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Semiarid lands have been affected by intense afforestations since the end of the 20th century. Plantations were developed to control soil and water losses, prevent flooding, reduce check dams silting and, since the 1970s. to fight against desertification. The afforestations in semiarid environments were and are developed by means of aggressive techniques, employing heavy machinery and landform changes. In the Region of Murcia. South eastern Spain, studies have been carried out for the last three decades in afforested areas mainly on marls, conglomerates and schists. Sub-soiling has been used in order to transform the straight slopes into a terraced man-made landscape. Geomorphological transects, topographic profiles and erosion plots have been used to quantify the erosion rates on afforested and non-afforested areas. The results show an increase in water erosion as a consequence of afforestation. Soil erosion rates were 105 Mg ha(-1) y(-1) in marls, 63 Mg ha(-1) y(-1) in conglomerates and 29 Mg ha(-1) y(-1) in schists, where rills and gullies were widespread. Soil erosion rates were lower than 2 Mg ha(-1) y(-1) on the control plots (in all parent materials) due to the scrubland cover. Afforestations contributed in increasing soil losses between I and 2 orders of magnitude. However, the regional, national and European governments are planning to invest in new afforestation programmes. Copyright (C) 2009 John Wiley & Sons, Ltd.