Agricultural Abandonment in the North Eastern Iberian Peninsula: The ...

Journal of Environmental Planning and Management, Vol. 48, No. 1, 85 – 102, January 2005

Agricultural Abandonment in the North Eastern Iberian Peninsula: The Use of Basic Landscape Metrics to Support Planning ISABEL BIELSA***, XAVIER PONS**{ & BOB BUNCE{ *Centre for Geo-Information, Wageningen, the Netherlands **Department of Geography, Universitat Auto`noma de Barcelona, Bellaterra, Spain { Centre for Ecological Research and Forestry Applications (CREAF), Bellaterra, Spain { Alterra Green World Research, Wageningen, the Netherlands

(Received January 2004; revised July 2004)

ABSTRACT Land abandonment is an important cause of changes in landscape patterns in the Mediterranean area. There is a need to monitor land use and land cover changes in order to provide quantitative evidence of the relationship between land abandonment and the formation of new landscape patterns. Appropriate management policies to encourage sustainable development can then be developed. This paper describes how to monitor landscape dynamics using different temporal land use and land cover data generated from field survey and airborne information. The results showed that the abandonment of agricultural land generally results in an increase of vegetation biomass. This process leads to homogenization of the landscape. In addition, abandonment promotes fragmentation of agricultural land. Based on these results, the paper discusses the implications for rural management policies concerning the abandonment of agricultural land and suggests recommendations for the development of such policies.

Introduction Since the beginning of the 19th century, abandonment of rural land has become a widespread process in many areas within European mountainous regions (LasantaMartı´ nez & Garcı´ a Ruiz, 1996). From the 19th century onwards, the traditional rural system of Mediterranean mountainous areas has been under threat (Naveh, 1991). In part this has been the result of the intrinsic limiting physical factors of the land, combined with regional structural problems. This has been accentuated by the ongoing globalization process which has increased the competition from other agricultural areas with lower production costs (Baldock et al., 1996). As a consequence of these processes, part of the rural population has migrated to urban

Correspondence Address: Isabel Bielsa, Centre for Geo-Information, Wageningen UR, PO Box 47, 6700 AA Wageningen, the Netherlands. Email: [email protected] ISSN 0964-0568 Print/1360-0559 Online/05/010085-18 # 2005 University of Newcastle upon Tyne DOI: 10.1080/0964056042000308166

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and industrialized areas to search for alternative sources of income, causing the progressive abandonment of much rural land (Soriano, 1994; Lasanta-Martı´ nez, 2001; Nadal-Tersa, 2002). The land abandonment discussed here is defined as a gradual decrease of agricultural practices and human inputs (Burel & Baudry, 2001). In particular, the paper will focus on the rural abandonment processes of traditional agricultural systems in the mountainous regions of the Mediterranean in the North Eastern Iberian Peninsula. Land abandonment of marginal land is closely related to a parallel process of intensification in the more accessible areas that have better soils, less steep slopes and have therefore been easier to mechanize (Lasanta-Martı´ nez & Garcı´ a-Ruiz, 1996; MacDonald et al., 2000). The abandonment process has generally involved different patterns of change: (1) (2) (3) (4) (5)

conversion from mixed crops and grazing land to a limited number of monocultural crops; policy aided set-aside; managed re-afforestation; partial abandonment of some parcels, generating a landscape pattern of unused and cropped parcels; total abandonment of agriculture and a progressive transformation of the area into uncultivated land (MacDonald et al., 2000).

The traditional type of agriculture, characteristic of the subsistence economy, was adapted to the limiting factors and obstacles that the natural conditions imposed. These traditional agriculture practices are partly responsible for maintaining high levels of biological diversity. Therefore, semi-natural habitats adjacent to these traditional agricultural practices depend entirely on the continuation of the extensive agricultural practices. Some of them are among the most species-diverse habitats and at the same time characterize the landscape in which they occur (Ostermann, 1998). The polarization of agricultural practices from low-intensity systems into either highly intensified agricultural practices with high external inputs or abandoned agricultural land, threatens biodiversity in many semi-natural areas (Baldock et al., 1996). During the last century these habitats have drastically declined in extent as a result of the polarization of agricultural practices (EEA, 2003). In the mountains of the Mediterranean the traditional landscape pattern is composed of fine-grained fields and small woodlands. Land abandonment has caused intrinsic changes in land management practices and has modified natural landscapes in different ways. As soon as an agricultural field is abandoned, gradual colonization by native species begins. First, annual herbaceous plants germinate but these gradually disappear as perennial herbaceous and low shrubs develop. These in turn supply the conditions for the colonization by woody species (Martı´ nezFernańdez et al., 1994; Nadal-Tersa, 2002). In general, in areas undergoing a land abandonment process there is an increase in the area occupied by semi-natural land cover types, such as shrubs and other taller woody species. The consequences of land abandonment for landscape diversity and landscape patterns are still not fully understood (Farina, 1998). The effect of land abandonment on landscape diversity depends upon the former use of the land. In

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some regions this process may have a beneficial effect on biodiversity, especially if the land abandonment occurs in a uniform and intensive rural landscape such as East Anglia in the UK. In these cases, there will first be an increase of ecological diversity followed by a decrease of diversity (Ruiz-Flanõ & van Hemert, 1994; Farina, 1998; Lasanta-Martı´ nez & Garcı´ a-Ruiz, 1998). However, because of the low resilience of Mediterranean ecosystems, abandonment usually aggravates the negative effects of changes in landscape management. The consequences for landscape dynamics can be summarized as: (1)

(2) (3)

(4) (5)

A reduction or extinction of many species of flora and fauna linked with disappearing cultural diversity (Gonza´lez-Berna´ldez, 1991; Farina, 1997; Sua´rez-Seoane et al., 2002). A change from fine towards coarse-grained patterns of land (Fernańdez-Ales, 1991; Farina, 1998). The reduction or disappearance of open spaces and their transformation into dense scrub which in turn has negative consequences for the aesthetic value of cultural landscapes (Nadal-Tersa, 2002; Serra-Ruiz, 2002). An increase of spatial connectivity of forested patches, resulting in an increased risk of wildfires (Gonza´lez-Berna´ldez, 1991; Lloret et al., 2002). The modification of the geo-morphological processes on slopes which increases the risk of soil erosion. This has a negative effect on soil depth at higher altitudes in mountains and on the quality of abandoned terraces (OrtigosaIzquierdo et al., 1994).

