Short communication
Impact assessment of changes in land use/conservation
practices on soil erosion in the PenedeÁs±Anoia
vineyard region (NE Spain)
Jose A. MartõÂnez-Casasnovas
*, IneÂs SaÂnchez-Bosch
Department of Environment and Soil Science, University of Lleida, Rovira Roure 177, E25198 Lleida, Spain
Received 20 January 2000; received in revised form 20 June 2000; accepted 28 June 2000
Abstract
Soil erosion by water is one of the most important land degradation processes in the Mediterranean basin. In comparison with other typical crops in this region, vineyards are the agricultural land use that cause the highest soil losses. The changes in land use types and management that have involved the intensi®cation of agriculture from the 1950s have contributed to the increase of soil erosion. This paper presents an assessment of this impact in a vineyard region of fundamental concern in the NE Spain, the PenedeÁs±Anoia, mainly dedicated to the production of high quality wines and ``cavas''. The analysis is based on the comparison of the estimated soil loss rates in the period just before the mechanisation (1950s) and in the most recent past (1990s). Multitemporal data (aerial photographs and digital terrain models), the revised universal soil loss equation and GIS analysis were used for that purpose. The results show a clear negative soil loss balance, with 12.6% of the agricultural land having experienced major negative changes. This negative balance is associated with the increase of the area dedicated to vineyards, the transformation of old traditional vineyard plantations to modern trained plantations and to the removing of conservation practices to adopt plots to crop mechanisation. This leads to an unsustainable viticulture and soil degradation in medium- to long-term periods.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Soil erosion; Land use changes; Conservation practice changes; RUSLE; GIS
1. Introduction
During the last two decades, different studies have revealed the importance of soil erosion in the Med-iterranean basin under distinct land use/cover condi-tions by measuring inter-rill and rill erosion on runoff plots (Giordano and Marchisio, 1991; Poesen and Hooke, 1997; UsoÂn, 1998). In comparison with other
typical crops in the Mediterranean region, land use for vineyards results in the highest soil losses: 47± 70 Mg haÿ1
per year in NW Italy (Tropeano, 1983), 35 Mg haÿ1
per year in the mid-Aisne region (France) (Wicherek, 1991), 34 Mg haÿ1
per year in an extreme rainfall event in the SE France (Wainwright, 1996) and 22 Mg haÿ1
per year in the PenedeÁs±Anoia region (NE Spain) (UsoÂn, 1998).
Despite the importance of vineyards in the Medi-terranean region, and particularly in Spain (Spain has the maximum land devoted to viticulture of any country in the world with 1 198 680 ha in 1995 (MAPA, 1997)), and its impact on soil erosion, little
*Corresponding author. Tel.:34-973702615;
fax:34-973702613.
E-mail address: [email protected] (J.A. MartõÂnez-Casasnovas).
research has been focussed on this problem until recently (Wicherek, 1991). The research has mainly concentrated on measuring soil losses by inter-rill and rill erosion on a runoff plot scale. Less research has been devoted to study the problem at larger scales (hillslope and catchment), that have been argued as being fundamental for determining and/or predicting the effects of climate and land use changes on soil erosion.
The objective of this paper is to assess the impact that the intensi®cation of agriculture during the last four decades (in areas mainly dedicated to viticulture in the Mediterranean environment) has had on soil erosion.
2. Methods and materials
The research was carried out in a sample catchment of 2450 ha located in the PenedeÁs±Anoia vineyard region (NE Spain). The area is located about 30± 40 km southwest of Barcelona. It is part of the PenedeÁs Tertiary Depression, that includes calcilu-tites (marls) with occasional sandstones and con-glomerates. The mean annual rainfall ranges from 471 to 670 mm (Porta et al., 1994), with high intensity rainstorms during autumn (i.e. >100 mm hÿ1
in short periods).
Aerial photographs from 1957 (1:30000 scale) and from 1992 (1:22000 scale) were selected to map the land uses and conservation practices existing in both situations. The 1957 aerial photographs were also used to map contours (10 m interval) by a photogrammetric restitution process, in order to obtain a DEM (25 m spatial resolution) by spatial interpolation in a raster-based GIS. A commercial 25 m resolution DEM was acquired to characterise the topography of the 1992 situation. The estimation of soil losses was made by applying the revised universal soil loss equation (RUSLE) (Renard et al., 1997).
Different land use/cover classes were identi®ed in the study area: (1) traditional vineyard plantations (non-trained vines), (2) modern vineyard plantations (trained vines), (3) rainfed fruit trees (old plantations of apple trees, almond trees, olive trees, peach trees), (4) winter cereals and grassland, (5) shrubland (50± 75% vegetation cover), (6) forest (65±80% vegetation cover), (7) gullies and (8) built-up areas. Several
conservation practice classes were also distinguished: (1) tillage perpendicular to the maximum slope dient, (2) tillage parallel to the maximum slope gra-dient, (3) tillage oblique to the maximum slope gradient, (4) without conservation practices, (5) broadbase terraces and tillage direction perpendicular to maximum slope gradient, (6) broadbase terraces perpendicular to the maximum slope gradient, tillage parallel to the maximum slope gradient, (7) broadbase terraces perpendicular to the maximum slope gradient, tillage parallel to the maximum slope gradient, (8) broadbase terraces perpendicular to the maximum slope gradient, tillage oblique to the maximum slope gradient and (9) bench terraces.
