hydrological and erosive consequences of farmland abandonment in europe

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HYDROLOGICAL AND EROSIVE CONSEQUENCES OF
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2 FARMLAND ABANDONMENT IN
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4 EUROPE –A REVIEW
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8 José M. García-Ruiz (1) and Noemí Lana-Renault (1, 2)
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(1) Instituto Pirenaico de Ecología, CSIC, Campus de Aula Dei, Apartado 13.034,
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50080-Zaragoza, Spain. E-mail: [email protected]
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15 (2) Department of Physical Geography, Utrecht University, Faculty of Geosciences,
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17 P.O. Box 80115, Utrecht, The Netherlands. E-mail: [email protected]
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Abstract
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Farmland abandonment is a major problem in parts of Europe, particularly in
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mountain areas and semiarid environments. In such places, farmland abandonment
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26 represents a significant land use change from cropping to a complex of plant
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28 successions. The present study assesses the hydromorphological effects of land
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30 abandonment in Europe, and the consequences thereof with respect to water resource
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availability and soil erosion. The evolution of abandoned fields depends on (i) the time
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of abandonment; (ii) climatic conditions in the abandoned area; (iii) particular
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characteristics of the fields; (iv) the land management regimen following abandonment;
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37 and, (v) the role played by government policy. Throughout most of Europe, vegetation
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39 on abandoned farmland has evolved into dense forest or shrub. The expansion of
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41 vegetation explains, in part, the perceived decline in water resources, reductions in soil
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loss and sediment delivery, and the progressive improvement of soil characteristics.
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Such evolution has resulted in changing stream morphology, featuring narrowing and
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incision, and a decline in sedimentation level in Mediterranean reservoirs. The
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48 abandonment of bench terrace fields coincided with an increase in the occurrence of
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50 small landslides in the steps between terraces, as well as changes in the spatial
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52 organization of saturated areas. Plant colonization is slower in semiarid areas,
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increasing the development of soil crusts that reduce infiltration and increase overland
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flow. Land policies with detailed capability are necessary to remediate the consequences
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57 of farmland abandonment in various European environments.
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Key words: farmland abandonment, runoff generation, soil erosion, bench terrace
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fields, semiarid areas, Europe
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3

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5 1. Introduction
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7 Land use change is the main characteristic of rural areas in Europe during the
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9 20th century (Cernusca et al., 1996; Debussche et al., 1999; Rabbinge and Van Diepen,
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2000; Taillefumier and Piégay, 2003; Palang et al., 2005; Rounsevell et al., 2006;
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García-Ruiz, 2010). This occurred because of (i) changes in population density in rural
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areas, mainly attributable to migration to the cities; (ii) development of mechanization
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16 and novel agricultural techniques; (iii) low productivity in some rural areas (Duarte et
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18 al., 2008); (iv) regional, national, and international market forces; (v) an increasing
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20 effect of regional and national governmental initiatives, which subsidize some crops to
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the detriment of others, and have financed very expensive infrastructure including
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reservoirs and canals; (vi) effects of the Common Agricultural Policy (CAP) (Lasanta et
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25 al., 2000; Boellstorff and Benito, 2005); and, (vii) socioeconomic and political factors,
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27 including marked transformations of rural landscapes in post-communist eastern Europe
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29 (Kuemmerle et al., 2008). The agrarian landscapes of Europe have changed
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31 dramatically, particularly with respect to plot size; the types of crops planted; and the
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relative spatial distributions of fields, shrubs and forests. Today, these parameters bear
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34 little resemblance to those pertaining at the beginning of the 20th century.
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36 These observations are particularly valid for mountainous and certain semiarid
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38 regions of Europe, where the characteristics of past landscapes are now almost
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40 unrecognizable, particularly because of the large expansion of regions characterized by
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farmland abandonment. In mountainous areas, physical constraints together with
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population ageing and small farm sizes have reduced competitiveness (Ruiz-Flaño,
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1993; MacDonald et al., 2000), and farmland abandonment has thus occurred despite
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47 centuries of intensive human use of steep slopes. In semiarid areas, abandonment has
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49 resulted in declining productivity following continued cultivation of poor soils, and,
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51 more recently, CAP implementation, which has enhanced withdrawal of land from
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cultivation.
