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Avances en investigación para la conservación de los páramos andinos

Digital physiotope maps combine multi-source abiotic information, and can be used to assess derived characteristics such as natural hazards and type of forest community. Physiotopes are spatially explicit functional landscape units that stratify landscapes into distinct units, resulting from the interplay between geological, geomorphological and soil processes. Boundaries of the physiotopes in the cuesta landscape of Luxembourg are based on geological boundaries, geomorphological processes boundaries and key indicators of soil forming processes which are supplemented by quantitative topographic land surface parameters such as slope angle. A physiotope map is presented for an area near the village of Bigelbach, which reflects the resource potential of the landscape. We present three derived applications of the physiotope map: a hazard zonation map, a forest community map and a soil erosion vulnerability map. The hazard zonation map is based on weighting and ranking of attributes of the physiotopes, such as process activity, materials, slope angle and forest cover. The derived forest community map strongly reflects the spatial distribution of geological substrate and soils of the main physiotope units along the cuesta. The soil erosion vulnerability map implements the Revised Universal Soil Loss Equation in combination with the physiotope map. The physiotope map content can be extended and updated and its derived products may support landscape conservation and restoration programs, and can be used to monitor temporal changes within a landscape.

Animal activity and litter quality play a key role in forests on decalcified Stein-mergelkeuper marls. The dominant trees hornbeam and beech clearly differ in lit-ter quality, which affects earthworm activity and soil formation. Trees were even more important to topsoil characteristics than the subsoil. Under hornbeam, with high-palatable litter, organic layers were thinner, species richness higher and top-soils wetter and less acidic than under beech with more recalcitrant litter. In decal-cified marl, lateral clay-eluviation leads to differentiation in silty topsoils and clay-rich, water-impermeable Bg-horizons. Depth of the impermeable layer was shallower under hornbeam than under beech. Under hornbeam, formation of silty topsoils is probably counteracted by erosion. High animal activity leads to in-creased denudation of the surface, macropore systems with pipe flow in the soil, and approximately ten times higher export of soil particles than under beech. Un-der the low-palatable beech, leaching can continue without interruption, due to protective litter covers, low macroporosity, and throughflow with loss of base cat-ions and clay particles rather than silt and sand. The two trees also showed habi-tat preferences, which extends their presence in particular habitats beyond the lifespan of individual trees. Hornbeam seedlings were only found under horn-beam, and are probably better adapted to wetness with superficial fine roots. Beech seedlings established everywhere, but further growth may be hampered in wet places due to three dimensional fine root systems. Hornbeam and beech thus act as ecosystem engineers, with different litter quality and animal activity lead-ing to more suitable habitat conditions for themselves, and development of wet and dry subsystems in the forest.

A method to prepare hybrid geomorphological maps of the cuesta landscape in Luxembourg is presented. A hybrid geomorphological map is a combination of a classical geomorphological map and digital geomorphological information layers. The classical maps are hand drawn, utilize symbol-based legends and are printed as paper maps on a 1:10.000 scale. Digital information layers carry geospatial information that is stored in a geodatabase which is managed in a Geographic Information System (GIS). The digital geomorphological information layers include attributes that describe additional information on genesis of landforms, materials composition, process type and process activity, or other conditions. The geomorphological geodatabase serves as a repository for environmental information, which can flexibly be consulted by the end-user, e.g., for planning, land management, hazard assessment, or geoconservation purposes. Two types of geomorphological maps are presented. The first is an overview map on the landscape scale which comprises main units belonging to the cuesta (cuesta plateau and cuesta front), and to the fluvial, mass movement, periglacial, organic, aeolian and the anthropogenic environment. The second type are hybrid geomorphological maps, which here are used to show three detailed characteristic landscapes. These concern a former meander of the Sure near Bettendorf, the transition from the cuesta front to the fluvial landscape near Reisdorf, and a mass movement area along the cuesta front near Wallendorf.