The mean value of theRfactor for the study area was determined from rainfall data corresponding to the period 1950±1992. The equation formulated by ICONA (1988) was used to compute the R factor because of the lack of data to compute the EI30factor of the Wischmeier and Smith (1978) equation. The computed R factor, 2580 MJ haÿ1
per year, was applied to estimate the soil losses in both situations (1957 and 1992). TheKfactor was estimated accord-ing to the method of Wischmeier and Smith (1978) adapted by RoÈmkens et al. (1997). The required soil information was extracted from the soil information system of the PenedeÁs±Anoia (MartõÂnez-Casasnovas, 1998), derived from a soil survey carried out between 1991 and 1992. Due to the lack of soil information for the 1957 situation, the same K factor values were used. The slope factor (LS factor) was estimated using the equation formulated by Moore and Wilson (1993). The respective 1957 and 1992 DEM were used to compute the LS factor by means of GIS operations. TheCfactor was calculated according to the method proposed by Wischmeier and Smith (1978) and i®ed by Dissmeyer and Foster (1981). Those mod-i®cations consider different covering periods according to the crops or vegetation stage. The P factor was estimated on the basis of the tillage direc-tion with respect to the maximum slope gradient and the presence of speci®c conservation practices (ter-races).
3. Results and discussion
3.1. Changes in land use/cover and conservation practices
Signi®cant changes occurred in the land use/cover during studied period (Table 1). Changes occurred by 55.6% of the study area. The most important were in the classes winter cereals and grassland, modern vineyard plantations and built-up areas. The area covered by traditional vineyard plantations decreased by 5%. Modern vineyard plantations appeared as a consequence of crop mechanisation. In 1992, this class represented 7.5% of the total study area. The overall balance of area devoted to vineyards
(tradi-tional or modern plantations) indicates an increase of 2.5% of the total study area.
Regarding the conservation practices, an important part of the agricultural land did not have conservation practices in place at the considered dates: 39.3% in 1957 and 40.3% in 1992 (Table 2). The main con-servation practices were broadbase terraces and til-lage perpendicular to the maximum slope gradient (33.4% of the agricultural land in 1957 and 28.5% in 1992). This tandem is considered as the most effective conservation measure of the ones identi®ed in the study area (Porta et al., 1994). Important changes affected the most protective management practices: the area with broadbase terraces and tillage perpen-dicular to the maximum slope gradient decreased by Table 1
Matrix of changes of land use/cover occurred between 1957 and 1992 in the Rierussa catchment (number of hectares)
Land use/cover classes in 1992 Land use/cover classes in 1957 Total for 1992
(1) (2) (3) (4) (5) (6) (7) (8)
(1) Traditional vineyard plantations 179.5 0 22.3 273.8 13.2 10.9 11.8 0 511.5 (2) Modern vineyard plantations 74.2 0 4.4 92.9 1.1 6.1 4.1 0 182.8
(3) Rainfed fruit trees 60.3 0 11.4 71.9 1.1 4.7 4.2 0 153.6
(4) Winter cereals and grassland 163.9 0 18.7 291.1 6.4 19.8 12.9 0 512.8
(5) Shrubland 31.6 0 6.9 46.8 1.7 7.0 5.3 0.3 99.6
(6) Forest 36.5 0 5.3 58.4 3.5 52.0 11.3 0 167.0
(7) Gullies 25.4 0 2.9 50.5 5.3 4.9 540.3 0.2 629.5
(8) Built-up areas 62.0 0 15.9 84.3 8.3 5.9 4.8 12.3 193.5
Total for 1957 633.4 0 87.8 969.7 40.6 111.3 594.7 12.8 2450.3
Table 2
Matrix of changes of conservation practices between 1957 and 1992 in the Rierussa catchment (number of hectares)
Conservation practices in 1992 Conservation practices in 1957 Total for 1992 (1) (2) (3) (4) (5) (6) (7) (8)
(1) Tillage perpendicular to m.s.g.a 5.0 2.2 0 56.9 53.6 6.1 4.9 60.0 188.7
(2) Tillage parallel to m.s.g. 0.1 1.1 0 14.7 30.5 1.9 0 14.6 62.9
(3) Tillage oblique to m.s.g. 0 0 1.2 1.5 0.9 0.2 0 10.4 14.2
(4) Without conservation practices 7.9 4.6 1.0 233.5 145.4 19.4 3.7 183.1 598.6 (5) Broadbase terraces and tillage perpendicular to m.s.g. 8.1 0.1 1.2 121.9 187.5 10.6 4.6 130.6 464.6 (6) Broadbase terraces and tillage parallel to m.s.g. 0.5 0 0 21.7 16.8 4.4 1.7 19.6 64.7 (7) Broadbase terraces and tillage oblique to m.s.g. 2.7 0 0 16.3 21.3 1.1 3.8 7.6 52.8
(8) Terraces 1.9 0.3 0 53.8 76.4 1.0 1.1 46.3 180.8
(9) Other land uses 0 0.7 0 75.9 85.8 5.7 1.0 52.4 221.5
Total for 1957 26.2 9.0 3.4 596.2 618.2 50.4 20.8 524.6 1848.8
4.9%, the area with row direction parallel to the maximum slope gradient increased by 3.5%, and the area with tillage perpendicular to the maximum slope gradient without terraces increased by 10.3%. Those changes were made to favour the mechanisa-tion of some vineyard plantamechanisa-tions by achieving longer vine rows. The overall result of the changes in conservation practices in the studied period is a decrease of the plots with terraces (broadbase and bench terraces) in 18.5% of the agricultural land in 1992.