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Farmland abandonment occurred throughout Europe during the second half of the
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56 19th century, as a consequence of population movements from mountains to the cities.
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58 This was initially evident in the most industrialized countries (the United Kingdom,
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60 Germany, the Netherlands, Belgium, Switzerland, and France), next in Italy, and finally
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in Spain, Portugal, the Balkans, and the Carpathians. Lowland areas were also affected
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by depopulation, but farmland abandonment was not immediately evident because
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individual farm sizes increased as farms were amalgamated. In semiarid areas, farmland
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5 abandonment has been relatively recent, associated not with population movements, but
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7 rather with problems of water scarcity and the low soil quality of large flat fields (Oñate
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9 and Peco, 2005). It is noteworthy that land abandonment can co-exist with
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intensification of land use (Douglas et al., 1994; Van Eetvelde and Antrop, 2004;
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Mottet et al., 2006; Chauchard et al., 2007). This has occurred in some mountainous
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areas, where slopes have been increasingly subjected to abandonment although valley
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16 bottom cultivation has intensified, featuring the use of meadows for production of
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18 livestock feed and the construction of agricultural buildings and other infrastructure.
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20 Two types of farmland abandonment can be distinguished in Europe. The first is a
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form of spontaneous abandonment affecting all European mountain areas, driven by
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either a progressive or sudden collapse of mountain societies. This process, which has
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25 occurred in the Pyrenees, resulted in restriction of cultivation to valley bottoms and
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27 some smooth hillslopes, with little agricultural effort being devoted to mountainous
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29 areas (Lasanta, 1988, 1989). This process also affected some semiarid areas in southeast
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31 Spain, as a consequence of soil deterioration following irrigation in the 1970s, and the
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progressive scarcity of water resources. Induced abandonment, prescribed by national or
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European Community policies designed to regulate markets for particular agricultural
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36 products (Baudry, 1991), has also been important. Such abandonment has been
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38 controlled by the CAP, and affects only some agricultural land, mainly in plains and
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40 piedmonts. The CAP has encouraged the withdrawal (termed “set-aside”) of cultivated
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land, to reduce food surpluses and to limit the huge cost of agricultural subsidies under
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European Union commitments. Farmers that produce more than 92 tonnes of cereal per
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year are obligated to cease cultivation on part of their property, although the portion set
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47 aside can vary from year to year, in both rainfed and irrigated areas (Walford, 2002).
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49 Farmers can designate withdrawn land as unseeded or seeded fallow (Boellstorff and
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51 Benito, 2005). Unseeded fallow land is most common in semiarid regions, where soil
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moisture is a major factor limiting crop productivity. Seeded fallow is more common in
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relatively humid temperate areas, where the fields are planted with grasses or
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leguminous plants for at least 1 year after a cereal harvest. In both instances, the
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58 objective is to improve soil humidity, fertility, and organic matter content. Seeded
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60 fallow efficiently protects soil against erosion.
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Farmland abandonment is an important cause of changes in landscape and wildlife
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communities, and has resulted in a loss of biodiversity (MacDonald et al., 2000) and
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lower levels of open areas. Environmentally, the most obvious consequence of land
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5 abandonment is plant recolonization. Regardless of abandonment type, a more- or-less
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7 complex plant colonization process occurs on abandoned fields, conditioned by soil and
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9 climate characteristics. Several years after abandonment, such fields are covered by
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grasses, shrubs, and trees. In many European regions, forests cover slopes that were
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under cultivation some decades ago, and this process has been accompanied by
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substantial environmental changes. Farmland abandonment during periods of social
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16 upheaval (e.g., during the Black Death; AD 13471352) and war has been well-
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18 documented (Yeloff and Van Geel, 2007), and such events have been associated with
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20 expansion of forests (mainly of Betula and Corylus trees), based on results obtained
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from pollen records.