Overall, it is clear that abandonment of land in rural areas of the Mediterranean is generally an unwanted process. Stakeholders and policy makers therefore need essential information on trends in land use to define measures to control the consequences of abandonment. In detail, quantitative information about where, when, why, how and to what degree land is abandoned is required to understand how the landscape structure and pattern are changing and to assess their impact on environmental processes. With this information policy makers would then be better equipped to reduce the loss of landscape diversity and biodiversity following the decline in traditional agriculture. However, it is difficult to provide the necessary information because although technological developments have improved the monitoring and measurement of land use and land cover changes, the information has increased faster than the understanding of the processes (Mather, 1999). The use of GIS (Geographical Information Systems) in landscape studies provides an analytical tool to explore patterns and processes at different landscape scales and facilitates the application of landscape metrics for quantifying landscape pattern changes (Turner et al., 1989; Baker & Cai, 1992; Mcgarigal & Marks, 1995; RegatoPajares et al., 1995; Schumaker, 1996). Landscape metrics are empirical tools that describe the spatial structure of a landscape at a certain scale and time. However, the use of landscape metrics to support landscape planning has so far been limited (Botequilha Leitaõ & Ahern, 2002). This paper proposes a methodological approach for integrating fieldwork data, airborne imagery and landscape metrics in order to study the spatial variation and temporal dynamics of landscape patterns that develop after land abandonment in

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Mediterranean mountainous landscapes. The paper hypothesizes that land abandonment acts as an active agent for the formation of new landscape patterns. To obtain a better understanding of the processes resulting from land abandonment, two hypotheses were formulated: (1) abandonment leads to a decrease of landscape diversity and therefore the landscape becomes more homogeneous; and (2) abandonment increases the fragmentation of rural land. The final objective of this study is to define environmental indicators that provide a basis for rural development plans aiming at preventing ongoing land abandonment and any resulting processes of land degradation. The Study Area The study area selected for this study is located in Catalonia, North Eastern Spain, within the counties of Priorat and Baix Camp (see Figure 1). It covers an area of approximately 900 km2. The main economic activities are agriculture and related industrial activities. The characteristic crops are those traditional to the Mediterranean (i.e. winter cereals, olives, vines, hazelnuts, almonds and carobs) (IEC, 1993a, 1993b). Market demand and EU policies regarding some agricultural crops have influenced the economic development of the area. The prices for olives and wine have increased, whereas the production of almonds and hazelnuts has experienced low market prices. The general socio-economic conditions have caused changes in agricultural management and therefore an increase in land abandonment in the last century. At the end of 19th century the vines were affected by Phylloxera, which led to an economic crisis and many farmers, especially the younger people, had to find jobs elsewhere,

Figure 1. Location map of the study sites in the context of the study area.


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causing large areas of agricultural land to be abandoned. Between 1960 and 1980, the industrial expansion of other parts of the country also resulted in a large-scale exodus of the rural population. At present, about 26% of the population is over 65 years old (IDESCAT, 1996). Traditional farming in this area promoted cultivation of the mountain slopes by constructing stonewalls that formed the terraces to prevent soil erosion and enable cultivation on steep slopes. In general these terraces were narrow with limited accessibility. As a consequence they were difficult to mechanize. These fields were the first ones to be abandoned during periods of economic decline. By contrast, in the last decade, the high demand for Priorat wines has caused an intensification of the best agricultural fields. This has resulted in an increase of the parcel size of land and a transformation into monoculture of vines, especially in the municipalities located within the areas demarcated as denominacio´ d’origen. Livestock farming does not occur in this area of Catalonia. Poultry farming will not be considered in this study as it concerns an industrialized type of farming that is not a land-dependent agricultural activity. Human action has had a strong impact on the landscape of the study area over many centuries with the natural evergreen forest being transformed into a mixed rural and grazing landscape pattern. This formed a stable landscape system (Bolo`s, 1988). However, the decline of agricultural activities in the last century has resulted in the abandonment of marginal fields and caused their gradual colonization by semi-natural vegetation. These fields will develop into scrub (called garrigues locally) combined with Aleppo pine (Pinus halepensis) and eventually into forest (Lo´pezBonillo, 1993). The increased density of combustible vegetation and regular drought periods have stimulated wildfires. Together, these factors have a negative influence on the recovery process of natural and semi-natural vegetation and on the soil forming processes in the abandoned fields. An extended area located within the Priorat and Baix Camp counties has been analysed in this study. From this area a selection of municipalities was made that were characterized by: (1) 80% of the municipal territory above 100 m; and/or (2) continuous depopulation since 1900. A careful selection of four study sites was made on the basis of field visits and the environmental conditions (climate and altitude) of the area. The study sites were characterized by similar socio-economic developments and bio-physical variation that are typical for the whole study region and that, based upon the samples taken from these sites, an assessment of the consequences of land abandonment could be made. Site 1. Located on the coast and covering a total of 62 km2, this is characterized by a mild littoral Mediterranean climate. The landscape within this site can be described as very heterogeneous with altitudes ranging from sea level to 722 m. The most common crops within this area are trees such as hazelnuts, olives and almonds. Some other fruit trees are also grown and there is some horticulture. The farm size varies from 2 to 20 ha. In this area the influence of tourist activities, urban sprawl and transport development has had an important role in land use changes. Site 2. Located within the river valley forming an agricultural landscape pattern and covering 46 km2. Altitudes range from 155 m to 716 m. The climate is more continental, with periods of freezing weather during winter and high temperatures in

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summer. In 1962 the Guiamets reservoir was constructed, making it possible to intensify arable farming through the use of irrigation. The dominant crops are cereals, vines, olives, hazelnuts and almonds. Fruit trees and horticulture can also be found within the area. The farm size varies from 10 to 50 ha. Site 3. Covers 75 km2. This site is situated in a geological depression framed by the mountain ranges of Montsant and Prades with an altitude interval ranging from 340 m to 1164 m. Situated far from the sea (40 to 50 km) and its moderating influence, the climate is continental with cold winters and hot dry summers. The Siurana reservoir, which was constructed in 1974, has been an important factor in enhancing the viability of most of the arable farming activities. The dominant crops are vines, olives, hazelnuts and almonds, fruit trees and horticulture, which are grown on farms with the most common size ranging from 10 to 20 ha. Site 4. This site is located within 741 to 1202 m above sea level and covers 29 km2. The altitude significantly influences the climate. Periods of freezing weather are common and therefore the type of crops that are grown can withstand frost, e.g. winter cereals and hazelnuts. The size of farm in the area ranges from 2 to 20 ha.

