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Massif Central (massif + central)
Selected AbstractsAn AFLP clock for the absolute dating of shallow-time evolutionary history based on the intraspecific divergence of southwestern European alpine plant speciesMOLECULAR ECOLOGY, Issue 4 2009MATTHIAS KROPF Abstract The dating of recent events in the history of organisms needs divergence rates based on molecular fingerprint markers. Here, we used amplified fragment length polymorphisms (AFLPs) of three distantly related alpine plant species co-occurring in the Spanish Sierra Nevada, the Pyrenees and the southwestern Alps/Massif Central to establish divergence rates. Within each of these species (Gentiana alpina, Kernera saxatilis and Silene rupestris), we found that the degree of AFLP divergence (DN72) between mountain phylogroups was significantly correlated with their time of divergence (as inferred from palaeoclimatic/palynological data), indicating constant AFLP divergence rates. As these rates did not differ significantly among species, a regression analysis based on the pooled data was utilized to generate a general AFLP rate. The application of this latter rate to AFLP data from other herbaceous plant species (Minuartia biflora: Schönswetter et al. 2006; Nigella degenii: Comes et al. 2008) resulted in a plausible timing of the recolonization of the Svalbard Islands and the separation of populations from the Alps and Scandinavia (Minuartia), and of island population separation in the Aegean Archipelago (Nigella). Furthermore, the AFLP mutation rate obtained in our study is of the same magnitude as AFLP mutation rates published previously. The temporal limits of our AFLP rate, which is based on intraspecific vicariance events at shallow (i.e. late glacial/Early Holocene) time scales, remains to be tested. [source] Landscape composition and vole outbreaks: evidence from an eight year study of Arvicola terrestrisECOGRAPHY, Issue 6 2000E. Fichet-Calvet This study investigates the relationships between landscape composition and the population dynamics of the fossorial water vole Arvicola terrestris. Land use patterns were studied based on agricultural and forestry data from the French Ministry of Agriculture collected in 1955 and 1988. In the Massif Central, France, water vole populations were monitored from 1985 to 1993 by using index methods. Outbreaks of water vole populations occurred in many dispersed epicentres and spread suddenly and widely over > 7500 km2. At a regional scale, the fluctuation lasts six years on average with an outbreak period lasting from two to three years. Density variation patterns are positively correlated with the proportion of permanent grassland to agricultural land. A high risk of outbreak is linked to a high proportion of permanent grassland (over 90%), whereas a low risk of outbreak is linked to a proportion of < 80%, Conversely, density variation patterns are negatively correlated with the proportion of temporary grassland to agricultural land and with the proportion of forest to total land in the western (major) part of the study area. Temporary grassland thus appears to be a marginal habitat for water voles and extensive forests could act as a brake on outbreaks. The increase in the area of permanent grassland from 1955 to 1988 was apparently the major cause of chronic high densities of water voles. Therefore, land use and landscape management could be one way to control water vole outbreaks. [source] Community composition and activity of prokaryotes associated to detrital particles in two contrasting lake ecosystemsFEMS MICROBIOLOGY ECOLOGY, Issue 3 2006Charles Lemarchand Abstract The composition, distribution and extracellular enzyme activities of bacteria attached to small (2,50 ,m in size) transparent exopolymer and Coomassie-stained proteinaceous particles (TEP and CSP) were examined in two lakes of different trophic status located in the Massif Central of France. TEP concentrations (104,106 particle per L) were significantly higher in the more productive lake and were significantly related to chlorophyll a concentrations. The majority of TEP and CSP were colonized by bacteria that constituted 2.6% and 7.4% of the total 4,,6-diamidino-2-phenylindole-stained bacteria in lakes Pavin and Aydat, respectively. In both lakes, the composition of particle-associated bacteria was different from that of free-living bacteria, the Betaproteobacteria and Bacteroidetes (i.e. former Cytophaga,Flavobacteria group) being the dominant groups on particles. We also found that 2,5 ,m TEP were more colonized than 2,5 ,m CSP in the two lakes, and that TEP colonization was higher in the less productive lake. Measurements of Leucine aminopeptidase and ,-glucosidase activities in fractionated lake water (0.2,1.2, 1.2,5 and >5 ,m fractions) indicated that proteolytic activity was always higher and that particle-associated bacteria have higher enzymatic activities than free-living bacteria. The glycolytic activities in the 1.2,5 and >5 ,m fractions were related to the abundance of TEP. We conclude that small freshwater detrital organic particles constitute microhabitats with high bacterial activities in pelagic environments and, undoubtedly, present significant ecological implications for the prokaryotic community structure and function in aquatic