Northeast Iberia Research Articles

Diet of wild boar Sus scrofa L. and crop damage in an intensive agroecosystem

The Middle Ebro Valley (MEV) is a semiarid area in northeast Iberia where the original riparian ecosystems are almost extinct and were replaced by intensive irrigated agricultural lands. To minimize crop damages and to understand the impact of wild boar on relict riparian ecosystems, a culling program was undertaken from 1994 until 2004. To assess the impact of wild boars, we analyzed stomach contents and surveyed crop damage. In the MEV, wild boars feed mainly on crops, particularly, maize. Other elements of the diet that are of agricultural origin include wheat, barley, and alfalfa, which are the alternatives to maize in the period between harvest and seeding, which is the basis of seasonal changes in diet. Results indicate that wild boar actively selected maize crops and consumed wheat in proportion to its abundance; barley and alfalfa fields were damaged less than expected based on their abundance. In the MEV, the wild boar population is limited by the availability of shelter areas found in the scarce riparian ecosystems, which do not provide important food items for this population. We conclude that in the region of this study, wild boars are not a significant threat to the flora and fauna of riparian ecosystems, although as these habitats are restored and areas are protected, the carrying capacity for wild boars might increase.

Iberia-Azores Gravity Model (IAGRM) using multi-source gravity data

Abstract A consistent high precision and high resolution gravity model in the north-east Atlantic off Iberia peninsula using multi-source gravity data, ship-borne and satellite derived gravity anomalies, is presented. A solution strategy based on least squares optimal interpolation was used to assimilate into a coherent gravity model, gravity data with different spectral and spatial resolutions. Satellite derived gravity anomalies from KMS02 model, with an error covariance of 25 mGal2, and marine data carefully edited and validated by bias crossover error adjustment, were used in this study. The observation error variance was determined from ship-borne track adjustment and assigned an independent value for each track determined from error variance propagation. Unbiased ship-borne gravity observations were assimilated into the satellite derived gravity KMS02 model by the least squares optimal interpolation algorithm (OI) with bias removed by applying a regional bias to all ship tracks (OI-b) and alternatively by constraining all ship tracks to KMS02 using bias and tilt (OI-t). External error of the model was determined by comparing with recent surveys and it was verified that OI-t approach improved the final gravity model to an accuracy of about 3 mGal. The effect of different merging approaches on geoid solution was also evaluated and it was verified that the merging process can contribute to improve the geoid accuracy up to 4 cm with the OI-t approach.

Modelling the effects of irrigation schemes on the distribution of steppe birds in Mediterranean farmland

Research conducted in several Mediterranean areas indicates that most populations of steppe birds are currently experiencing population declines associated with intensification of traditional agricultural practices. By using habitat suitability modeling (HSM), our aim was to use available environmental data sets, including land use and relief, to model the current distribution of nine steppe bird species in the agriculture dominated areas of the Catalan Ebro basin (northeast Iberia). We then employ HSM to quantitatively assess the future impact of land use changes on the potential distribution range of these species under two scenarios following irrigation of present extensive cereal steppes in the area. HSM analyses showed a close association between steppe bird distribution and the extent of extensive cereal agriculture in flat areas. Although the sensitivity to planned irrigation schemes was species specific, we estimated significant decreases in distribution after irrigation for seven of the nine species examined, i.e. the Little bustard, the Montagu's harrier, the Roller and the Calandra lark, the species predicted to be more severely affected by predicted decreases in area exceeding 50%. Overall, core steppe habitats where most valuable steppe species may co-occur are expected to be mostly impacted and decrease by 74 to 81% after irrigation of only 28 to 36% of the cereal cropland in the region. Future maintenance and survival of viable populations of steppe birds will rely on our ability to enlarge the network of protected areas and to implement agri-environmental measures targeting current species core habitats in low-intensity farmland.