Methodology Field Survey The field survey was carried out in April 2000 and aimed to identify abandoned fields with evidence of former agricultural practices. A standard protocol was defined to describe agricultural and abandoned fields (Table 1).

Table 1. Description rules for the recognition of agricultural and abandoned land Land use

Agricultural

. . . . Land use traces . Land cover

. . . . .

Woody crops Shrub crops Herbaceous crops Fallow Evidence of agricultural practices for commercial or subsistence purposes Existing field borders Agricultural terraces are well preserved Absence of invasion of natural vegetation Shrub and woody crops are managed Irrigation may exist

Abandoned . . . . .

Forest land Shrub land Bare soil Rocky areas No evidence of agricultural practices (i.e. ploughing, tillage, irrigation, pruning) . Field borders are unclear . Agricultural terraces are still recognizable but not maintained . Crop species may remain . Succession and colonization by natural species . Presence of environmental disturbance: fire, erosion, open earth extraction


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Information about the vegetation composition and the presence of former agricultural crops was gathered within the abandoned fields as well as the vegetation structure and coverage. Based upon this information the time of abandonment was estimated. The information collected in the field survey provided detailed information about the present land utilization that complements the information provided by aerial photograph interpretation. Generation of Temporal Land Cover and Land-use Maps To detect land abandonment, to quantify land cover changes and to characterize landscape patterns, two land cover maps (corresponding to years 1956 and 1993) were obtained and analysed. The 1956 land cover and land-use map was derived from photo interpretations of the aerial photographs (1956, flight scale: 1:30 0000) which were scanned and orthorectified using a digital elevation model. The scale of the resulting orthophotos can be considered to be about 1:25 000, with a pixel size of 2 m. Arable land in 1956 was identified using photo interpretation. Polygons of arable land were digitized on screen. The resulting vector map is composed of two classes: arable and non-arable land. The land cover and land-use map of 1993 was derived from the existing land cover map of Catalonia at the scale of 1:25 000 (CREAF, 2002). For the final analysis, the resulting polygons of arable land in 1956 and 1993 were then converted into a grid of 2 m. A patch is used as the unit to analyse the landscape change in this study. The patch is the smallest mapped area of land with specific homogeneous land cover characteristics (Forman, 1995). In a raster GIS, the landscape pattern is interpreted synoptically by a configuration of patches, which are represented geometrically by a contiguous cluster of homogeneous pixels with the same land cover. A patch grid is created for each year by a clumping method which groups neighbouring cells based on the same land cover thematic information (Macgarigal & Marks, 1995; Elkie et al., 1999). To minimize the effect of possible positional errors incurred when interpreting and digitizing maps and to prevent slivers, two procedures were adopted: (1) a buffer of 10 m in each direction was calculated from the transport networks such as roads and railways existing in both years. The resulting polygons were subtracted from the land use maps; (2) polygons smaller than 500 m2 were considered as slivers and were excluded from the analysis. Quantifying Landscape Dynamics and Pattern In order to identify and to determine the spatial distribution of abandoned patches, the land cover maps of 1956 and 1993 were overlaid. The patches that were classified as arable in 1956 and non-arable in 1993 were assumed to be abandoned or to have changed into another type of land cover. In order to investigate whether land abandonment is causing a reduction of landscape diversity, changes in land cover and land use of arable land were analysed. Landscape diversity describes the equality of the proportion of land cover types in the landscape (Frohn, 1998). A reduction in the number of land cover types present in time indicates that there is a process of homogenization of the landscape.

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Table 2. Overview of landscape change indicators used in the analysis Number of patches Mean patch size Mean shape index Area Weighted Mean Shape Index

NUMP MPS MSI AWMSI

Total number of patches Average patch size Measure of shape complexity Measure of shape complexity

Using landscape metrics, the relationship between the process of land abandonment and landscape pattern formation was explored using four types of indicators (Table 2). The size, edge and shape characteristics of arable patches in 1956 – 1993 and the resulting abandoned patches were analysed with Spatial Analyst (Mcgarigal & Marks, 1995; Elkie et al., 1999). Fragmentation is a process by which elements in the landscape are getting smaller and isolated (Forman, 1995; Gulinck & Wagendorp, 2002). The number of patches (NUMP) and the mean patch size (MPS) were used to describe patch number and area characteristics, and are indicators of a reduction of landscape grain, an intrinsic process that is characteristic of landscape fragmentation. To describe the shape of patches, the mean shape index (MSI) and the area weighted mean shape index (AWMS) were used. MSI measures the average perimeter-to-area ratio for a particular patch type, while AWMSI weights patches according to their size. If shape metrics decrease in time they refer to a landscape change process of homogenization.