The Attert River basin in Luxembourg is characterised by a large variety of clean and mixed physiogeographical settings (i.e. topography, soil types, land use, bedrock geology, etc.). This in turn generates manifold configurations of rainfall-runoff transformation processes. Here, we provide experimental data from more than a decade of hydro-meteorological observations carried out in a nested catchment set-up, and develop on past and ongoing research on fundamental hydrological functions of catchments: water collection, storage and release. In a first section, we detail the characteristics of the Attert River basin and a set of 9 nested sub-catchments. The second section provides insights into the seasonal and spatial variability of hydrological responses along a wide range of landuse, soil and bedrock settings. The analysis of double-mass curves between precipitation and discharge provided insights into how certain physiogeographic characteristics control hydrological responses. In the third section, we develop on dynamic catchment storage and how it differs between catchments with contrasted landuse and lithology. The fourth section provides insights into the spatial and temporal variability of forest canopy and forest floor storage capacity. Given the considerable amount of precipitation that is intercepted at annual scale, the process is likely to have a substantial influence on catchment storage dynamics.

The knowledge that has been acquired in the project RECONDES on critical conditions necessary for plants and on the occurrence of such conditions in the landscape is used in combination with the analysis of processes to develop strategies that could be applied at critical points and locations, identified by the connectivity mapping, to produce greatest effectiveness of the vegetation measures. This is achieved at the plot and land unit scale based on measurements of plant conditions, and at the catchment scale with the analysis of vegetation cover and conditions, both scales involving identification of erosion hotspots from connectivity mapping and modelling. These results have provided the framework for recommendations on spatial strategies and targeting of revegetation and restoration. The analysis of the effectiveness of different types of plants and species is used to select appropriate plants for different locations in the landscape. This has informed the development of practical guidelines produced for use by land managers and advisors. The research was developed in a Mediterranean environment but has wider applicability to drylands prone to erosion by water.

The knowledge that has been acquired in the project RECONDES on critical conditions necessary for plants and on the occurrence of such conditions in the landscape is used in combination with the analysis of processes to develop strategies that could be applied at critical points and locations, identi ed by the con- nectivity mapping, to produce greatest effectiveness of the vegetation measures. This is achieved at the plot and land unit scale based on measurements of plant conditions, and at the catchment scale with the analysis of vegetation cover and conditions, both scales involving identi cation of erosion hotspots from connectiv- ity mapping and modelling. These results have provided the framework for recom- mendations on spatial strategies and targeting of revegetation and restoration. The analysis of the effectiveness of different types of plants and species is used to select appropriate plants for different locations in the landscape. This has informed the development of practical guidelines produced for use by land managers and advi- sors. The research was developed in a Mediterranean environment but has wider applicability to drylands prone to erosion by water.

This chapter sets out the approach and research methods used to assess the plant types and species that grow in different parts of the targeted Mediterranean landscape and that could potentially be used in restoration strategies and mitigation of desertified and degraded land. Species occurring in the various land units in the study catchment in southeast Spain are identified. These units are reforested land, rainfed croplands, semi-natural and abandoned land and stream channels, Factors restricting growth of trees and understorey vegetation in reforested land were assessed using experimental plots and the effects of pine litter on seed germination were tested. The potential for growth of cover crops between orchard trees was assessed from hydrological balances. Using multivariate statistical analysis various factors were found to influence the regrowth of vegetation in abandoned agricultural lands. In the ephemeral stream channels a wide range of variables was analyzed and presence of species found to be clearly related to substrate and hydrological zone. The results on differential conditions necessary for or favouring growth of various species are used in subsequent design of optimal spatial strategies of planting and restoration.

