**1. Introduction**

58 Soil Erosion Studies

Verburg, P.H.; Schulp, C.J.E.; Witte, N. & Veldkamp, A. (2006). Downscaling of land use

Xanthopoulos, G. (1998). Forest fires in Greece. Past, present and future. *Epikentra*, pp. 62-71

Zagas, Th.; Tsitsoni, Th.; Ganatsas, P. & Chatzistathis, A. (2004). Impacts of forest fires on

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(in greek)

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forest vegetation. Proceedings of the 8th National Conference of the Greek Forestry

According to the CORINE programme, Spain and Portugal are the Mediterranean countries in the European Union facing the greatest risk of erosion (Desir & Marín, 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; García-Ruiz et al., 1995, 1996; Nunes et al., 2010, 2011; Nunes, 2007; Pardini et al., 2002, 2003; Romero-Díaz, 2003; Ruiz-Flaño 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

Soil Erosion Under Different Land Use and Cover Types in a Marginal Area of Portugal 61

shallow soils, classified as distric cambisols (FAO-UNESCO, 1974), and an undulating relief with elevation ranges from 700 to 900 m a.s.l. The area has a sub-humid Mediterranean climate, characterised by wet, cool winters (5.8 ºC average temperature) and hot, dry summers (25.8 ºC average temperature). The mean annual precipitation of 800 mm has a high inter- annual variable distribution and seasonal concentration. The wettest periods of the year are concentrated in the autumn and winter months, between October and February,

Agricultural activities dominated land use in marginal areas of Portugal for many decades. In the 1960s, approximately over half the utilized agricultural area was divided between nonirrigated cereals (the dry system) and unseeded fallow rotations. Cereal crops were sown from October to mid November to make use of autumn precipitation for germination. Spring was the main growing season and mature cereals were harvested in June to early July before the onset of the hot, dry months. Cereal fields were rotated with unseeded fallow in order to

Agricultural activities have become less important since the mid-20th century, coincided with the widespread migration of the population to certain European countries (France,

regenerate soil moisture and nitrogen levels for the following year's cereal rotation.

and the driest in summer, between June and September.

Fig. 1. Location of the study area

the Portuguese Utilised Agricultural Area (UAA) falls within the definition of Less Favoured Areas (LFAs), and a substantial amount of this is classified as mountain area. Much of this mountain zone is designated Objective 1.

In 1992, measures accompanying the reform of the Common Agricultural Policy (CAP) were adopted to benefit the environment, early retirement and forestry. These measures aimed to support the envisaged processes of change, and to mitigate some of the effects deemed to be disadvantageous to farmers (Van-Camp et al., 2004). European Economic Commission (EEC) Regulation 1765/92 (EEC, 1992) led to a substantial increase in set-aside land in the European cereal-growing regions (Crabb et al., 1998; Van Rompaey et al., 2001). Agricultural land afforestation (Regulation 2080/92), which established an aid programme for the afforestation of former agricultural lands, also aimed to enhance long-term forest resources and combat soil erosion and desertification by promoting forestry as an alternative form of land use. However, the overall effectiveness of afforestation in reducing soil erosion remains uncertain, due to the poor development of the forest cover in some areas leading to significant areas with sparse tree cover, and the erosional impact of forest harvesting, which usually involves clearcutting (Porto et al., 2009). In fact, little data is available. The extent to which these measures are applied in areas under medium/high risk of soil erosion needs to be assessed (Van-Camp et al., 2004).

According to Caraveli (2000), the implementation of CAP measures in Mediterranean countries has reinforced *intensi*fi*cation* processes in productive practices in the more fertile areas of the lowlands and *extensi*fi*cation* (i.e. abandonment or marginalisation and the collapse of traditional farming systems) in the LFAs, which has been going on for decades. Land use changes characteristic of extensification include fewer cultivated fields, more shrub patches, larger areas of natural pastures, and abandonment of some patches, followed by the development of stratified bush communities. The CAP agreement requires Member States to maintain a permanent pasture area, which should prevent the wide-scale ploughing up of land for arable cultivation and potential problems with soil degradation often associated with arable farming in some areas (Van-Camp et al., 2004). Nevertheless, the influence of grazing on vegetation development and soil erosion processes is rarely quantified in literature on the subject (Ries, 2010).

The specific objectives of the current research were: (i) to evaluate and compare the hydrological and erosional response of soils under different land uses and vegetation types in central inland Portugal, (ii) to identify and describe the main factors that control their hydrogeomorphic response and (iii) to assess the efficiency of alternative land uses proposed by the CAP for soil erosion control. The six land uses and vegetation types studied (cereal crop, fallow land or short-term abandonment, shrub land or long-term abandonment, recovering autochthonous vegetation or very long-term abandonment, arable land afforested with *Pinus pinaster* and arable land transformed into pastureland) are representative of situations frequently found throughout central and northern Portugal, and also in other Mediterranean systems. The main aim was to obtain consistent conclusions for ecosystem management in marginal areas of Portugal. This information on the hydrogeomorphic response could be useful in the future as a guide for regional soil conservation planning.