ecosystems. [source] Origin of deep saline groundwaters in the Vienne granitic rocks (France): constraints inferred from boron and strontium isotopesGEOFLUIDS (ELECTRONIC), Issue 2 2001J. Casanova Abstract As part of a preliminary geological characterization programme to assess the feasibility of an underground laboratory in granitic rock, a series of 17 deep boreholes (maximum depth, 900 m) was drilled by ANDRA in the Vienne district, France. A salinity gradient was demonstrated in the granitic waters with concentrations varying from approximately 1 g L,1 at 150 m depth at the top of the basement (beneath the sedimentary cover) to 10 g L,1 in the deeper part (from 400 to 600 m depth). Sr and B isotope ratios were measured in order to better understand the origin of the salinity and to evaluate the degree of water,rock interaction in the system. The results obtained were compared to those of mineral spring waters emerging from the granitic basement in the Massif Central. Evidence in support of a significant marine contribution include: (i) the Cl,Br investigations agree with a marine origin for the saline groundwaters without evolution from seawater; (ii) the 87Sr/86Sr ratio of the Vienne deep groundwaters (0.7078,0.7084) is in agreement with a palaeo-seawater isotopic signature; (iii) measured ,11B values for the deepest brine samples are enriched in 11B (up to 36.1,) relative to the granitic springs. The combined use of ,11B, Cl, B, Br, Sr contents and 87Sr/86Sr ratios makes it possible to define and quantify a mixing model between marine and crustal end-members in order to explain the origin of the deep saline groundwaters in the Vienne granitic rocks. [source] Analyses of the stress field in southeastern France from earthquake focal mechanismsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2001Emmanuel Baroux Summary Owing to the apparent deformation field heterogeneity, the stress regimes around the Provence block, from the fronts of the Massif Central and Alpine range up to the Ligurian Sea, have not been well defined. To improve the understanding of the SE France stress field, we determine new earthquake focal mechanisms and compute the present-day stress states by inversion of the 89 available focal mechanisms around the Provence domain, including 17 new ones calculated in the current study. This study provides evidence of six distinct deformation domains around the Provence block, with different tectonic regimes. On a regional scale, we identify three zones characterized by significantly different stress regimes: a western one affected by an extensional stress (normal faulting) regime; a southeastern one characterized by a compressional stress (reverse to strike-slip faulting) regime with NNW- to WNW-trending ,1; and a northeastern one, namely the Digne nappe front, marked by a NE-trending compression. Note that the Digne nappe back domain is controlled by an extensional regime that is deforming the western Alpine core. This extensional regime could be a response to buoyancy forces related to the Alpine high topography. The stress regimes in the southeast of the Argentera Massif and around the Durance fault are consistent with a coherent NNW-trending ,1, implying a left-lateral component of the active reverse oblique slip of the Moyenne Durance Fault. In the Rhone Valley, an E-trending extension characterizes the tectonic regime, implying a normal component of the present-day N,^mes fault displacement. This study provides evidence for short-scale variation of the stress states, which arises from abrupt changes in the boundary force influences on upper crustal fragments (blocks). These spatial stress changes around the Provence block result from the coeval influence of forces applied at both its extremities, namely in the northeast the Alpine front push, and in the southeast the northward African plate drift. In addition to these boundary forces, the mantle plume under the Massif Central influences the western block boundary. [source] Exploitation of High-Yields in Hard-Rock Aquifers: Downscaling Methodology Combining GIS and Multicriteria Analysis to Delineate Field Prospecting ZonesGROUND WATER, Issue 4 2001Patrick Lachassagne Based on research work in the Truyàre River catchment of the Massif Central (Lozàre Department, France), a methodology has been developed for delineating favorable prospecting zones of a few square kilometers within basement areas of several hundred, if not thousand, square kilometers for the purpose of siting high-yield water wells. The methodology adopts a functional approach to hard-rock aquifers using a conceptual model of the aquifer structure and of the functioning of the main aquifer compartments: the alterites (weathered and decayed rock), the underlying weathered-fissured zone, and the fractured bedrock. It involves an economically feasible method of mapping the thickness and spatial distribution of the alterites and the weathered-fissured zone, on which the long-term exploitation of the water resource chiefly depends. This method is used for the first time in hydrogeology. The potential ground water resources were mapped by GIS multicriteria analysis using parameters characterizing the structure and functioning of the aquifer, i.e., lithology and hydrogeological properties of the substratum, nature and thickness