Central Spanish Pyrenees Research Articles

Pyrenean meadows in Natura 2000 network: grass production and plant biodiversity conservation

In semi-natural mountain meadows, yield and forage quality must be reconciled with plant biodiversity conservation. This study was performed to analyze the relationships between these three parameters. To quantify plant biodiversity and pastoral value (PV), phytosociological inventories were performed in 104 semi-natural meadows in the Central Spanish Pyrenees included in the Natura 2000 network. Forage yields were calculated and forage samples were analyzed for relative feed value (RFV). We identified two main types of meadows: (i) those that had “more intensive management,” relatively close to farm buildings, with little or no slope, dominated by grasses, with low plant biodiversity, high PV and yield, but low forage quality and (ii) those that had “less intensive management,” distant from farm buildings, on slopes, richer in “other forbs”, with high plant biodiversity and forage quality, but low PV and yield. Conservation policies should emphasize less intensive management practices to maintain plant diversity in the semi-natural meadows in the Pyrenees. The widespread view that “other forbs” have low nutritional value should be revised in future research. These species often are undervalued by the PV method, because their nutritional quality, digestibility and intake are poorly understood.

Mapping the annual evolution of snow depth in a small catchment in the Pyrenees using the long-range terrestrial laser scanning

This paper presents the methodology used to develop snow depth distribution maps for a small catchment in the Central Spanish Pyrenees covering 55 ha in a 1:10,000 scale. The Main Map was obtained using LiDAR (light detection and ranging) technology from a long-range Terrestrial Laser Scanner (TLS) in six field surveys undertaken during the 2012 winter–spring period. This technique enabled the acquisition of information at a very high resolution concerning the spatial variability of snow cover, providing snow depth information for remote areas where data acquisition is complex and hazardous. We describe the methodological steps and the quality assessment applied in developing the maps. Comparison with manual measurements confirmed the reliability of the snow depth maps, including areas located at large distances from the scanner (800 m). This method provides a promising tool for future investigations of snow dynamics in mountainous environments.

A proposal for avalanche susceptibility mapping in the Pyrenees using GIS: the Formigal-Peyreget area (Sheet 145-I; scale 1:25.000)

The aim of this work is to show a proposal for avalanche susceptibility mapping (scale 1:25.000) using Geographic Information Systems (GIS). The map to which the article accompanies (Formigal; Sheet 145-I) follows strictly the dimensions of the Spanish Topographic Cartography series at scale 1:25.000. The Formigal-Peyreget area, located in the Central Spanish and French Pyrenees, is one of the Pyrenean regions where avalanche risk is more noticeable. The methodology involves the use of GIS to model avalanche starting zones, including the multi-criteria cateogorisation of four variables: (i) minimum altitude of the regional isotherm of 0°C for the winter months; (ii) slope; (iii) ground cover; (iv) morphology of the slope (curvature). The information presented in the map classifies avalanche start zones susceptibility into four categories: low, moderate, high and very high. This methodology is intended to be used as a reference for the production of future maps of avalanche susceptibility in other regions where the method is deemed appropriate.

Impact of climate and land use change on water availability and reservoir management: Scenarios in the Upper Aragón River, Spanish Pyrenees

Streamflows in a Mediterranean mountain basin in the central Spanish Pyrenees were projected under various climate and land use change scenarios. Streamflow series projected for 2021–2050 were used to simulate the management of the Yesa reservoir, which is critical to the downstream supply of irrigation and domestic water. Streamflows were simulated using the Regional Hydro-Ecologic Simulation System (RHESSys). The results show that increased forest cover in the basin could decrease annual streamflow by 16%, mainly in early spring, summer and autumn. Regional climate models (RCMs) project a trend of warming and drying in the basin for the period 2021–2050, which will cause a 13.8% decrease in annual streamflow, mainly in late spring and summer. The combined effects of forest regeneration and climate change are expected to reduce annual streamflows by 29.6%, with marked decreases affecting all months with the exception of January and February, when the decline will be moderate. Under these streamflow reduction scenarios it is expected that it will be difficult for the Yesa reservoir to meet the current water demand, based on its current storage capacity (476hm3). If the current project to enlarge the reservoir to a capacity of 1059hm3 is completed, the potential to apply multi-annual streamflow management, which will increase the feasibility of maintaining the current water supply. However, under future climate and land cover scenarios, reservoir storage will rarely exceed half of the expected capacity, and the river flows downstream of the reservoir is projected to be dramatically reduced.