This book explains the methods and results of a major research project, RECONDES, that was undertaken to develop strategies of effective use of vegetation to combat desertification and land degradation by water. The research approach combined understanding of the processes of erosion and land degradation with identification of suitable and effective plants and types of vegetation that could be used to decrease the intensity of soil erosion. The project uses the relatively new concept of physical connectivity of water and sediment in the landscape. The premise of the approach is that sediment connectivity can be reduced through the development of vegetation in the flow pathways, and that this approach is more sustainable than use of physical structures. It required research into the locations and characteristics of these pathways and into properties of suitable plants and species at a range of scales and land units. These components are combined to produce a spatial strategy of use of suitable plants at the most strategic points in the landscape, designed for restoration or mitigation of land degradation. Additional benefits of use of vegetation as a strategy of sustainable management are outlined. The methods and restoration strategy were developed in relation to the dryland environments of the Mediterranean region of southern Europe, involving field measurements, monitoring and modelling in the study area in Southeast Spain, the driest and most vulnerable region in Europe to desertification.

The context of processes and characteristics of soil erosion and land degradation in Mediterranean lands is outlined. The concept of connectivity is explained. The remainder of the chapter demonstrates development of methods of mapping, analysis and modelling of connectivity to produce a spatial framework for development of strategies of use of vegetation to reduce soil erosion and land degradation. The approach is applied in a range of typical land use types and at a hierarchy of scale from land unit to catchment. Patterns of connectivity and factors influencing the location and intensity of processes are identified, including the influence of topography, structures such as agricultural terraces and check dams, and past land uses. Functioning of connectivity pathways in various rainstorms is assessed. Modes of terrace construction and extent of maintenance, as well as presence of tracks and steep gradients are found to be of importance. A method of connectivity modelling that incorporates effects of structure and vegetation was developed and has been widely applied subsequently.

This book explains the methods and results of a major research project, RECONDES, that was undertaken to develop strategies of effective use of vegetation to combat desertification and land degradation by water. The research approach combined understanding of the processes of erosion and land degradation with identification of suitable and effective plants and types of vegetation that could be used to decrease the intensity of soil erosion. The project uses the relatively new concept of physical connectivity of water and sediment in the landscape. The premise of the approach is that sediment connectivity can be reduced through the development of vegetation in the flow pathways, and that this approach is more sustainable than the use of physical structures. It required research into the locations and characteristics of these pathways and into properties of suitable plants and species at a range of scales and land units. These components are combined to produce a spatial strategy of use of suitable plants at the most strategic points in the landscape, designed for restoration or mitigation of land degradation. Additional bene ts of use of vegetation as a strategy of sustainable management are outlined. The methods and restoration strategy were developed in relation to the dryland environments of the Mediterranean region of southern Europe, involving field measurements, monitoring and modelling in the study area in Southeast Spain, the driest and most vulnerable region in Europe to desertification.

In this chapter the approaches and methods used to measure plant effectiveness in reducing runoff and erosion are explained and results presented for each of the major land units, hillslopes and channels. Evaluations of the properties of plants required are made to inform plant selection for different sites. For use of cover crops in orchards it is important to assess whether the cover crops would have an effect on orchard tree productivity, whilst also reducing soil erosion. A climatic threshold for their use was identified. Soil moisture measurements from different treatment areas and water balance and runoff modelling exercises showed where use of such crops could be beneficial. Extent of vegetation growth on abandoned lands was shown to have a marked effect on runoff, water repellency and soil crusts. Various root parameters were measured on a range of plants and their relation to soil detachment calculated. Differences in root architecture and in orientation of rows of plants were tested. Plant stem density, stem bending and trapping efficiency effects were also assessed experimentally and plant species growing in the Mediterranean study area were grouped according to their erosion control potential. The effects of vegetation and various plant species on roughness, flow hydraulics and sediment trapping in channels were assessed by field measurements and modelling and their resilience to high flow evaluated from observed flood impacts.

