

The detection of spatial distribution and temporal development of soil erosion processes and forms on abandoned land still represents a great scientific challenge. Abandoned fields as a result of land use changes during the past century can frequently be found in the Mediterranean. The former fields are generally used for grazing and therefore are highly complex concerning the variability of soil erosion processes. A three-step research method is used for assessment and evaluation of soil erosion processes. By means of rainfall simulations, test plot monitoring and large-scale aerial photography, erosion processes are quantified and scenarios are presented for three test sites M northeast Spain. With a large-scale test plot monitoring the development of soil erosion processes can be evaluated. Areas with predominantly increasing soil erosion activity are classified as unstable, whereas areas with unchanged or decreasing soil erosion activity are classified as vulnerable or stable. Forty to 70 years after abandonment and change to grazing all observed test areas show a progressive degradation. The proportion of unstable areas reaches around 50 per cent. The extension of unstable areas, characterised by a combination of increasing erosion activity and decreasing vegetation cover, is highest within the semi-arid Ebro Basin reaching 29 per cent of the whole area. Dense vegetation cover does not always correlate with stability in erosion and increase in cover does not generally lead to a stabilisation of erosion processes. Even under increasing vegetation cover of more than 60 per cent high erosion and runoff rates are possible particularly in connected rills and on sheep trails. Therefore, grazing on abandoned fields is the critical factor leading to further degradation. Copyright (C) 2009 John Wiley & Sons. Ltd.