Transgressive–regressive cycles and Jurassic palaeogeography of northeast Iberia

A correlation and sequence stratigraphy study of Jurassic successions has been carried out in the main sedimentary basins of northeast Iberia, i.e., Asturias, Basque-Cantabrian, and Iberian basins, based on the identification of transgressive–regressive cycles. The development and palaeogeographic evolution of the epicontinental carbonate platforms of northeast Iberia were largely controlled by major tectonic activity at three main intervals, at the beginning of the Jurassic, in the Lower–Middle Jurassic transition, and during the uppermost Jurassic, respectively. During Early Jurassic times, northeast Iberia was the site of a single and large carbonate ramp opened to the north. This carbonate ramp suffered a progressive drowning, evolving from an inner to hemipelagic ramp systems, with the local development of suboxic environments in the deepest areas located to the north. During the Middle Jurassic, different open carbonate platforms were formed including the development of swells in intermediate areas. During the Upper Jurassic, the outer ramp areas were progressively moving to the east Iberian Basin, and the ammonite faunas showing a markedly Tethyan affinity thereafter. Three first order T–R cycles bounded by major discontinuities associated with significant time gaps are identified. They extend respectively from the latest Rhaetian to the Early Aalenian, from the Middle Aalenian to the Early Oxfordian and from the Early Oxfordian to the Late Berriasian. Major transgressive peaks occurred at the Middle Toarcian (Bifrons Zone), at the Late Bajocian (upper Niortense and Garantiana zones) and at the mid-Kimmeridgian (Divisum Zone). Each of the first order cycles includes four second-order T–R cycles. Cycles 1.1–1.4 are identified in the northern basins. Cycles 2.1–2.4 display some differences in age of transgressive peaks from one basin to another. Cycles 3.1–3.4 are mainly identified in the Iberian Basin. The correlation with other separated Boreal and Thethysian basins demonstrates that the number and age of T–R cycles varies from one basin to another and are mainly controlled by the local or regional tectonic development. The transgressive peaks may reflect episodes of eustatic rise during the Jurassic. However, their different age from one basin to another is explained by different subsidence evolution.

Maintenance Activities, Technological Knowledge and Consumption Patterns: A View of Northeast Iberia (2000-500 Cal BC)

The analysis of the archaeological evidence from some prehistoric settlements in the area of Valles (northeast Spain) allows us to propose an interpretation of the Late Bronze Age and Early Iron Age in the area as calibrating transformations in the organization of labour, storage patterns and maintenance activities. Despite the difficulties involved in the evaluation of this kind of settlement (pit structures dug into the ground and refilled after use with waste materials), our working assumption is that such deposits contain valuable information concerning the wide variety of activities carried out in the settlements and the dynamics of their development. In our study, it has been possible to hypothesize a continuity it some aspects of production, as well as a marked increase in agrarian production. It is argued that these dynamics can only be understood by focusing on the organization of social activities in the so-called 'domestic domain'.

Palaeogeographical significance of the Triassic-Jurassic unconformity in the north Iberian basin (Sierra del Moncayo, Spain)

Field work carried out on the Lower Jurassic (i.e., Hettangian-lower Pliensbachian) of the north Iberian basin (Sierra del Moncayo, Spain), including the mapping of unconformities and sedimentary units as well as the facies analysis, has allowed us to recognize two episodes in the sedimentary evolution of the basin. A lower one, Hettangian in age, includes sediments deposited during the period of extensional tectonic activity, which involved the formation of half-graben basins by normal listric faults. Sedimentary breccias and rudites, located mainly at the edges of the half-grabens are derived from the erosion of blocks uplifted during the Triassic. In the depocenter of the half-grabens which show most subsidence these breccias pass into thick dolomitic and evaporitic successions, deposited in sabkha environments, under negligible marine influence. The later episode, Sinemurian and lower Pliensbachian in age, consists of shallow marine carbonate units deposited in a low-angle ramp setting. Evaporite accumulation took place during phases of relative lowstand of sea level (i.e., lowstand systems tract), when the basin was cut ooff from open marine conditions; whereas the carbonate sediments mainly represent transgressive and highstand systems tracts. In the Iberian basin, the lowstand episode during the Hettangian was mainly induced by the breakup of the Upper Triassic ramp, which favoured the isolation from open marine conditions of several subsident sub-basins. In addition, it should be noted that the Hettangian is considered as a lowstand sea level episode in some of the proposed global eustatic cycle charts, so that a eustatic component may also be postulated for the isolation of the basin at this time. The infilling of the Hettangian half-grabens left an even topography which was flooded during the Sinemurian sea level rise, leaving shallow carbonate deposits. The results presented here give new information on the paleogeography of northeast Iberia at the Triassic-Jurassic boundary in the context of the opening of the western margin of the Tethys.