The context of processes and characteristics of soil erosion and land deg- radation in Mediterranean lands is outlined. The concept of connectivity is explained. The remainder of the chapter demonstrates development of methods of mapping, analysis and modelling of connectivity to produce a spatial framework for develop- ment of strategies of use of vegetation to reduce soil erosion and land degradation. The approach is applied in a range of typical land use types and at a hierarchy of scale from land unit to catchment. Patterns of connectivity and factors in uencing the location and intensity of processes are identi ed, including the in uence of topography, structures such as agricultural terraces and check dams, and past land uses. Functioning of connectivity pathways in various rainstorms is assessed. Modes of terrace construction and extent of maintenance, as well as presence of tracks and steep gradients are found to be of importance. A method of connectivity modelling that incorporates effects of structure and vegetation was developed and has been widely applied subsequently.

Resumen Este estudio presenta una primera aproximación a la relación entre hidrología,calidad del agua, geología y suelos para un ecosistema de jalca cerca de Cajamarca en el norte de Perú. Debido a que las áreas de jalca son propensas a la degradación de sus suelos húmicos, como resultado del uso del suelo y del cambio climático, se requiere mayor información sobre su hidrología y geoecología. Durante dos campañas de campo se evaluó la geología, geomorfología, suelos y vegetación del área. Además, se realizaron mediciones de conductividad eléctrica hidrológica y se tomaron muestras a lo largo de varias quebradas (arroyos). Aunque en la región hay importantes proyectos mineros, no existe actividad minera en las cuencas estudiadas. Los suelos mostraron una clara relación con su sustrato y en muchos casos tuvieron un alto contenido de materia orgánica, que se demuestra por el predominio de horizontes A mólicos y úmbricos. La hidrología es impulsada por un excedente de agua de alrededor de 300 mm por año y el caudal de los ríos está íntimamente relacionado con la estacionalidad de las lluvias. Hemos encontrado que existe una clara relación entre el sustrato subyacente y la química del agua de los arroyos y pantanos. Se pueden distinguir dos tipos de agua: uno originado de rocas extrusivas dacíticas (ignimbritas), con niveles extremadamente bajos de sólidos disueltos totales, un predominio de Ca2+ y HCO3 -, niveles de sodio relativamente altos y una baja RAS (relación de adsorción de sodio). El otro tipo de agua se origina en zonas de roca madre dominadas por calizas, mostrando niveles mucho más altos de sólidos disueltos totales. La contaminación química del agua, expresada en nitratos y amonio, estuvo relacionada especialmente con zonas pobladas. Abstract This study gives a first approximation of the relationship between hydrology and water quality, geology, and soils for a jalca ecosystem near Cajamarca in Northern Peru. As the jalca areas are prone to degradation of their humic soils as a result of land use and climate change, more information is needed on their hydrology and geoecology. During two field campaigns the area was surveyed with regard to geology, geomorphology, soils, and vegetation. Furthermore, hydrological routings were executed, measuring electrical conductivity (EC25) of stream waters and selectively sampling these waters. Soils showed a clear relationship with their substrate and were in many cases high in organic material as shown by the dominance of mollic and umbric A horizons, respectively. The hydrology is driven by a water surplus of around 300mm per year, and stream discharge is closely related to the seasonality of the rainfall. We found that there is a clear relationship between the underlying substrate and the water chemistry of the streams and fens. Two set of water types can be distinguished: one originating from dacitic extrusive rocks (ignimbrites), with extremely low total dissolved solid levels, a dominance of Ca2+ and HCO3 -, and relatively high sodium levels and with low SAR (sodium adsorption ratio) values. The other type of water originates from limestone dominated bedrock areas, showing much higher total dissolved solid levels. Chemical water pollution, as expressed by nitrates and ammonium, was especially related to settlements.