Results Changes in Vegetation on the Basis of Field Survey Data The process of land abandonment has caused significant landscape changes within the area. In general, the consequence of land abandonment has been the increase of vegetation biomass. Land use has determined the type of land cover and the degree of land cover change is the direct result of the abandonment of agricultural land-use practices. Land abandonment, considered as a type of land use, implies a gradual transition from arable land to a semi-natural land cover type, according to the colonization stage of the natural vegetation. Wildfires can delay this succession process and the recovery of vegetation. As a consequence, frequently the resulting semi-natural land cover types do not have a direct relationship with the time elapsed since the abandonment of the land. During the first stage of abandonment (less than five years), the land is invaded by low, predominantly annual, herbaceous species while remains of the original crops are still present. In all cases hazelnut trees with abundant field grasses and tall herbs occupy these fields. The estimation of whether a field is abandoned based only on the herbaceous species coverage could be subject to misinterpretation, especially in cases when farmers did not fully abandon their agricultural plots but only decreased the management intensity. Indeed, interviews with farmers gave the additional information needed for making a correct assessment. In the second stage of abandonment (between 5 and 30 years) lower shrubs and scrubs are dominant, with the most abundant species being Erica multiflora, Rosmarinus officinalis and Ulex parviflorus. Scattered specimens of young


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Pinus halepensis have also already invaded some fields. In the third stage of abandonment (more than 30 years) tree crowns and woody species are present within the abandoned plots. The most common trees are Pinus halepensis and Pinus sylvestris with thick undergrowth of tall shrubs and scrubs (e.g. Juniperus oxycedrus, Rosmarinus officinalis, Ulex parviflorus). The most common remaining tree crops are hazelnuts, olives and carobs (Corylus avellana, Olea europea and Ceratonia siliqua). The final stage where former agricultural fields are completely covered by forest is rare in the study area, since wildfires have usually played an important role in delaying the final stage of the natural succession. Dynamics of Land Use and Land Cover and Analysis of the Landscape Pattern Change Site 1. In this site land abandonment has caused important landscape changes. In 1956 arable land occupied 32.7% of the site, while in 1993 this was reduced to 14.8%, which in absolute numbers means a reduction in arable land of 1 114.6 ha. Hence the majority (53%) of the arable land in existence in 1956 could be classified as being completely abandoned (Table 3). Only a very small part obtained a new function: e.g. a very small share was converted into built-up areas (1.9%), transport infrastructure (1.7%), open quarries (0.2%) and recreational areas (0.1%) (Table 4 and Figure 2). The analysis of the land cover change also showed that the land abandonment process had produced an increase in scrubs and forested areas. In the period under

Table 3. Evolution of the arable land since 1956 1956 Site 1 2 3 4

1993

Total area Arable land % of Arable land % of (ha) (ha) total area (ha) total area 6205.05 4675.46 7589.94 2950.75

2029.76 2737.83 3453.93 798.52

32.71 58.56 45.51 27.07

915.21 2384.84 2658.92 542.77

Abandoned % of 1956 land (ha) arable land

14.75 51.01 35.04 18.40

1097.17 358.89 823.89 233.36

53.44 12.96 23.54 29.27

Table 4. Change in the share of arable land (1956 – 1993) and shift into other land use types Site Land use type Abandoned Built-up areas Transport network Recreational areas Water bodies Open quarries

1

2

3

4

53.44 1.91 1.73 0.13 0.00 0.18

12.96 0.79 0.05 0.00 0.03 0.07

23.54 0.29 0.00 0.03 0.49 0.00

29.27 2.01 0.00 0.59 0.06 0.00

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Figure 2. Change in the share of agricultural land between 1956 and 1993. Values of less abundant land use classes showed in Table 4 (built up areas, transport network, recreational areas, water bodies, open quarries) are grouped into the ‘others’ category.

analysis, 74.4% of the abandoned agricultural land had developed into scrubs and 13.8% into dense forest. However, the conversion of abandoned land into other land cover types is less significant (i.e. open forest 3.2%, herbaceous 2.9%, bare soil 2.8%, rocky area 2.5% and re-afforestation 0.2%) (Table 5 and Figure 3). The landscape structure had changed from a coarse grain landscape type to a fine grain (Table 6). Present results show that not only has the area of arable land reduced but also the number of patches (NUMP) (from 169 to 151) and the average patch size (MPS) (from 12 ha to 6.1 ha). The arable patch shape was more complex in 1956 than in 1993, since the mean shape index (MSI) in 1993 is 2.0 while the average mean shape index (AWMSI) is 4.2. Therefore the arable patch was reduced in size and the shape became less complex. With regard to abandoned land, it is characterized as having a large number of patches with a very small average size (MPS) (2.5 ha) compared to the average patch size (MPS) of arable patches (6.1 ha). The complexity of the shape of abandoned patches is not a function of the size since average patch shape (MSI) is 2.2 while the area-weighted MSI (AWMSI) is 3.7. This implies that in Site 1 between 1956 and 1993 abandonment of rural land has caused a significant fragmentation of arable land and abandoned land. Abandoned land has been converted mainly to scrubs, which indicates an increase of landscape homogenization. Aridity of this site is higher than the other sites and it may limit forest development. Site 2. Site 2 is characterized by having the highest share of arable land of all sites studied. The arable land has reduced from 58.6% to 51% of the total area, which in absolute numbers only represents a reduction of 353 ha. That is, 13% of the arable land of 1956 has been abandoned (Table 3). The transition of arable land into other land-use types is relatively insignificant, with only 0.8% of the arable land of 1956 converted into built-up areas, less than 1% into either open quarries, transport infrastructure or water bodies (Table 4 and Figure 2). The recovery of vegetation of


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Table 5. Proportional transition of the land cover in abandoned land Site Land cover type

1

2

3

4

Scrubs Dense forest Open forest Herbaceous Riparian forest Re-afforestation Rocky area Bare soil

74.41 13.77 3.21 2.93 0.00 0.22 2.52 2.88

43.67 42.28 7.48 5.09 0.92 0.00 0.3 0.3

65.88 25.19 2.63 2.12 0.78 0.00 2.76 0.59

38.29 55.89 2.83 1.46 0.78 0.00 0.03 0.64

Figure 3. Land cover transition in percentages of the abandoned land (1993). Values of less abundant land cover classes showed in Table 5 (riparian forest, re-afforestation, rocky area, bare soil) are grouped into the ‘others’ category.

abandoned areas shows the same tendency as in Site 1, with an increase of scrubs and dense forest of 43.7% and 42.3%, respectively. Less significant was the conversion of abandoned agricultural land into open forest (7.5%) and herbaceous species coverage (5.1%) (Table 5 and Figure 3). The landscape pattern of arable land in 1956 is characterized by a coarse patch size, typical of well-consolidated agricultural land occupying the flat river terraces in this site (Table 6). The evolution of the arable patches until 1993 shows an increase of 30 in the number of patches (NUMP) and a decrease of average patch size (MPS), although the high value in SD (standard deviation) in 1956 and 1993 indicates a high variability of arable patch size. Results obtained from the shape metrics analysis indicate that the evolution of the arable patch shape between 1956 and 1993 remains stable since the area-weighted mean shape index (AWMSI) remains 4.0.