Comparative analysis of the response of various land covers to an exceptional rainfall event in the central Spanish Pyrenees, October 2012

ABSTRACTThe hydrological and geomorphological effects of an exceptional rainstorm event that occurred in the central Spanish Pyrenees during 19–21 October 2012 were studied in five experimental catchments under various land covers: (i) subhumid badlands; (ii) dense forest; (iii) an abandoned farmland area recolonized by shrubs and forest patches; and (iv) subalpine grasslands. Hydrographs and sedigraphs demonstrated that vegetation cover is a major factor affecting the control of floods even during exceptional rainstorms, at least at the spatial scale at which the phenomenon was studied (catchment sizes: 0.3–2.8 km2) and under dry catchment conditions. The combined precipitation over the two days (c. 250 mm) was the greatest for any two‐day event recorded since 1950 in the central‐western Pyrenees for all but one of the stations in the study. Five pulses of most intense rainfall were recorded. The forested catchment did not react to the two most intense rainfall pulses, because of the very low antecedent level of the water table. The main peak flow occurred only when at least a part of the catchment was saturated. The abandoned farmland catchment had two small peak discharges at the beginning of the event, which were produced by infiltration excess overland flow from eroded areas close to the main stream. During the third most intense rainfall period a large part of this catchment contributed to runoff and a relatively high peak discharge was produced. The badland catchment reacted immediately from the beginning of the rainstorm, yielding very high discharges accompanied by high suspended sediment concentrations. The subalpine catchment showed a hydrograph mirroring the hyetograph, with brief but intense hydrological responses to increased precipitation, because of the marked gradients and the presence of bare rock in the headwaters. A high volume of bedload was carried during the peak discharge. Copyright © 2013 John Wiley & Sons, Ltd.

Changes in Land Use of Pyrenean Mountain Pastures — Ski Runs and Livestock Management — Between 1972 and 2005 and the Effects on Subalpine Grasslands

In recent decades, the use of some subalpine mountain grasslands in the Central Spanish Pyrenees has changed. Ski resorts have been developed and cattle herd management has shifted from the traditional “rotational-type” system in which grazing cattle are overseen by a herder to a “continuous-type” system that does not involve a herder. In 2005, the locations of 30 floristic inventories performed in 1972 were revisited and inventories were repeated in two adjacent similar areas, although one had been used for the development of ski runs and the other had not. The objective was to assess the effects of those changes on plant diversity and other characteristics of the grasslands. In both areas, plant diversity was significantly higher in 2005 than it was in 1972. Both areas had been grazed by cattle to a similar extent; thus, the results suggest that diversity was affected primarily by the change in the livestock grazing system. Livestock grazing within the skiing area appears to have counterbalanced any reduction in plant diversity that would have occurred because of the construction and use of ski runs. In the skiing area, legume cover and pastoral value decreased, the Ellenberg Nitrogen Index reflected lower soil nutrients available to plants, and the cover of plant species that regenerate by seeds increased between 1972 and 2005; such changes did not occur in the non-skiing area. The abundance of ruderal species increased more in the skiing area than in the non-skiing area. Between 1981 and 2000, the amount of bare ground increased only in the skiing area.

