Soil Erosion Under Different Land Use and Cover Types in a Marginal Area of Portugal

Abstract

According to the CORINE programme, Spain and Portugal are the Mediterranean countries in the European Union facing the greatest risk of erosion (Desir & Marin, 2007). In Portugal, areas at high risk of erosion cover almost one third of the country (Grimm et al., 2002). The main causes of soil erosion are inappropriate agricultural practices, land abandonment, deforestation, overgrazing, forest fires and construction activities (Grimm et al., 2002; Yassoglou et al., 1998). Several studies in the Mediterranean region have addressed the present-day hydrological response and erosion rates for arable and marginal land affected by land abandonment (Casermeiro et al., 2004; Garcia-Ruiz et al., 1995, 1996; Nunes et al., 2010, 2011; Nunes, 2007; Pardini et al., 2002, 2003; Romero-Diaz, 2003; Ruiz-Flano et al., 1992), forest fires (Cammeraat & Imeson, 1999; Coelho et al., 2002, 2004; Doerr et al., 2000; Ferreira et al., 2005; Ferreira, 1990; Ferreira, 1996; Imeson et al., 1992; Shakesby et al., 1993, 1996) and afforestation (Ferreira, 1996; Ternan et al., 1997; Thomas et al., 2000; Shakesby et al., 2002). The results show wide variations in runoff generation and sediment yield, mainly depending on environmental conditions, vegetation cover, changes in previous land use, the period of soil abandonment, etc. In Portugal, as well as in many other Mediterranean countries, the main type of land use was rainfed cereal crops until the middle of the twentieth century. After the introduction of modern agriculture, the opening up of the international markets and the lowering of crop prices, market-oriented cultivation of cereals became unprofitable in most marginal areas in Portugal. In addition, socio-economic and political changes in Portugal in the 1970s led to higher agricultural wages and migration from the countryside (Pinto-Correia & Mascarenhas, 1999). Thus, abandoned farmlands became evident, very often in marginal, mountainous or semi-mountainous areas and areas that were difficult to access, in which traditional or semi-traditional agriculture was practised until recent decades, involving low input and intensive human labour. Abandonment implied the extensive decline of arable land and resulted in very important transformations to the landscape, characterised by the spread of natural vegetation, including both shrub land and forest. Additionally, the EU’s Common Agricultural Policy recognises the natural handicaps of such areas and their association with depopulation and land abandonment through its structural support for ‘Less-Favoured Areas’ (Regulation 950/97). Around eighty per cent of