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The hydrological and geomorphological effects of farmland abandonment and the
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consequent changes in land cover have been extensively examined, particularly in the
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27 Mediterranean region (Llorens et al., 1992, 1997a; Ruiz Flaño et al., 1992; Ruiz-Flaño,
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29 1993; Gallart et al., 1994; Cerdà, 1997; Lasanta et al., 2000, 2006; Piégay et al., 2004;
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31 Cammeraat et al., 2005; Koulouri and Giourga, 2007; Lesschen et al., 2007, 2008;
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Romero-Díaz et al., 2007; Bakker et al., 2008; López-Moreno et al., 2008; Seeger and
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Ries, 2008; Nunes et al., 2010). Key issues related to land abandonment in Spain,
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Portugal, and France include the effects of such action on (i) soil hydrology, (ii) runoff
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38 generation, (iii) the extent of areas contributing to runoff, (iv) the nature of sediment
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40 sources, (v) soil erosion and evolution thereof after land abandonment, and, (vi) fluvial
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42 channel adjustments. These issues are particularly important in Europe, and especially
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in the Mediterranean region, where water resources are sourced almost exclusively from
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mountain headwaters, which behave either as water towers (Vivirioli et al., 2003, 2007)
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or as humid islands surrounded by subhumid or semiarid lands. The scarcity of water
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49 resources and spatial and temporal variabilities of discharge have necessitated the
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51 introduction of complex water management procedures, including construction of large
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53 reservoirs. Consequently, any land cover changes in mountains potentially threaten the
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delicate balance between water resource availability, reservoir management, ecological
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flows, and water use in lowlands. In particular, changes in plant cover will affect
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sediment sources and the connectivity between them and stream channels, which in turn
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60 will alter sediment yields, thus affecting reservoir silting and water quality.
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The present report reviews our current knowledge on the hydromorphological
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evolution of abandoned fields in various European environments. Our main objective is
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to identify the principal factors affecting water resources and soil erosion, through a
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5 comparison of different types of abandoned fields in mountainous and semiarid areas.
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9 2. The extent of farmland abandonment
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Farmland abandonment has not been random from either a temporal or spatial
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viewpoint (Lasanta, 1988, 1989; Ruiz-Flaño, 1993; Douglas et al., 1994; García-Ruiz et
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al., 1996a). Such abandonment initially affected countries that became industrialized in
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16 the 19th century. From the middle of that century, populations in mountainous areas of
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18 the United Kingdom, Germany, Switzerland, northern Italy, and France migrated
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20 extensively to the cities, thus reducing the pressure on cultivated lands (Walther, 1986).
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In these countries, the main episode of population migration, and hence farmland
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23 abandonment, was largely complete by the first decades of the 20th century. In
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25 Mediterranean countries, the principal period of industrialization and population
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27 migration occurred in the middle of the 20th century (in the 1960s and 1970s), although
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29 a decrease in population in agricultural areas was already evident at the beginning of the
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31 century, particularly in Spain and Italy. Thus, farmland abandonment in Mediterranean
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countries was quite prolonged (extending over 60-70 years).
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According to Lasanta (1988), Ruiz-Flaño (1993), and García-Ruiz et al. (1996b),
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36 field abandonment initially featured the steepest slopes of the highest areas, and both
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38 straight and convex slopes, particularly in regions remote from villages. In general,
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40 shifting agriculture fields were first abandoned because of marginal location and low
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productivity. Thereafter, abandonment affected both bench terraces and sloping fields,
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even those with relatively shallow gradients (10-20%). Abandonment was associated
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with difficulties in the use of modern agricultural machines on concave slopes and even
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47 on perched flats that were relatively distant from villages. Lasanta (1988) suggested that
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49 physical factors (altitude, exposure, and gradient) were the most influential in the first
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51 stages of abandonment, whereas, at later stages, human-related considerations (distance
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from a village, limited opportunities for mechanization) played a more decisive role. At
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present, only the valley bottoms in most European mountainous areas are cultivated, for
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example in the Alps, together with some shallow slopes cultivated with cutting
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58 meadows. Farmland abandonment was also significant in eastern European countries
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60 during the 1990s because of political changes that followed the fall of communist
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regimes. In semiarid regions, abandonment first affected non-irrigated rainfed fields
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with poor yields, and those degraded by irrigation (Romero-Díaz et al., 2007).