of the alterites and weathered-fissured zone, depth of the water table, slope, fracture networks and present-day tectonic stresses, and forecasted ground water quality. The methodology involves a coherent process of downscaling that, through applying methods that are increasingly precise but also increasingly costly, enables the selection of sites with diminishing surface areas as the work advances. The resulting documents are used for ground water exploration, although they can also be applied to the broader domain of land-use management. [source] Two contrasted P,T,time paths of coronitic metanorites of the French Massif Central: are reaction textures reliable guides to metamorphic histories?JOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2005C. NICOLLET Abstract Metanorites from two eclogitized metagabbros of the Hercynian French Massif Central preserve coronitic textures of hornblende, garnet, quartz and/or kyanite produced at the expense of the primary magmatic assemblage orthopyroxene and plagioclase. Using a petrogenetic grid in the CFMASH system, two possible P,T evolutions for the origin of the coronas are evaluated. The sequence of reactions involving the formation of Hbl (,Ky) ± Grt and Qtz coronitic assemblages is consistent with an isobaric cooling at high pressure (c. 1,2 GPa) under hydrated conditions. However, this P,T path, inferred by using only petrographical observations, is inconsistent with the geochronological constraints: emplacement of the gabbro at 490 Ma and high-pressure metamorphism at 410 Ma. In order to reconcile petrographical observations with geochronological constraints, we propose a discontinuous two-stage evolution involving a change in water activity with time. (1) Emplacement and cooling of the norite at low pressure under anhydrous conditions, at 490 Ma. (2) During the Hercynian orogeny, the norite experienced an increase in pressure and temperature under fluid-present conditions. Adding water to the system implies a dramatic change in the petrogenetic grid topology, restricting the orthopyroxene,plagioclase assemblage only to high temperatures. Therefore, the breakdown of the unstable magmatic assemblage, through apparent retrograde reactions, occurred along the prograde P,T path which never crossed the equilibrium boundaries of these reactions. [source] Indirect facilitation and competition in tree species colonization of sub-Mediterranean grasslandsJOURNAL OF VEGETATION SCIENCE, Issue 3 2006Georges Kunstler Abstract: Questions: In the absence of herbivores, what is the importance of shrub facilitation for the colonization of grasslands by Fagus sylvatica and Quercus pubescens? Is there an indirect facilitative effect of shrubs on tree seedlings by limiting herb competition? Location: Causse du Larzac, southern Massif Central, France. Methods: We conducted field experiments on the facilitative role of shrubs in seedling emergence and survival, in relation to potential negative effects of shading and the presence of herbs. The effects of shade and herbs on allocation and root morphology were analysed in a pot experiment. Results: According to these experiments, the establishment of both tree species was facilitated by shrubs, but the two species differed in the processes underlying this facilitation. Shade directly facilitates the emergence rate of both species. Shade also indirectly facilitates Fagus survival by limiting herb competition. No indirect facilitation of Quercus survival was detected. These differences reflect variation in the tolerance of herb competition by seedlings of the two species. The tolerance of herb competition by Quercus seedlings allows regeneration over a wide area under each shrub and some regeneration events in grasslands at low grazing intensity. In contrast, for Fagus, only a narrow area under each shrub is suitable; regeneration is zero in grassland. The high tolerance of herb competition by Quercus seedlings may result from the avoidance of root competition. Conclusions In grasslands with severe drought stress, and almost obligatory shrub facilitation for tree seedling regeneration, the tolerance of herb competition may alter the precise role of facilitation in the colonization process. [source] Metals, Salt, and Slaves: Economic Links Between Gaul and Italy From the Eighth to the Late Sixth Centuries BCOXFORD JOURNAL OF ARCHAEOLOGY, Issue 3 2003Daphne Nash Briggs Summary. This paper discusses the role of metals, salt, textiles, and slaves in the development of networks of reciprocal exchange that interlinked the élites of Etruscan Italy and Early Iron Age Gaul between the eighth and sixth centuries BC. Maritime and transalpine contact are considered separately. Certain regional specialisms in Gaul are discussed: metals in the west and centre, supporting prosperous HaD élites around the rim of the Massif Central, salt on coasts and in the east, perhaps in exchange for Italian textiles, and slaves perhaps especially from the sixth-century BC Aisne,Marne/Mont Lassois complex. A principal point is to establish the ubiquity and economic importance of women and children as domestic slaves both in Italy and Gaul and their consequent significance as valuable objects of élite exchange. Development in patterns of slave procurement during this period are considered. [source] | |||||||||||||