The Middle and Upper Devonian conodont sequence from La Guardia D’Àres Sections (Spanish Central Pyrenees)

The Middle and Upper Devonian conodont sequence from La Guardia D’Àres Sections (Spanish Central Pyrenees)

Eifelian (Middle Devonian) to Lower Frasnian (Upper Devonian) conodont biostratigraphy in the Villech section (Spanish Central Pyrenees)

Eifelian (Middle Devonian) to Lower Frasnian (Upper Devonian) conodont biostratigraphy in the Villech section (Spanish Central Pyrenees)

Cartografía de zonas probables de salida de aludes en el Alto Gállego (Pirineo Central Aragonés) mediante el empleo de Sistemas de Información Geográfica

We present in this work the cartography of probable avalanche starting zones in the Alto Gállego valley (Spanish central Pyrenees) made by using a Geographical Information System (ArcGIS). The conditioning factors used to generate the general model for probable avalanche starting zones (MGZPSA) were: altitude of the monthly regional 0ºC isotherm (December-April), slope and surface cover. The additional incorporation of the monthly solar radiation variable allowed to classify these areas into three susceptibility sectors according to the radiation inputs and their subsequent contribution to the instability of the snowpack (solar radiation model; MRSZPSA). The two models were validated using two control areas with contrasted aspect located in the high sector of the valley.

Factores en la variabilidad espacial de los cambios de cubierta vegetal en el Pirineo

Mediterranean mountain areas show during the twentieth century intense revegetation processes, mainly characterised by the advance of forests and shrubs. This is explained by land abandonment and the noticeable decrease of the livestock pressure on the pastures. This paper analyses the influence of some physical and human factors on the intensity and spatial patterns of the revegetation processes in the Borau valley (Central Spanish Pyrenees) between 1957 and 2000. About 45% of the study area showed important modifications in the vegetation cover. The succession processes toward more mature vegetation stages are dominant (41.5%). On the contrary, the retreat toward less mature vegetation stages affects small sectors (3.5%). Low and middle slopes covered by abandoned fields were the areas in which the main changes were observed. Nevertheless, the advance towards more mature vegetation stages was moderate, since the 25.8% of the area only advanced one stage, the 14.3% showed an advance of two stages and only the 1,4% of the territory showed an advance of more than two stages. Livestock pressure and terrain exposure, which determine the solar incoming radiation, were the most important factors to explain the spatial differences in the land cover change. On the contrary, other topographic variables play a secondary role, although other studies have shown their important influence at more detailed spatial scales.

Soil moisture changes after land abandonment in the Central Spanish Pyrenees

The European mountainous areas, such as the Pyrenees, have suffered important land use changes since the beginning of the XX century. These changes affect the plant cover recovery process and then the runoff and sediment production. Soil moisture can be a key factor in the evolution of the abandoned land. It determines the vegetation recovery, runoff generation, sediment detachment and soil development through runoff and infiltration processes. This paper aims to study the influence of land-use and seasonality on soil moisture. Measurements were carried out weekly during 1997 and 1998 by means of the Time Domain Reflectrometry method. The selected land-uses were: Cereal (fertilised and with artica management), Fallow, Meadow, Abandoned (after fertilised cereal and artica management), Burnt (two plots under different post-fire recovery conditions), and the Control plot, which is a dense Scrubland. The results show that land-use is a key factor in the seasonal and spatial variability of soil moisture. The scrubland, meadow and fallow plots showed always a higher water content ( 30 % of soil moisture mean annual value), meanwhile the abandoned land stored less water (23 %). Burnt, artica and cereal plots had intermediate values. Seasonally, summer used to be the driest period as year 1998 confirmed. Nevertheless the year 1997 was extremely wet during summer due to the high rainfall values. Soil moisture was always higher than 10 %, even during the driest periods. Previous weekly rainfall and antecedent soil moisture explain 80 % of the variability. No relationship was found between the soil moisture changes and the variability amongst plots throughout the studied period.