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Various studies have reported the relative extent of farmland abandonment
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5 throughout Europe. Figure 1 shows the spatial distribution of studies dealing directly or
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7 indirectly with the hydrological and geomorphological consequences of farmland
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9 abandonment (please see Table 1 also). The concentration of studies in the
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Mediterranean region (and Spain in particular) is noteworthy, as are the numerous
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reports on the Pyrenees, the Iberian Range, and the Mediterranean coast. France (the
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Prealps of Provence, the Central Massif), Italy, Portugal, Greece, and Slovenia have
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16 also been the focus of a range of studies. In the remainder of Europe, isolated reports
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18 have come from Belgium, Germany, Switzerland, Austria, Hungary, Latvia, and
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20 Estonia, and from the area between Poland, Ukraine, and Slovakia.
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Land abandonment in European Mediterranean countries is concentrated in
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mountainous areas and some semiarid regions, particularly in Spain and Portugal.
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25 Lasanta (1989), Ruiz-Flaño (1993), and Poyatos et al. (2003) reported abandonment of
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27 most fields on hillslopes in the Pyrenees and the Iberian Ranges. García-Ruiz et al.
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29 (1996a, b) noted that the maximum size of the farmed area in the Pyrenees was probably
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31 attained in the middle of the 19th century, which coincided with the greatest population
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density of the region. A period of land abandonment followed, which was directly
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attributable to migration (primarily between 1950 and 1970), the failure of cereal crops
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36 produced on mountain hillslopes to be economically competitive, and the limited
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38 opportunities available for using the new machinery that was elsewhere (in the valley
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40 bottoms) increasing productivity. Lasanta-Martínez et al. (2005) and Lasanta and
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Vicente-Serrano (2007) noted that abandoned fields represented 22% of the total area of
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the central Spanish Pyrenees. Poyatos et al. (2003) estimated that grasslands and crops
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represented 28.3% of the total area of the Cal Rodó catchment (eastern Pyrenees) in
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47 1957, but only 18.1% in 1996. In the same period, the area occupied by dense forests
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49 increased from 16.9% to 45.3%. Abandonment was also extensive in the southern
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51 Spanish mountains (the Betic Ranges), although many fields are still cultivated on
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relatively steep slopes (Faulkner, 1995). Land abandonment also progressed in semiarid
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areas of southeastern Spain (Romero-Díaz et al., 2007) and central-southern Portugal
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(Van Doorn and Bakker, 2007; Nunes et al., 2010) because of the low productivity of
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58 dry farming systems, where 1 year of cereal cultivation alternated with 2 or more years
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60 of fallow. In southern Portugal, the decrease in arable land resulted in a rise in
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afforestation, regeneration of montado open forests, and an expansion of shrub cover
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(Van Doorn and Bakker, 2007).
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In France, most marginal lands were abandoned in the Malay Massif (southern
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5 French Alps) after the middle of the 19th century, resulting in an expansion of shrubland
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7 and forests, and a decrease in semi-natural open habitats (Chauchard et al., 2007). In
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9 1842, forests covered 56% of the Plaine de Malay, but the plain is now entirely covered
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with Pinus sylvestris, Abies alba, and Fagus sylvatica forest. Land use changes since
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12 the first third of the 19th century have been described in the southern French Prealps.
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Taillefumier and Piégay (2003) noted that this area experienced a substantial increase in
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16 grassland (from 14% to 34.6%) between 1828 and 1956, and a large fall in the extent of
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18 ploughed land (from 36.4% to 12.1%). A marked expansion of forest (from 31.9% to
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20 51.2%) and shrub areas (from 17.1% to 24%) was noted between 1956 and 1991, and,
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by 1991, ploughed land represented only 6.3% of the total area. In this latter period,
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forest increased at the expense of grasslands. Taillefumier and Piégay (2003) also
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25 reported that the landscape became simplified after the middle of the 19th century,
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27 changing from a varied mosaic of traditional farming areas to large homogeneous
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29 expanses of forest, shrubs, and grassland. Debussche et al. (1999) compared postcards
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31 showing Hérault (southern France) at the beginning of the 20th century, to the modern
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landscape, and confirmed the disappearance of land devoted to crops and pasture and
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34 the development of forests from the end of the 19th century, caused by rural
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36 depopulation and the almost complete disappearance of livestock. The cited authors also
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38 noted a decline in the area of bench terraces, which were rapidly invaded by shrubs and
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40 trees because the soil was deep and well preserved.