Resumen Los suelos del páramo almacenan cantidades excepcionales de carbono debido a las condiciones edáficas y climáticas sobre las cuales se desarrollan. Este gran reservorio de carbono está amenazado debido a los efectos del cambio climático y las dinámicas de uso de la tierra. No obstante, el desarrollo de mecanismos de mitigación como los promovidos por REDD+ son una alternativa que puede ayudar a reducir los impactos de estas amenazas y promover su conservación. Sin embargo, para la aplicación de estos tipos de mecanismos es fundamental que los procesos asociados al mantenimiento y dinámica del ciclo del carbono sean comprendidos y los posibles impactos puedan ser proyectados. En este trabajo, a partir de una extensa revisión de artículos indexados, se presenta una síntesis del estado actual del conocimiento y se discute las ventajas y limitaciones de la aplicación de modelos de carbono orgánico del suelo y sus parámetros asociados. Como resultado de esta revisión, concluimos que los modelos disponibles actualmente contienen limitaciones importantes asociados a los procesos y flujos de la descomposición de la materia orgánica que impiden su aplicación en los páramos andinos. Adicionalmente, información sobre las variables de ingreso es limitada y lo mismo aplica para información independiente que permita validar los resultados modelados. El artículo concluye con recomendaciones sobre prioridades futuras de investigación, enfatizando la urgencia del desarrollo de estudios comparativos sobre los efectos del uso de la tierra en la dinámica del carbono, en lugar del desarrollo de estudios experimentales en condiciones controladas. Abstract Paramo soils store exceptionally large amounts of carbon because of the specific edaphic and climatic conditions in tropical high-altitude ecosystems. This soil C-stock is threatened by changes in climate and land use, but potentials for its conservation on the basis of REDD+ type mechanisms are high. However, for application of such mechanisms it is crucial that properties and processes involved are adequately understood and impacts can be predicted. In this paper, an overview is given of the current knowledge and applicability of soil carbon models and parameters involved, based on a full search of publications in international refereed journals. The conclusion is that existing models are not readily applicable to paramo soils because of the specific decomposition processes and pathways. Moreover, information on relevant input parameters is scant and the same holds for data that can be used to validate model outputs. Recommendations are given for future research, emphasizing the urgency of comparative studies of land use impacts, rather than of experimental studies.

Few quantitative experimental studies have been carried out on the influence of subterranean termite activity on the water infiltration capacity of crusted soils in the semi-arid Sahelian region. These studies found increased infiltration rates on soils that were affected by foraging galleries of subterranean termites. In this paper, remarkable results are presented from crusted agricultural fields in the Sanmatenga region in Burkina Faso with clear termite activity compared to reference fields without termite activity. Fine-scale rainfall experiments were carried out and general topsoil (upper 5 cm) characteristics were measured. Infiltration rates were found to be significantly slower on plots affected by subterranean termite activity. These results are contradictory to the findings reported in general literature. On the basis of topsoil property measurements, the reduced infiltration rates cannot be indisputably explained, and we suggest that the main responsible factor for a reduction of infiltration was related to differences in topsoil surface (upper 3 mm) properties. Two hypotheses are formulated in an attempt to explain the reduced water infiltration rates on termite plots.

Landscapes in SE Spain have developed in response to tectonics, climate fluctuations and, more recently, human activity. Fluvial and colluvial sediments such as river terraces and slope deposits found in the valleys reflect a complex interplay between landscape forming processes. Investigating these sediment archives, we reconstructed landscape evolution for the Upper Guadalentín Basin, SE Spain, placing recent erosion processes in a landscape evolution context. Palaeo-lake sediments dated between ~ 17 and ~ 13.8 ka evidence that a Late Glacial lake existed in the area, probably formed by a sudden blockage of the Guadalentín river. Differences in relative height above the floodplain and age between the river terraces of parts of the Guadalentín river indicate that they have not been in equilibrium in the Late Quaternary. Deposition of river terraces along the upstream part of the river is recorded at ~ 13 and ~ 9.5 ka, whereas no evidence of deposition is found for that period along the lower part of the river. There, episodes of sedimentation occur at ~ 7.5–5 ka, ~ 3.4, ~ 1.6, ~ 0.7 and ~ 0.4 ka. This discrepancy is explained by the palaeo-lake and its influence on erosion and sedimentation processes through base level changes. Combining these processes, we propose a schematic model of Late Pleistocene and Holocene landscape evolution. From the model we can conclude that i) the influence of the palaeo-lake on deposition and erosion processes both upstream and downstream is evident; and for the younger river terraces that ii) episodes of deposition seem to coincide in time, but iii) episodes of erosion in between terrace level aggradation do not coincide and neither do terrace level heights and iv) no evidence of deposition is found for the upstream part of the river. Correlation of erosion and sedimentation episodes with climate change and human impact is discussed. Although some correlations can be made, there is strong evidence that climate was not the main driver of landscape processes. We suggest that internal dynamics and local processes are more important drivers for landscape dynamics in the Upper Guadalentín Basin than external and regional factors

