**2. Study area**

The study was carried out in the high Côa river catchment, in a peripheral area of Portugal close to the Spanish border (Fig. 1). The substratum comprises mainly granites with poor, 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, and the driest in summer, between June and September.

Fig. 1. Location of the study area

60 Soil Erosion Studies

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.

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

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

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

The study was carried out in the high Côa river catchment, in a peripheral area of Portugal close to the Spanish border (Fig. 1). The substratum comprises mainly granites with poor,

Much of this mountain zone is designated Objective 1.

be assessed (Van-Camp et al., 2004).

conservation planning.

**2. Study area**

quantified in literature on the subject (Ries, 2010).

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

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

Soil Erosion Under Different Land Use and Cover Types in a Marginal Area of Portugal 63

The 1992 MacSharry reforms to the European Union Common Agricultural Policy have reinforced the falling rates of cereal production. The reforms included a set-aside program requiring farmers to take certain percentages of their arable land out of production. With the opening up of international markets and the lowering of crop prices, the market-oriented cultivation of cereals became unprofitable in most of Portugal. Farmers receive more in the form of direct payments per hectare under the set-aside regime in comparison with arable crop production. Consequently, they put greater percentages of their farms into set-aside. As an example, in the Guarda district early retirement has affected about 10 000 farmers and an area between 60 000 ha and 90 000 ha, since 1996. This represents about 40% of the total

In contrast, pastureland has increased by over 25%, in the last two decades (INE, 2000). In fact, recent EU agri-environmental measures support the maintenance of natural pastures or the extensive cultivation of fodder crops (without deep ploughing and the use of fertilisers) and the livestock unit subsidy supports maintenance of livestock (Borges et al., 1997). The current CAP measures for Portugal also promote forest development measures (EU

Six types of land use associated with traditional land use, land abandonment and subsequent plant recovery, and alternative land uses proposed by the CAP for marginal areas (extensification of land use and conversion of arable land to forest) were selected for

In dry cereal systems with Mediterranean marginal soils, during March/April the 20-30 cm of top soil is turned over and remains without vegetation until sowing. This process is called laying fallow. The cereals are planted from October to mid November to make use of autumn precipitation for germination. Spring is the main growing season and mature

In a rainfed cereal system, fallow land is a traditional part of the cereal rotation system. During fallow cycles, land remains unseeded for 2, 3 or more years to enhance soil fertility and soil moisture availability for subsequent crops. No chemical fertilizers or manures are used, and the plant residue is kept in the fields. Fallow lands are usually used as grazing land

When arable land is abandoned, a process of plant colonisation begins. This is a very complex process in which ecological conditions (both physical and biotic factors), human activity (the agricultural history of the fields' as well subsequent management, namely grazing, fire, clearing, etc.) and time interact. Before shrubby species, mainly *Cytisus spp.,*  proliferate, abandoned fields in central inland Portugal are invaded by herbaceous plants during the first years of abandonment. It can take more than 15-20 years for shrub land with a high percentage of ground cover to develop. Due to the accumulation of biomass in

The Pyrenean oak (*Quercus pyrenaica* willd.) is the autochthonous species in this area. Human activities over the centuries have led to considerable deterioration of the native arboreal

cereals are harvested from June to early July before the onset of the hot, dry months.

2. Fallow land (traditional land use or short-term abandonment)

in traditional land use agropastoral herding practices in the territory.

abandoned fields after recolonisation, there has been an increase in forest fires.

number of farmers and 30%-45% of the utilised agricultural area.

Regulation 2080) by supporting new plantations and shrub clearance.

**3. Methodology** 

1. Cereal crops (traditional land use)

3. Shrub land (long-term abandonment)

4. Recovering oak (very long-term abandonment)

the study.

Germany, Luxembourg, etc.) and to urban centres (Nunes, 2007). This exodus and subsequent abandonment of cultivated land was associated with the low rate of return from traditional crops, a result of the low productivity of dry farming systems (a Mediterranean climate, undulating relief, and poor, shallow soils), uncompetitive farm structures (with small, scattered plots), the peripheral location of the area, the lack of alternative employment sectors and the extensive presence of elderly farm owners. Furthermore, the socio-economic and political changes in Portugal in the 1970s that led to higher agricultural wages and migration from the countryside, made it difficult to maintain traditional management and manual shrub clearing, which was essentially based on low labour costs. During the period 1960-2001, the study area lost about 60% of its total population and more than 90% of its farmers.

According to SROA (Service of Agrarian Recognition and Management, 1951-56) statistics, in the middle of the last century cereal cultivation occupied about 55% of the total area of the Guarda district. Five decades later, the same crop only represented 10% of the total surface (CORINE Land Cover, 2000), meaning that approximately 80% of the cereal crop area had been abandoned.

Complete farm abandonment has resulted in enhanced natural secondary succession and the spread of shrub and woodland (Lasanta et al., 2009). In the first stage of land abandonment, after 4-5 years the dominant vegetation belongs mainly to the *Gramineae* family and forms a sparse herbaceous cover (Fig. 2). Perennial shrub communities, mainly dominated by nanophanerophytes such *Cytisus multiflorus* and *Lavandula sampaioana*, follow after two decades of farmland abandonment. As a result of the abandonment of cultivated land and the decline in forest land, shrub plant communities have become one of the most important vegetation types in the Iberian Peninsula (Casermeiro et al., 2004). Negligible areas are covered by recovering *Quercus pyrenaica*, indicating a lengthy period of abandonment of approximately 30-40 years. The *Quercus pyrenaica Willd*. wood is the characteristic autochthonous vegetation in the study area. The unmanaged accumulation of large quantities of fuel has led to a dramatic increase in forest fires and burnt areas (Carvalho et al. 2002), and therefore to difficulties with *Quercus* regeneration.

Fig. 2. Dynamic evolution of vegetation in the study area following land abandonment (adapted from Capelo, in Costa et al., 1998)

The 1992 MacSharry reforms to the European Union Common Agricultural Policy have reinforced the falling rates of cereal production. The reforms included a set-aside program requiring farmers to take certain percentages of their arable land out of production. With the opening up of international markets and the lowering of crop prices, the market-oriented cultivation of cereals became unprofitable in most of Portugal. Farmers receive more in the form of direct payments per hectare under the set-aside regime in comparison with arable crop production. Consequently, they put greater percentages of their farms into set-aside. As an example, in the Guarda district early retirement has affected about 10 000 farmers and an area between 60 000 ha and 90 000 ha, since 1996. This represents about 40% of the total number of farmers and 30%-45% of the utilised agricultural area.

In contrast, pastureland has increased by over 25%, in the last two decades (INE, 2000). In fact, recent EU agri-environmental measures support the maintenance of natural pastures or the extensive cultivation of fodder crops (without deep ploughing and the use of fertilisers) and the livestock unit subsidy supports maintenance of livestock (Borges et al., 1997). The current CAP measures for Portugal also promote forest development measures (EU Regulation 2080) by supporting new plantations and shrub clearance.