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Several reports have appeared on the extent of land abandonment in Italy, and the
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recolonization of abandoned cultivated fields by forests and shrubs, particularly during
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45 the second half of the 20th century. Abandonment occurred throughout the country,
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47 including the Alps (Renzi et al., 2002; Surian et al., 2010), and in the central (Surian et
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49 al., 2010) and southern regions (Garfi et al., 2007; Duarte et al., 2008).
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51 In Greece, land abandonment has affected many of the terraces constructed on
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steep slopes, both on the mainland and the Aegean Islands (Kizos and Koulouri, 2006;
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Koulouri and Giourga, 2007), and this has led to an expansion of shrubs. For example,
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Koulouri and Giourga (2007) reported that shrubs occupy 64% of early-abandoned plots
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58 on Lesvos Island.
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Farmland abandonment has also been significant in the Swiss and Austrian Alps.
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Gellrich et al. (2007) found that abandonment in the Swiss mountains involved mainly
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former subalpine grasslands; and agricultural land on steep slopes, stony ground, and in
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5 colder regions. Rapid forest regrowth followed. Farmland abandonment in the last few
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7 decades has largely been restricted to areas with a higher proportion of part-time rather
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9 than full-time farmers. This suggests that, in recent times, land abandonment has not
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been affected by migration, in contrast to the pattern seen some decades ago (Gellrich
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and Zimmermann, 2007). Tasser et al. (2007) studied land use changes in the eastern
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Alps, and found that 8-67% of formerly cultivated areas had been abandoned over the
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16 past 150 years; forest regrowth has occurred in most instances. Farmland abandonment
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18 has continued in the years since 1980. In the same area, Tasser and Tappeiner (2002)
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20 noted that abandonment has also affected larch meadows and the less intensively used
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fields of the subalpine and alpine belts.
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Studies on farmland abandonment in eastern European countries have revealed
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25 that the phenomenon is recent. For example, Kozak et al. (2004) noted that one-third of
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27 the cultivated area of the Beskid Maly Mountains (Carpathians, southern Poland) was
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29 abandoned between 1965 and 1997, and the process is continuing. Kuemmerle et al.
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31 (2008) studied the Carpathian Mountains in the triangle bounded by the borders of
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Poland, Slovakia, and the Ukraine, from 1986 to 2000. Since the breakup of the Soviet
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Union in 1989, 13.9% of farmland in the Polish sector has been abandoned, 20.7% in
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36 Slovakia, and 13.3% in the Ukraine.
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40 Abandonment was greater at higher elevations. Reforestation was extensive in
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Slovakia, particularly at higher altitudes (up to 80% at elevations above 700 m). The
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reasons for land abandonment were related to the major economic and political changes
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caused by the transition from centralized to market-oriented economies in eastern
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47 Europe after 1989, resulting in the liberalization of prices and greater competition from
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49 foreign producers. Land abandonment was even more extensive in Latvia; in some
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51 regions 50% of the land under cultivation prior to 1989 had been abandoned by 1999
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(Nikodemus et al., 2005). A similar study of Estonia’s agricultural sector concluded that
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a very rapid process of abandonment occurred between 1990 and 1993, affecting about
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30% of all cultivated land (Peterson and Aunap, 1998). Van Dessel et al. (2008)
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58 compared various land cover maps of the Lake Balaton catchment (Hungary), from
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1981, 2000 and 2005, and concluded that there had been extensive conversion of arable
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agricultural land and vineyards to grassland and forest.
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3

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5 3. Plant colonization in abandoned fields
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7 The process of plant colonization after land abandonment has been widely studied
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9 in various parts of Europe. From a hydromorphological point of view, the
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characteristics of plant colonization (rate and plant composition) affect infiltration rates,
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runoff generation, and soil detachment and sediment transport. It is thus essential to
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understand the various colonization stages and the factors controlling colonization.
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16 Plant colonization in abandoned fields has been defined as a process of secondary
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18 succession (Pugnaire et al., 2006), the complexity of which depends on multiple natural
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20 and human-induced factors including the depth and fertility of the soil; hillslope aspect;
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climate (average annual precipitation, evapotranspiration) (García-Ruiz et al., 1996b;
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Teira and Peco, 2003); the distance from bordering vegetation; the floristic composition
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25 of vegetation at the borders; and external interventions after the land has reverted
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27 (Bunce, 1991).