Desertification is a major threat in SE Spain and mitigation strategies are required to reduce the adverse effect of water-induced erosion on soil production potential. Severity of soil erosion depends on local runoff response and the connectivity of pathways of water and sediment at different spatial scales. We investigated the connectivity between sources and sinks on semi-natural slopes by means of a semi-distributed model that delineated Hydrological Response Units (HRUs) on the basis of physiographic characteristics. The model was calibrated with information at the plot, hillslope and sub-catchment scale covering the period 1995-2008 and validated against larger events that connected the semi-natural sub-catchment with the underlying cultivated slopes. This approach allowed us to define thresholds at which HRUs transform from sink to source and pathways of water and sediment connect at higher spatial scales. The recognition of the spatio-temporal behaviour of HRUs as sources and sinks is essential for the definition of efficient mitigation strategies that reduce erosion by intervening at strategic points within the catchment. The next step is to improve the skill of the model to reproduce erosive events and deposition over a longer period in the past with more variable meteorological and land cover conditions.

Upscaling vegetation cover for runoff and erosion modeling J.P. Lesschen (1), L.H. Cammeraat (1), A. Meerkerk (2) and B. van Wesemael (2) (1) Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands (lesschen@science.uva.nl), (2) Geography Department, Université Catholique de Louvain, Belgium In semi-arid ecosystems the lack of available water and inter-plant competition leads to sparse vegetation, often resulting in spotted or banded vegetation patterns. As a result of the positive feedback between vegetation and water infiltration soil properties become spatially heterogeneous as well with more organic matter and improved soil physical properties under vegetated patches Consequently, vegetation is the key factor controlling overland flow generation and the distribution of vegetation patches also determines whether runoff becomes connected at the hillslope scale. Runoff and erosion models should therefore include the influence of vegetation, and consequently vegetation patterns have to be scaled up to run these models at catchment scales. At plot scale we described vegetation patterns and erosion pathways and took detailed aerial photographs of vegetation patterns. These images were classified and spatial metrics of these patterns were calculated with FRAGSTATS. We found a linear relationship between fractional vegetation cover and most spatial metrics, which offered us a proxy to upscale vegetation patterns. From a QuickBird image we derived a fractional vegetation cover map using a linear regression that had a R2 of 0.90. At hillslope scale we mapped connectivity patterns after a large rain event in November 2006. These connectivity patterns were compared with the fractional vegetation cover map. The results showed that vegetation largely controls runoff and erosion patterns, not only at the plot scale, but also at the hillslope scale, where 77% of all observed rills were on areas with less than 30% vegetation cover. We used the LAPSUS model to simulate runoff and erosion at the catchment scale and included the fractional vegetation cover map as extra layer to take account for the effect of vegetation patters by adapting the infiltration characteristics. The simulations show more realistic runoff and erosion patterns, because runoff was less connected due to the sink function of the vegetation patches. This demonstrates that erosion models should incorporate the relevant sinks of the hydrological system to prevent overestimation of runoff and erosion at broader scales.