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Table 6. Agricultural and abandoned patches: dynamics of landscape pattern Size metrics Total area ha Site 1 Agriculture 1956 Agriculture 1993 Abandoned 1993 Site 2 Agriculture 1956 Agriculture 1993 Abandoned 1993 Site 3 Agriculture 1956 Agriculture 1993 Abandoned 1993 Site 4 Agriculture 1956 Agriculture 1993 Abandoned 1993

6205.05 2029.76 915.21 1097.17 4675.46 2737.83 2384.84 358.89 7589.94 3453.93 2658.92 823.89 2950.75 798.52 542.77 233.36

Shape metrics

NUMP

MPS (SD) ha

MSI

AWMSI

169 151 437

12.01 (50.30) 6.06 (15.34) 2.51 (7.50)

2.10 2.03 2.15

6.67 4.17 3.68

83 113 202

32.98 (93.26) 21.10 (75.48) 1.78 (4.02)

2.16 2.10 2.03

4.04 4.04 3.10

251 336 587

13.76 (92.57) 7.91 (34.98) 1.40 (2.60)

2.12 2.11 2.05

9.71 6.57 2.79

107 83 177

7.46 (58.09) 6.53 (23.11) 1.30 (2.30)

1.92 1.91 1.87

7.66 3.04 2.27

Note: NUMP: Number of patches; MPS: Mean patch size; SD: Standard Deviation; MSI: Mean Shape Index; AWMSI: Area Weighted Mean Shape Index.

The abandoned land is characterized by a considerable number of small patches, as the number of patches (NUMP) is 202 and the average patch size (MPS) is 1.8 ha. The shape of abandoned patches is less complex than the remaining arable land (Table 6). The abandonment of rural land has been less significant in Site 2 between 1956 and 1993 than in Site 1. However, landscape structure is also characterized by a general fragmentation process of the arable land by a general reduction of patch size and an increase in the number of arable patches. The abandoned land that results is also fragmented, with very scattered small patches adjacent to agricultural fields. Site 3. The area covered by arable land has reduced between 1956 – 1993 from 45.5% to 35.0% of the total area in this site. This is an absolute decrease of 7951 ha of arable land, which means that 23.5 % of the arable land of 1956 could be classified as being abandoned in 1993 (Table 3). The remainder of the arable land has been transformed into water bodies (0.5%), built-up areas (0.3%) and recreational areas (0.05%) (Table 4 and Figure 2). Abandoned land has been predominantly transformed into scrubs (65.9%) and dense forest (25.2%) followed by rocky area (2.8%), herbaceous vegetation (2.1%), riparian forest (0.8%) and bare soil (0.6%) (Table 5 and Figure 3). Results obtained by landscape metrics indicate considerable changes in the landscape pattern between 1956 – 1993 (Table 6). The evolution of the number of arable patches (NUMP) shows a large increase from 251 patches in 1956 to 336 patches in 1993. This, combined with a significant decrease of the average patch size (MPS) from 13.8 ha to 7.9 ha, reveals the common trend of fragmentation of the rural landscape. The higher standard deviation of the average patch size (MPS) in


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1956 may indicate that arable patches were more heterogeneous in size than in 1993. Bigger arable patches become more complex in shape, as the average shape index (MSI) of 1956 and 1993 is 2.1 in both areas, while the area-weighted MSI (AWMSI) is 9.7 in 1956 and 6.6 in 1993. With regard to abandoned land, it is characterized by a large number of patches (NUMP) 587 with very small average size (MPS) (1.4 ha). The shape of the abandoned patches is less complex than that of the remaining arable patches. The overall results indicate that in this site there is a general landscape homogenization and fragmentation process of agricultural and abandoned land. The abandoned fields have been colonized mostly by scrubs. Site 4. From 1956 to 1993, arable land has decreased from 27.1% to only 18.4% of the total area of the study site (Table 3). In total there has been a decrease of 255.8 ha. of arable land, of which 29.3% has been abandoned and 2% has been converted into built-up areas. The remainder of the land cover changes are very small, e.g. 0.6% to recreational areas and 0.1% to water bodies (Table 4 and Figure 2). Abandoned land has contributed to the increase of semi-natural land cover types as 38.3% was transformed into scrubs, 55.9% into dense forest and 2.8% into open forest. Less significant are the conversions into herbaceous species (1.5%), riparian forest (0.8%) and bare soil (0.6%) (Table 5 and Figure 3). The evolution of the number of arable patches (NUMP) shows a general decrease of arable patches from 107 to 83 (Table 6). The average patch size (MPS) in 1993 showed that the arable patches in 1956 changed into smaller patches. The higher standard deviation of the average patch size (MPS) of the arable patches in 1956 indicates a trend towards a larger heterogeneity in the size of arable patches than in 1993. Bigger arable patches have become more complex in shape, as the average shape index (MSI) of 1956 and 1993 was 1.9 for both years, while the area-weighted MSI (AWMSI) was 7.7 in 1956 and only 3 in 1993. Abandoned land in 1993 is characterized by a considerable number of very small patches (1.3 ha). The shape of abandoned patches is less complex than that of the arable patches. Overall, this indicates that in this site fragmentation is seen as the main trend of agricultural and abandoned land. Abandoned land has been colonized by dense forest that may have been supported by favourable abiotic conditions of this site (i.e. soils and climatic conditions). Discussion The study shows a significant decrease in area occupied by agricultural land, most of which was converted into abandoned land. Land abandonment has resulted in an increase of semi-natural vegetation composed of either scrub or open forest. The abandonment of arable land is linked to a general fragmentation process. Research in other parts of Spain and the Mediterranean show similar results (e.g. FernańdezAles, 1991; Farina, 1998). In the area under investigation the fragmentation is characterized by a general reduction of patch size and either an increase (Sites 2 and 3) or a decrease (Sites 1 and 4) in the number of arable patches. The abandoned land that results is fragmented, with scattered small patches. The spatial distribution of abandoned land shows different trends: (1) abandoned areas next to agricultural

