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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.

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 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.

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.

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.

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.

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.