Diferencias espaciales en la evolución del NDVI en la cuenca alta del Aragón : efectos de los caminos en el uso del suelo

The vegetation cover evolution in the central Spanish Pyrenees is analysed from 1993 to 2000. The analysis has been achieved using one NDVI (Normalized Vegetation Index) temporal series obtained from NOAA-AVHRR images. A positive trend in NDVI data has been detected. However, the spatial differences in the magnitude and sign of NDVI trends are significant. An important increment of vegetation biomass is detected in most areas, particularly in those affected by field abandonment and extensive land use (shrublands and pine forests). Cultivated fields and pastures above timberline show a smaller increase in vegetation cover. The results indicate the important role of socio-economic transformations and land-use extensification in the vegetal biomass evolution.

Coladas de piedras (debris flows) y dinámica fluvial en ríos torrenciales del Pirineo Central : el caso del río Ijuez

Debris flows and fluvial dynamics in torrential rivers of Central Pyrenees. A great accumulation o heterometric deposits is studied in the headwater of the Ijuez river, Central Spanish Pyrenees, triggered by successive debris flows. The granulometric and sedimentological characteristics of the depositare analyzed and they are compared with the fluvial-type sedúnents, located downstream. Some aspects of the influence of these deposits on the general dynamics of the main river are discussed.

La gestión de los usos del suelo como estrategia para mejorar la producción y la calidad del agua : resultados experimentales en el Pirineo Central español

Different land-uses and plant covers yield a wide range of overland flow and sediment concentration. In the 'Aísa Valley" Experimental Station, located in the Central Spanish Pyrenees, information has been obtained on the hydromorphological functioning of both actual and traditional land-uses, confirming that farmland abandonment in steep slopes and the expansion of meadows and shrub cover represent a decrease in bothsediment yield and water availability at a basin scale. With this in mind the authors discuss possible land-use changes that contribute to improve the quality of water resources.

Procesos geomórficos históricos y su relación con la actividad humana en el Pirineo central español

The Central Spanish Pyrenees show a great diversity of geomorphic processes in relation with topographic and climatic heterogeneity and according to the strong altitudinal gradient. Human activity in the last millenniums has contributed to disturb the original landscape and its hydromorphological dynamics: the upper forest belt was eliminated by means of Jire during the Middle Age, in order to enlarge the extent of summer pastures; and the hillslopes located under 1600 m were cultivated in heavy topographic conditions, being frequently burnt in order to improve the quality of pastures. At present, evidences of this human activity are visible everywhere; in the subalpine belt mass movements and dense rill networks caused the loss of many soils and the expansion of gelifluxion terracettes; in middle mountain, overland flow has much increased the soil surface stoniness, and debris flows of different size have developed on the hillslopes and on the river channels. Rivers show a strong torrentiality, prevailing unstable channels and coarse sediment transport. The authors apport information on some historical geomorphic processes, related with human activity.

Modeling shrub encroachment in subalpine grasslands under different environmental and management scenarios

Woody plants are spreading in many alpine and subalpine ecosystems and are expected to continue increasing in response to land abandonment and global warming. This encroachment threatens species diversity, and considerable efforts have been deployed to control it. In this study, we combined a lattice model and field data to investigate the efficiency of different management strategies in controlling shrub encroachment in alpine grasslands. The model parameter values were estimated in the field based on the thorny shrub Echinospartum horridum (erizón) which is currently encroaching in central Spanish Pyrenees. Our study shows that encroachment could accelerate if climate warming continues. Different management scenarios consisting of a gradient of livestock pressures, fire events and mechanical removal were simulated to identify scenarios able to control the expansion of shrubs into grasslands. Our study shows that grazing alone cannot stop encroachment. Rather, a combination of grazing and shrub removal (either by fire or mechanical removal) is needed, and our model can help estimate the frequency and intensities of the shrub removal. This model can be used to investigate the consequences of different management scenarios and environmental variability which could be of practical value in the preservation of alpine grasslands.