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areas; (2) scattered parcels adjacent to agricultural fields; and (3) large abandoned areas situated far away from agricultural and built-up areas. These results indicate important changes in landscape structure, which have implications for the biodiversity found in the habitats adjacent to the arable systems. The fact that the process of land abandonment leads to an overall increase of vegetation biomass is controversial, since it could be normally assumed to have beneficial effects on landscape diversity. However, the homogenization of the agricultural land pattern, caused by the abandonment of traditional agricultural systems, has negative effects in terms of available food and habitat for some rare and threatened species of diverse flora and fauna associated with these traditional activities (Gonza´lez-Berna´ldez, 1991; Farina, 1997; Suarez-Seoane et al., 2002). It was found that the gradual regeneration of semi-natural vegetation in abandoned fields is very slow, i.e. 30 years are needed for complete coverage of semi-natural vegetation. Similar results have been reported in other parts of Spain (Romero-Calcerrada & Perry, 2004). The general successional trend in the region is from abandoned land first into open scrub, then dense scrub and finally to the forest climax formation of the region, Holm-oak forest (Quercus ilex) (Bolo`s, 1988). However, the climax stage of the succession process was not found within the abandoned fields. In the study sites the general trend of abandoned land has been the conversion into garrigue open scrub and then the final stage open forest with a dominance of Aleppo pine (Pinus halepensis) with a thick undergrowth of tall scrubs. This indicates a general process of landscape homogenization. Similar results have been reported in other parts of Catalonia (Lloret et al., 2002; SerraRuiz, 2002). In the study area wildfires have played an important role in delaying the natural succession process. As shown by other studies (Lloret et al., 2002; Romero-Calcerrada & Perry, 2004) land abandonment in the Mediterranean region creates homogeneous landscapes that are prone to larger and more intense fire. A relevant relationship has been found between the risk of wildfires and the increase of Pinus halepensis, due to its highly flammable nature (Terradas et al., 1998; Trabaud, 2000). Vegetation colonization plays an important role in soil conservation of abandoned fields. There is particular interest in Spain in the relationship between land abandonment and geo-morphological processes due to the vulnerability of abandoned fields to soil erosion caused by the typical Mediterranean rainstorms occurring in spring and autumn (Gallart & Llorens, 1994; Ortigosa-Izquierdo et al.,1994; Cerda`, 1995; Imeson et al.,1998). Therefore, the time lapse from when the field is abandoned to when it is colonized by vegetation is crucial to prevent soil erosion and landscape degradation. For example, vegetation colonization increases water infiltration, thereby reducing water runoff and decreasing evapo-transpiration of the soil and sediment runoff (Gallart & Llorens, 1994; Marco-Molina & PadillaBlanco, 1995; Lasanta-Martı´ nez, 2001). Similar problems of agricultural abandonment are not only taking place on a large scale in Catalonia but have also been reported in many other European mountainous regions (MacDonald et al., 2000). In Mediterranean rural areas abandonment usually goes hand-in-hand with unwanted negative effects on soil quality (through erosion and wildfires), landscape quality and diversity and related biodiversity. Therefore, European and local policies need to address this on-going process. An


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effective European agricultural policy aimed at encouraging landscape diversity should be put in place, with targeted measures to manage abandoned land aimed at preventing the loss of diversity of species and aesthetic values of the landscape. Possible measures could be to give incentives and to promote land stewardship at a regional level. The land stewardship is a partnership between the civil population, landowners and regional government aimed at the protection of natural and cultural values of the landscape, including the traditional activities of the area (ArquimbauCano et al., 2001). In 2000 land stewardship was founded for the first time in Catalonia. The implications of this initiative are to foresee problems in the future in the mid-term. Possible measures at a local level, to stop or compensate for the adverse problems related to abandonment, should be targeted at managing the succession processes of vegetation. This can be realized by encouraging the development of those ecosystems that have greater conservation values by stimulating more diversity in terms of species composition (i.e. selecting and planting native species to accelerate the secondary succession into garrigue scrub lands) in order to provide the basis for a quick transition to the forest climax formations of the region, Holm-oak forest (Quercus ilex). These measures could help to diminish the risk of soil erosion and wildfire propagation. Conclusion This study has developed a stepwise methodology to monitor land abandonment and its effects on landscape structure. Simple metrics such as area and shape metrics were used to obtain a better understanding of the process of abandonment in relation to changes in landscape structure, such as landscape fragmentation and homogenization. The study showed that this abandonment process in agricultural land in mountainous areas of the Mediterranean, where farming is usually of a traditional nature, has a major impact on the structure of the landscape, which is mostly not beneficial for landscape diversity. Abandonment is a complex process that takes place over a long period of time. Preventing land abandonment is difficult due to the broad interaction of causal factors that are involved in this process, which have not only ecological but also socio-economic components. Whether policy measures are taken to prevent the disappearance of the often low-productive traditional agriculture practices is a matter of choice and priority setting of policy makers. It is thought that at present there is a general awareness of the importance of traditional agricultural farming for preserving landscape diversity and character. Therefore, it is possible to be optimistic that future partnerships among landowners, stakeholders and planners will help to promote landscape conservation for future generations. Acknowledgements This research was supported by the Schuurman-Schimmel van Outeren Stichting as part of a PhD research grant to Isabel Bielsa. The first author is grateful to the Department of Geography of the Universitat Auto`noma de Barcelona for access to