3.2. Soil loss and soil loss changes
The result of the application of the RUSLE for both situations is shown in Fig. 1. The analysis of those data reveals a clear pattern of changes characterised by a decrease of the area with very low to moderate soil losses and an increase of the area with moderately high to very high soil losses from 1957 to 1992. The agricultural land with soil loss >100 Mg haÿ1
per year increased signi®cantly from 10.8 to 25.0%. The land use/cover changes with the highest impact on soil loss in 1992 were the transformations from winter cereals or grassland to vineyard plantations (traditional or modern) or to rainfed tree plantations. Those occurred
in 26.9% of the agricultural land in 1992. The trans-formations from traditional vineyard plantations to modern vineyard plantations or to rainfed tree planta-tions, that occurred in 8.3% of the agricultural land, also had high impact on the increase of soil loss (Tables 1 and 3).
Regarding the changes on conservation practices, the highest negative impact, was the removal of terraces (broadbase or bench terraces). This occurred on 32.8% of the agricultural land (Table 2). A net increase of soil loss occurred in 44.1% of this area, and 15.6% experienced a diminution (Table 3). The intro-duction of new terraces provided an improvement in the soil loss balance in part of the study area. This type of change was carried out on 14.0% of the agricultural land (Table 2). However, in some cases, use of tillage parallel or oblique to the maximum slope gradient increased soil losses.
The soil loss balance shows that 12.6% of the agricultural land experienced major negative changes in a period that comprises 35 years after the advent of mechanisation. This leads to an unsustainable viticul-ture and to soil degradation in the study area in medium-term, specially when the perspective is a progressive transformation of plots with traditional cultivation to mechanised cultivation.
Table 3
Relationships between the main land use/cover and conservation practices changes and the soil loss changes (percentages with respect to total changes)
<ÿ100 to 50% ÿ50 to 50% 50 to >300% Total
Main land use/cover changes
From traditional vineyard plantations to modern vineyard plantations or rainfed tree plantations
2.1 4.3 3.9 10.4
From traditional vineyard plantations to winter cereals or grassland 3.2 5.7 3.8 12.7 From winter cereals or grassland to vineyards or rainfed tree plantations 7.0 13.1 13.7 33.9 From winter cereals or grassland to shrubland or forest 2.2 4.9 1.1 8.1 From traditional vineyard or rainfed tree plantations to other uses 9.8 12.1 2.6 24.6 From shrubland, forest or gullied areas to other uses 0.5 4.9 4.9 10.3
Total 24.9 44.9 30.2 100.0
Main conservation practices changes
Changes that imply the removing of terraces 6.0 15.6 17.0 38.6
Changes that imply the loss of other soil conservation measures 2.7 5.2 4.8 12.7
Changes that imply the introduction of terraces 6.4 6.5 2.4 15.3
Changes that imply the introduction of other soil conservation measures 3.1 8.9 9.2 21.1
Other changes 4.4 3.4 4.3 12.1
4. Conclusions
The present paper has shown the importance of the impact of human intervention regarding land use/ cover and conservation practice changes on soil erosion, in an agricultural area of fundamental con-cern in the Mediterranean region. The applied meth-odology, based on GIS analysis of multitemporal data, made it possible to locate the areas where soil loss changes exist as well as to obtain a quantitative estimation of those changes. It has also been useful to con®rm whether changes in the land use/cover and/or in the conservation practice structures in the region affected soil erosion at the catchment scale. The main cause of soil erosion increase in the study area is the uncontrolled transformation of old vine-yard plantations and other land uses to modern plantations. Those transformations are mainly car-ried out to facilitate the mechanisation of vineyards. The transformations usually involve the removal of conservation practices that, in many cases, are not reinstalled after the levelling of the terrain or are not correctly designed. The results obtained should prevent the successive transformations to new vineyard plantations that are being carried out in the study area, as well as in the Mediterranean region.
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