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29 In general terms, plant colonization involves an increase in vegetation density and
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31 soil protection, as well as a progressive rise in the complexity of plant associations.
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Nevertheless, the abandonment of mountain meadows and colonization of the meadows
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with scrub or trees may represent a decrease in biodiversity (MacDonald et al., 2000)
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36 and homogenization of the landscape (Fig. 2). Various scenarios of land abandonment
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38 are evident (Fig. 3): (i) fields abandoned after 2-3 years of cereal cultivation under
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40 shifting agricultural practices, leaving an impoverished soil with open stubble; (ii)
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sloping or terraced fields (that had typically been cultivated once every 2 years), which
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when abandoned had a relatively dense stubble cover that was commonly grazed by
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sheep; and, (iii) fields which had been meadows producing livestock feed, which were
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47 frequently grazed by cattle after abandonment (Fig. 3). In addition, in the Mediterranean
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49 region, orchards and vineyards may have been established in fields abandoned for
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51 several years.
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Abandoned sloping and terraced fields with stubble typically develop a relatively
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dense herbaceous cover in less than 10 years, at least in humid and sub-humid
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environments, and become grazing meadows. If livestock pressure remains relatively
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58 high, such fields may function as grazing meadows for decades, retarding the transition
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60 to shrubs and trees; in less heavily grazed fields the vegetation will progress quickly
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toward a shrub association (González-Bernáldez, 1991; Tasser et al., 2007;
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Tzanopoulos et al., 2007; Verburg and Overmars, 2009). For this reason, many villages
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in Mediterranean mountain areas are set in a very simple landscape, with grazing
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5 meadows around the village and a more distant surrounding belt of shrubs and forests
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7 that have colonized fields abandoned a long time ago (Vicente-Serrano et al., 2004;
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9 Lasanta et al., 2009). Tzanopoulos et al. (2007) noted that grazing affects vegetation
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succession in various ways. Grazing can delay the transition between vegetation
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communities because grazing inhibits shrub growth, but can facilitate shrub
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colonization of grazing meadows because grazing affects the competing herbaceous
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16 vegetation. Irrespective of the effects seen, the interactions between plant colonization
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18 and grazing seem to be very complex, as emphasized by Chauchard et al. (2007) in a
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20 study in the southern French Alps.
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The rate of shrub colonization depends largely on the availability of shrub species
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in areas surrounding or adjacent to abandoned fields, and it is very common to note a
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25 circumferential pattern of plant colonization until the plot is fully covered by shrubs
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27 (Fig. 4). The persistence of a dense shrub cover will depend on the frequency of fires
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29 and on soil quality (Dunjó et al., 2003). Fire usually takes the plant colonization process
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31 back to the beginning, and this process was very common in Mediterranean
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environments, where fires were deliberately started by shepherds to eliminate thorny
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shrubs and to improve the quality of grasslands (Ruiz-Flaño et al., 1992). Turning to
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36 soil quality, plant colonization occurs quite rapidly on deep soils rich in organic matter.
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38 If a forest is close to an abandoned field with soils of this type, a young forest can
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40 develop in the field in 20 years or less. This has occurred in many continental and
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Atlantic areas of Europe, where fields that were cultivated until abandonment in the
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middle of the 20th century have now become dense forests (Nelson, 1990; Cernusca et
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al., 1996; Debussche et al., 1999; Lach and Wyzga, 2002; Poyatos et al., 2003;
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47 Taillefumier and Piégay, 2003; Andréassian, 2004; Cosandey et al., 2005; Keesstra et
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49 al., 2005; Chauchard et al., 2007; Gellrich et al., 2007; Tasser et al., 2007; Kuemmerle
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51 et al., 2008). In contrast, a dense shrub cover can remain for decades in abandoned
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fields with thin, poorly structured, eroded soils, even if precipitation is sufficient to
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support forest development and forest lies relatively close to the abandoned field
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(Verburg and Overmars, 2009). Under such conditions, the succession of shrubland to
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58 forest may not occur, or is very slow (Pueyo and Beguería, 2007). This has been noted
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60 at some sites in the central southern Pyrenees, where a dense cover of Genista scorpius
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