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information and research logistics. The authors wish to thank Dr Rob Jongman, Dr Ron van Lammeren of Wageningen University and Professor Dr Steven de Jong of Utrecht University for their support in this research. Dr Berien Elbersen is also thanked for useful comments that helped to clarify the manuscript. References Arquimbau-Cano, R., Pietx-Colom, J. & Rafa-Fornieles, M. (2001) La Custo`dia del Territori. Una Guia per a la Implantacio´ a Catalunya (Manlleu: Fundacio´ Territori i Paisatge, Caixa Catalunya). Baker, W. L. & Cai, Y. (1992) The r.le programs for multi-scale analysis of landscape structure using the GRASS Geographical Information System, Landscape Ecology, 7(4), pp. 291 – 302. Baldock, D., Beaufoy, G., Brouwer, F. & Godeschalk, F. (1996) Farming at the Margins. Abandonment or Redeployment of Agricultural Land in Europe (London & The Hague: IEEP, LEI-DLO). Bolo`s de, O. (1988) La vegetacio´, in: R. Folch-Guille`n (Ed.) Natura, u´s o Abu´s? Llibre Blanc de la Gestio´ de la Natura als Paı¨sos Catalans (Barcelona: Editorial Barcino). Botequilha Leitaõ, A. & Ahern, J. (2002) Applying landscape ecological concepts and metrics in sustainable landscape planning, Landscape and Urban Planning, 59, pp. 65 – 93. Burel, F. & Baudry, J. (2001) Ecologıá del Paisaje. Conceptos, Me´todos y Aplicaciones (Madrid: Ediciones Mundi-Prensa). Cerda`, A. (1995) Impacto del abandono del cultivo sobre la pe´rdida de suelo y agua en un ambiente semia´rido. Cuenca del rı´ o Guadalentı´ n, Murcia, in: XIV Congreso Nacional de Geografıá. Cambios Regionales a Finales del Siglo XX, Salamanca, 5 – 8 diciembre (Salamanca: Asociacioń de Geo´grafos Espanõles, Universidad de Salamanca, Departamento de Geografı´ a). CREAF (2002) Land Cover Map of Catalonia (Catalonia: Centre for Ecological Research and Forestry). Available at http://www.creaf.uab.es/mcsc/descriptiu.htm (accessed 7 April 2002). EEA (2003) Europe’s Environment: The Third Assessment (Copenhagen: European Environment Agency). Available at http://reports.eea.eu.int/environmental_assessment_report_2003_10/en (accessed 1 June 2003). Elkie, P., Rempel, R. & Carr, A. (1999) Patch Analyst User’s Manual (Ontario: Nature Resources Northwest Science & Technology, Thunder Bay). Farina, A. (1997) Landscape structure and breeding bird distribution in a sub-Mediterranean agroecosystem, Landscape Ecology, 12, pp. 365 – 378. Farina, A. (1998) Principles and Methods in Landscape Ecology (Cambridge: Chapman & Hall). Fernańdez-Ales, R. (1991) Effect of economic development on landscape structure and function in the Province of Seville (SW Spain) and its consequences on conservation, in: J. Baudry & B. Bunce (Eds) Land Abandonment and its Role in Conservation, Proceedings of the Zaragoza (Spain) Seminar (Zaragoza: Options Me´diterraneés). Forman, R. T. T. (1995) The Ecology of Landscapes and Regions (Cambridge: Cambridge University Press). Frohn, R. C. (1998) Remote Sensing for Landscape Ecology: New Metric Indicators for Monitoring, Modeling, and Assessment of Ecosystems (Boca Raton: Lewis Publishers). Gallart, F. & Llorens, P. (1994) Papel de los cultivos de montanã y su abandono en la economı´ a del agua, in: J. M. Garcı´ a-Ruiz & T. Lasanta-Martı´ nez (Eds) Efectos Geomorfolo´gicos del Abandono de Tierras, Zaragoza, 12 – 13 de septiembre (Zaragoza: Sociedad Espanõla de Geomorfologı´ a, Instituto Pirenaico de Ecologı´ a (CSIC) Institucioń Fernando Cato´lico). Gonza´lez-Berna´ldez, F. (1991) Ecological consequences of the abandonment of traditional land use systems in central Spain, in: J. Baudry & R. Bunce (Eds) Land Abandonment and its Role in Conservation, Proceedings of the Zaragoza (Spain) Seminar (Zaragoza: Options Me´diterraneés). Gulinck, H. & Wagendorp, T. (2002) References for fragmentation analysis of the rural matrix in cultural landscapes, Landscape and Urban Planning, 58, pp. 137 – 146. IEC (1993a) Cens Agrari 1989. Baix Camp. Monografies Comarcals (Barcelona: Institut d’Estadı´ stica de Catalunya, Generalitat de Catalunya). IEC (1993b) Cens agrari 1989. Priorat. Monografies Comarcals (Barcelona: Institut d’Estadı´ stica de Catalunya. Generalitat de Catalunya).