Land degradation due to agricultural land abandonment in Southeast Spain J.P. Lesschen and L.H. Cammeraat Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands (lesschen@science.uva.nl) Land abandonment is nowadays widely spread in Mediterranean countries and is expected to increase, due to changing European policies, urbanisation and climate change. Several studies showed that land degradation will increase after abandonment, especially under semi-arid conditions. The main cause of increased erosion is the absence of ploughing and a slow vegetation recovery, which results in the formation of soil crusts and bare spots with low infiltration rates, leading to more concentrated runoff and gully erosion. To assess the extent and impact of agricultural land abandonment in relation to land degradation we analysed land use, soil properties and erosional processes within a semi-arid catchment in Southeast Spain. Our results showed that soil properties can recover after abandonment to the level of semi-natural shrublands, but this improvement is slow, e.g. only after 40 years of abandonment the soil organic carbon content was comparable to soils under semi-natural vegetation. This means that these fields are especially vulnerable to erosion during the first years after abandonment. Within the study area 17% of the agricultural land was abandoned and more than half of these fields experienced moderate to severe erosion. Gully erosion and piping through terrace walls appeared to be the main erosional processes. From a data set of almost 300 terraces we analysed which factors determined terrace failure. Variables that significantly increased the risk of terrace failure were land abandonment, steeper terrace slope, loam texture, valley bottom position and shrubs on the terrace wall. To mitigate land degradation after abandonment the soil and water conservation practices should focus on reducing the risk of concentrated flow, and revegetation of critical spots in the landscape with indigenous grass species to prevent terrace failure.

Land degradation forms a severe problem in the extensive olive and almond plantations in Southeast Spain. Under rainfed conditions, the canopy cover of these systems is typically below 30%: the soil is frequently tilled to avoid competition for water between the tree crop and weeds and to increase the infiltration capacity. This paper aims to 1) investigate if the water balance of the current almond cropping system allows the growth of cover crops; 2) investigate the frequency, pattern and importance of concentrated flow at the field (2 ha) and catchment scale (4.6 km2) in a case study from Murcia province. Previous studies have shown that evaporation from the plough layer forms the largest water loss of rainfed orchards. In theory, this water can be used to grow a cover crop without competition for water with the trees. Hence, the amount of water available for cover crops was estimated by simulation of the evaporation from the upper 15 cm of the soil with the BUDGET water balance model. First, the model was calibrated for a silt loam soil on marl and a sandy loam soil on slates/phyllites with an average stone content of 47%. Subsequently, the model was run for a normal, wet and dry year, in order to represent the high interannual rainfall variability. The preliminary results show an evaporation loss from the upper 15 cm of the soil of 137-156 mm during the October-March winter period of the ’normal’ year. The evapotranspiration of a shallow rooting cover crop would use a similar amount of water and therefore would not have a negative impact on the growth of the tree crop. At the field scale, the effect of runoff events on the water balance appears to be limited. On average there are 1-3 events a year producing an annual runoff loss of 3-13 mm. Re-infiltration of runoff in the field only affects about 5% of the surface. However, in one field a runoff event of just 2 mm produces an extra water supply of up to 54 mm for the trees on the terrace where the runoff re-infiltrates. Depending on the local climate and agricultural land use, it may be unfeasible to grow cover crops on the entire field. In that case, it is an option to limit vegetation measures to the locations that are most crucial for the hydrological connectivity between fields and land units. Field surveys of concentrated flow were carried out after rain events of different size in order to identify such locations on agricultural land. The results show that roads, terrace access tracks and terraces which are either badly maintained or poorly designed are most crucial for the generation of concentrated flow.

Geomorphological processes in semi-arid environments are strongly influenced by the connectivity between different landscape units. This connectivity can either be established through concentrated flow in rills, gullies and channels but can also have a more diffuse flow character, where sheet flow can reach the channels. Whether connectivity is established or not, is largely dependent on the properties of the landscape units involved. Moreover, the actual connectivity is strongly dependent on the magnitude of the events generating geomorphological processes. From two semi-arid catchments in Southeast Spain examples of events with different degrees of connectivity will be discussed. Fine, intermediate and broad scale aspects will be integrated in relation to the recurrence period of the events and their consequences for runoff generation and sediment delivery at the hillslope and catchment scale will be discussed. This knowledge can be used to apply sustainable strategies to reduce the undesirable on- and off-site effects in order to mitigate land degradation. However, the effectiveness of revegetation and soft engineering approaches are also site specific as well as scale dependent and these aspects should be incorporated in their planning and expected sustainability.