2D viscoplastic finite element modelling of slow landslides: the Portalet case study (Spain)

This paper proposes a hydro-geomechanical finite element model to reproduce the kinematic behaviour of large slow landslides. The interaction between solid skeleton and pore fluids is modelled with a time dependent u–pw formulation and a groundwater model that takes into account recorded daily rainfall intensity. A viscoplastic constitutive model based on Perzyna’s theory is applied to reproduce soil viscous behaviour and the delayed creep deformation. The proposed model is applied to Portalet landslide (Central Spanish Pyrenees). This is an active paleo-landslide that has been reactivated by the construction of a parking area at the toe of the slope. The stability analysis reveals that, after the constructive solutions were undertaken, the slope is in a limit equilibrium situation. Nevertheless, time-dependent analysis reproduces the nearly constant strain rate (secondary creep) and the acceleration/deceleration of the moving mass due to hydrological changes. Overall, the model reproduces a 2-m displacement in the past 8 years that coincides with in situ monitoring data. The proposed model is useful for short- and mid-term predictions of secondary creep. However, long-time predictions remain uncertain, stability depends strongly on the position of the water table depth and new failures during tertiary creep due to soil temporal microstructural degradation are difficult to calibrate.

Sediment balance in four catchments with different land cover in the Central Spanish Pyrenees

Sediment balance in four catchments with different land cover in the Central Spanish Pyrenees

Multi-sensor advanced DInSAR monitoring of very slow landslides: The Tena Valley case study (Central Spanish Pyrenees)

In this work it is demonstrated how the combination of multi-sensor and multi-temporal SAR data improves the monitoring capacity of very slow landslides. The study area is the Upper Tena Valley (Central Spanish Pyrenees), where mostly very slow earth flows, have caused direct damage estimated at approximately 15M€ in the last decade. The advanced DInSAR processing of ascending orbit ALOS PALSAR images (2006–2010) and descending orbit ERS & Envisat (2001–2007) and TerraSAR-X (2008) datasets, has provided heterogeneous displacement velocity measurements. The projection along the steepest slope of LOS displacements reduces the geometrical differences introduced by each satellite. These results were compared and validated with available D-GPS measurements. In a second step PS displacement data are combined with a landslide inventory, increasing the number of monitored landslides with sufficient PS from 4% to 19%, obtained from C- and X-band data, to 38% of the total (294). Finally, the retrieved multi-sensor landslides velocities are classified with respect to the magnitude of road damages that occurred in the 2008–2010 period. At local scale, the combination of multi-sensor data was useful to differentiate different landslide displacement directions, to measure different velocity patterns within the same moving mass, and to distinguish the slower (natural) and faster (human induced) landslides. The analysis of displacement time series permitted to evaluate the acceleration caused by a destabilising anthropogenic change, and the correlation between displacement variability and seasonal precipitation and melting.

Small scale spatial variability of snow density and depth over complex alpine terrain: Implications for estimating snow water equivalent

This study analyzes spatial variability of snow depth and density from measurements made in February and April of 2010 and 2011 in three 1–2km2 areas within a valley of the central Spanish Pyrenees. Snow density was correlated with snow depth and different terrain characteristics. Regression models were used to predict the spatial variability of snow density, and to assess how the error in computed densities might influence estimates of snow water equivalent (SWE).The variability in snow depth was much greater than that of snow density. The average snow density was much greater in April than in February. The correlations between snow depth and density were generally statistically significant but typically not very high, and their magnitudes and signs were highly variable among sites and surveys. The correlation with other topographic variables showed the same variability in magnitude and sign, and consequently the resulting regression models were very inconsistent, and in general explained little of the variance. Antecedent climatic and snow conditions prior to each survey help highlight the main causes of the contrasting relation shown between snow depth, density and terrain. As a consequence of the moderate spatial variability of snow density relative to snow depth, the absolute error in the SWE estimated from computed densities using the regression models was generally less than 15%. The error was similar to that obtained by relating snow density measurements directly to adjacent snow depths.