101

IDESCAT (1996) Institut d’estadı´ stica de Catalunya, Generalitat de Catalunya. Available at http:/ www.idescat.es (accessed 1 June 2004). Imeson, A. C., Cammeraat, L. H. & Prinsen, H. (1998) A conceptual approach for evaluating the storage and release of contaminants derived from process based land degradation studies: an example from the Guadalentı´ n basin, Southeast Spain, Agriculture, Ecosystems and Environment, 67, pp. 223 – 237. Lasanta-Martı´ nez, T. (2001) Despoblacioń y Marginacioń en la Sierra Riojana (Logronõ: Gobierno de La Rioja). Lasanta-Martı´ nez, T. & Garcı´ a Ruiz, J. M. (Eds) (1996) Erosioń y Recuperacioń de Tierras en A´reas Marginales: Casos Praćticos Aplicables a La Rioja (Logronõ: Instituto de Estudios Riojanos, Sociedad Espanõla de Geomorfologı´ a). Lasanta-Martı´ nez, T. & Garcı´ a-Ruiz, J. M. (1998) La gestioń de los usos del suelo como estrategia para mejorar la produccioń y la calidad del agua. Resultados experimentales en el Pirineo Central espanõl, Cuadernos de Investigacioń Geogra´fica, XXIV, pp. 39–57. Lloret, F., Calvo, E., Pons X. & Dı´ az-Delgado, R. (2002) Wildfires and landscape patterns in the Eastern Iberian Peninsula, Landscape Ecology, 17, pp. 745 – 759. Lo´pez-Bonillo, D. (1993) Priorat, in: Consell, Comarcal, Baix, Penede`s and Diputacio´ de Tarragona (Eds) Geografia de les Comarques de Tarragona (Tarragona: Diputacio´ de Tarragona). MacDonald, D., Crabtree, J. R., Wiesinger, G., Dax, T., Stamou, N., Fleury, P., Gutie´rrez-Lazpita, J. & Gibon, A. (2000) Agricultural abandonment in mountain areas of Europe: environmental consequences and policy response, Journal of Environmental Management, 59, pp. 47 – 69. Marco-Molina, J. A. & Padilla-Blanco, A. (1995) Colonizacioń vegetal en terrazas de cultivo abandonadas del sureste peninsular, in: XIV Congreso Nacional de Geografıá, Cambios Regionales a Finales del Siglo XX, Salamanca, 5 – 8 diciembre (Salamanca: Asociacioń de Geo´grafos Espanõles, Universidad de Salamanca, Departamento de Geografı´ a). Martı´ nez-Fernańdez, J., Martı´ nez-Fernańdez, J. & Lo´pez-Bermu´dez, F. (1994) Evolucioń de algunas propiedades eda´ficas y de la vegetacioń en campos abandonados en ambiente semia´rido Mediterrańeo, in: J. M. Garcı´ a-Ruiz & T. Lasanta-Martı´ nez (Eds) Efectos Geomorfolo´gicos del Abandono de Tierras, Zaragoza, 12 – 13 de septiembre (Zaragoza: Sociedad Espanõla de Geomorfologı´ a. Instituto Pirenaico de Ecologı´ a (CSIC), Institucioń Fernando el Cato´lico). Mather, A. S. (1999) Editorial: land use and land cover change, Land Use Policy, 16, p. 143. Mcgarigal, K. & Marks, B. J. (1995) FRAGSTATS: Spatial Pattern Analysis. Program for Quantifying Landscape Structure (Portland, OR: US Department of Agriculture, Forest Service). Nadal-Tersa, J. (2002) Evolucio´ del paisatge de la muntanya mitjana mediterra`nia. Variacions en la fertilitat del so`l i en l’exportacio´ de nutrients al massı´ s de Sant Llorenç del Munt i la Serra de l’Obac (Serralada Prelitoral Catalana) PhD Thesis, Universitat Auto`noma de Barcelona, Bellaterra. Naveh, Z. (1991) Mediterranean uplands as anthropogenic perturbation-dependent systems and their dynamic conservation management, in: O. Ravera (Ed.) Terrestrial and Aquatic Ecosystems: Perturbation and Recovery (New York: Ellis Horwood). Ortigosa-Izquierdo, L., Oserı´ n-Elorza, M. & Arnaéz-Vadillo, J. (1994) Comportamiento geomorfolo´gico del espacio agrario abancalado en Cameros Viejo (Sistema Ibe´rico): resultados de una modelizacioń territorial, in: J. M. Garcı´ a-Ruiz & T. Lasanta-Martı´ nez (Eds) Efectos Geomorfolo´gicos del Abandono de Tierras, Zaragoza, 12 – 13 de septiembre (Zaragoza: Sociedad Espanõla de Geomorfologı´ a, Instituto Pirenaico de Ecologı´ a, (CSIC), Institucioń Fernando el Cato´lico). Ostermann, O. P. (1998) The need for management of nature conservation sites designated under Natura 2000, Journal of Applied Ecology, 35, pp. 968 – 973. Regato-Pajares, P., Castejoń, M., Tella, G., Gimeńez-Caballero, S., Barrera I. & Elena-Rosello´, R. (1995) Analysis of landscape changes in Mediterranean mountain regions of Spain: seven case studies, in: R. H. G. Jongman (Ed.) Ecological and Landscape Consequences of Land Use Change in Europe. Proceedings of the first ECNC seminar on land use change and its ecological consequences, Tilburg, 16 – 18 February (The Netherlands, ECNC). Romero-Calcerrada, R. & Perry, G. L. W. (2004) The role of land abandonment in landscape dynamics in the SPA (Encinares del rı´ o y Cofio, Central Spain, 1984 – 1999), Landscape and Urban Planning, 66(4), pp. 217 – 232.

102

I. Bielsa et al.

Ruiz-Flanõ, P. & van Hemert, H. (1994) Una aproximacioń al balance de sedimentos de cuencas con cultivos abandonados: el ejemplo del Flysch pirenaico, in: J. M. Garcı´ a-Ruı´ z & T. Lasanta-Martı´ nez (Eds) Efectos Geomorfolo´gicos del Abandono de Tierras, Zaragoza, 12 – 13 de septiembre (Zaragoza: Sociedad Espanõla de Geomorfologı´ a, Instituto Pirenaico de Ecologı´ a, (CSIC), Institucioń Fernando el Cato´lico). Schumaker, N. H. (1996) Using landscape indices to predict habitat connectivity, Ecology, 77(4), pp. 1210 – 1225. Serra-Ruiz, P. (2002) Dina`miques del paisatge agrari a l’alt Amporda` (1977 – 1997). Un ana`lisi a partir de la teledeteccio´ i dels Sistemes de informacio´ geogra`fica. PhD Thesis, Universitat Auto`noma de Barcelona, Bellaterra. Soriano, J. M. (1994) Efectes del despoblament sobre el medi fı´ sic d’un territori de muntanya (Tuixent, Parc Natural Cadı´ ’Moixero´). Estudi de la variacio´ de la fertilitat del so`l en camps de conreu abandonats. PhD Thesis, Universitat Auto`noma de Barcelona, Bellaterra. Sua´rez-Seoane, S., Osborne, P. E. & Baudry, J. (2002) Responses of birds of different biogeographic origins and habitat requirements to agricultural land abandonment in Northern Spain, Biological Conservation, 105, pp. 333 – 344. Terradas, J., Pinõl, J. & Lloret, F. (1998) Risk factors in wildfires along the Mediterranean coast of the Iberian Peninsula, in: L. Trabaud (Ed.) Fire Management and Landscape Ecology (Washington, DC: International Association of Wildland Fire, Fairfield). Trabaud, L. (2000) Post-fire regeneration of Pinus halepensis forests in the West Mediterranean, in: G. Ne’eman & L. Trabaud (Eds) Ecology, Biogeography and Management of Pinus halepensis and Pinus brutia. Forest Ecosystems in the Mediterranean Basin (Leiden, the Netherlands: Backhuys). Turner, M. G., O’Neil, R. V., Gardner, R. H. & Milne, B. T. (1989) Effects of changing spatial scale on the analysis of landscape pattern, Landscape Ecology, 3(4), pp. 153 – 162.