RECONDES is a three-year EU-funded project, which focus is to mitigate desertification processes by means of innovative techniques using vegetation in specific landscape configurations prone to severe degradation processes. One of the research themes is the impact of desertification on abandoned land and potential mitigation practices. Land abandonment is nowadays widely spread in Spain and is expected to increase. Previous research showed that gully erosion was higher on abandoned fields compared to similar cultivated fields. Especially fields that are terraced or have earth dams are prone to gully erosion after abandonment, due to restoration of the natural drainage pattern and piping in case of dispersive substrate. Main cause of increased erosion is the absence of ploughing and a low vegetation recovery, which results in sealing crusts and bare spots with low infiltration rates leading to more runoff and finally gully erosion. The objective of this paper was to analyse the consequences of land abandonment on erosion and to provide effective eco-engineering techniques for mitigation of gully erosion. The study was carried out in the Carcavo basin, a semi-arid catchment in Southeast Spain. At catchment scale all abandoned fields were surveyed and characteristics of each field, gullies and terrace failures were described. One abandoned valley was surveyed at a more detailed scale to create a precise DTM and detailed aerial photographs were taken to study vegetation patterns. The results reveal that gullies on abandoned fields are often located on critical positions at the transition of the hillslope to the channel. This means that when a gully becomes active the connectivity of runoff and sediment in the landscape increases considerably, with the negative off-site effects as a consequence. A reconstruction of eroded sediment from the DTM confirms the importance of gully erosion in terms of sediment losses. Overflow at the lowest point and piping seem to be the main causes of terrace failure. Especially the influence of piping increases in dispersive soils after abandonment, because the topsoil is not ploughed anymore and runoff can enter directly the subsoil through cracks and macro-pores that have been developed after abandonment. Two potential soil and water conservation practices are: (1) Maintenance of terraces and earth dams, as a result more water is retained, which increases the vegetation cover and that strengthens the terrace or earth dam. Only in dispersive soils the risk of piping remains. (2) Revegetation on critical spots in the landscape with indigenous species that grow fast and have dense rooting systems to bind the soil.

SAMENVATTING De discussie over het voorkomen van water op Mars, in vaste of vloeibare vorm, nu en in het verleden, is nog steeds in volle gang. Dat geldt ook voor het effect van mogelijk aanwezig water op de landschapsontwikkeling van de Rode Planeet. Met het vrijkomen van steeds meer nieuwe onderzoeksuitkomsten beginnen zich meer vastomlijnde ideeën te vormen over de rol van water in de geschiedenis van deze interessante planeet.

Abandonment of agricultural land is one of the main changes of land use in Mediterranean countries. From the land use change analysis with the CLUE-S model appeared that especially marl areas without irrigation possibilities are potentially subject to abandonment. However, specifically these areas are most vulnerable for gully erosion, due to dispersion and slaking of marl. The objective of our study was to test if gully erosion was more active on abandoned fields and to model the spatial distribution of potentially vulnerable areas. The study was carried out in the Carcavo basin, a semi-arid catchment in the province of Murcia (SE Spain). Abandoned and agricultural fields with similar topography and lithology were compared with respect to the number and activeness of gullies. At abandoned fields the number of gullies was two times larger than on agriculture fields, especially on abandoned terraced fields gully erosion was occurring frequently. With rainfall simulations the runoff characteristics were compared and this showed that runoff concentration occurred much quicker on the abandoned fields, as a result of crust formation and reduced storage capacity. The change of topsoil characteristics was confirmed by thin section analysis. With a simple GIS-model the potentially vulnerable areas for gully erosion were identified, based on topography, lithology, catchment size, and land use. These predictions enable researchers and engineers to mitigate gully erosion by applying preventive conservation practices.