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International audience; Increased drought frequency and severity may reshape tree species distribution in arid environments. Dioecious tree species may be more sensitive to climate warming if sex-related vulnerability to drought occurs, since lower performance of one sex may drive differential stress tolerance, sex-related mortality rates and biased sex ratios. We explored the effect of sex and environment on branch hydraulic (hydraulic conductivity and vulnerability to embolism) and trunk anatomical traits in both sexes of the dioecious conifer Juniperus thurifera L. at two sites with contrasting water availability. Additionally, we tested for a trade-off between hydraulic safety (vulnerability to embolism) and efficiency (hydraulic conductivity). Vulnerability to embolism and hydraulic conductivity were unaffected by sex or site at branch level. In contrast, sex played a significant role in xylem anatomy. We found a trade-off between hydraulic safety and efficiency, with larger conductivities related to higher vulnerabilities to embolism. At the anatomical level, females' trunk showed xylem anatomical traits related to greater hydraulic efficiency (higher theoretical hydraulic conductivity) over safety (thinner tracheid walls, lower Mork's Index), whereas males' trunk anatomy followed a more conservative strategy, especially in the drier site. Reconciling the discrepancy between branch hydraulic function and trunk xylem anatomy would require a thorough and integrated understanding of the tree structure-function relationship at the whole-plant level. Nevertheless, lower construction costs and higher efficiency in females' xylem anatomy at trunk level might explain the previously observed higher growth rates in mesic habitats. However, prioritizing efficiency over safety in trunk construction might make females more sensitive to drought, endangering the species' persistence in a drier world.

International audience; Many studies have reported that hydraulic properties vary considerably between tree species, but little is known about their intraspecific variation and, therefore, their capacity to adapt to a warmer and drier climate. Here, we quantify phenotypic divergence and clinal variation for embolism resistance, hydraulic conductivity and branch growth, in four tree species, two angiosperms (Betula pendula, Populus tremula) and two conifers (Picea abies, Pinus sylvestris), across their latitudinal distribution in Europe. Growth and hydraulic efficiency varied widely within species and between populations. The variability of embolism resistance was in general weaker than that of growth and hydraulic efficiency, and very low for all species but Populus tremula. In addition, no and weak support for a safety vs. efficiency trade-off was observed for the angiosperm and conifer species, respectively. The limited variability of embolism resistance observed here for all species except Populus tremula, suggests that forest populations will unlikely be able to adapt hydraulically to drier conditions through the evolution of embolism resistance.

[EN] Flash floods represent one of the most common natural hazards in mountain catchments, and are frequent in Mediterranean environments. As a result of the widespread lack of reliable data on past events, the understanding of their spatio-temporal occurrence and their climatic triggers remains rather limited. Here, we present a dendrogeomorphic reconstruction of past flash flood activity in the Arroyo de los Puentes stream (Sierra de Guadarrama, Spanish Central System). We analyze a total of 287 increment cores from 178 disturbed Scots pine trees (Pinus sylvestris L.) which yielded indications on 212 growth disturbances related to past flash flood impact. In combination with local archives, meteorological data, annual forest management records and highly-resolved terrestrial data (i.e., LiDAR data and aerial imagery), the dendrogeomorphic time series allowed dating 25 flash floods over the last three centuries, with a major event leaving an intense geomorphic footprint throughout the catchment in 1936. The analysis of meteorological records suggests that the rainfall thresholds of flash floods vary with the seasonality of events. Dated flash floods in the 20th century were primarily related with synoptic troughs owing to the arrival of air masses from north and west on the Iberian Peninsula during negative indices of the North Atlantic Oscillation. The results of this study contribute considerably to a better understanding of hazards related with hydrogeomorphic processes in central Spain in general and in the Sierra de Guadarrama National Park in particular., This study has been partially funded by the projects IDEA-GesPPNN-163/2010 (OAPN - Organismo Autonomo de Parques Nacionales, Ministerio de Agricultura, Alimentacion y Medio Ambiente) and CGL2010-19274 (projects MAS Dendro-Avenidas) of the Spanish Ministry of Economy and Competitiveness. The authors sincerely acknowledge Marco Borga and other anonymous reviewer. Special recognition must be given to CENEAM, Montes de Valsain, OAPN and JCyL for providing information for this study. Specifically, they want to thank Javier Dones (Director of Montes de Valsain), Ramzi Touchan and Dave Meko for their support during the study, as well as Andres Diez and Gerardo Benito and all participants of the Tree-ring summer school carried out in 2012 in Valsain (Touchan et al., 2013). R. Sanchez-Salguero thanks the financial support from University of Cordoba-Campus de Excelencia Internacional-ceiA3.

Badlands and gullied areas are among those geomorphic environments with the highest erosion rates worldwide. Nevertheless, records of their evolution and their relations with anthropogenic land transformation are scarcer. Here we combine historical data with aerial photographs and tree-ring records to reconstruct the evolution of a badland in a Mediterranean environment of Central Spain. Historical sources suggest an anthropogenic origin of this badland landscape, caused by intense quarrying activities during the 18th century. Aerial photographs allowed detection of dramatic geomorphic changes and the evolution of an emerging vegetation cover since the 1960s, due to widespread reforestation. Finally, tree-ring analyses of exposed roots allowed quantification of recent channel incision of the main gully, and sheet erosion processes. Our results suggest that reforestation practices have influenced the initiation of an episode of incision in the main channel in the 1980s, through the hypothesized creation of disequilibrium in water-sediment balance following decoupling of hillslopes from channel processes. These findings imply an asymmetry in the geomorphic response of badlands to erosion such that in the early evolution stages, vegetation removal results in gullying, but that reforestation alone does not necessarily stabilize the landforms and may even promote renewed incision.

International audience; Among the multiple forms of freshwater pelagic cyanobacteria, the phycoerythrin-rich species Planktothrix rubescens is well adapted to temperate, deep and large lakes. In Lake Geneva, this filamentous and microcystin-producing species has been the dominant cyanobacterial species observed since the early years of this century. In addition to the trophic state (e.g., the phosphorus level), the influences of air and water temperature on the occurrence and development of cyanobacteria are particularly relevant in the context of global climate change. The latter may indeed be particularly marked for lakes in the Alpine region, with a rate of warming that may be twice as large as the global average. The impact of climate change on P. rubescens is thus an important challenge and it has been analysed in this study through two different approaches: (1) the extreme air temperature events as a proxy for future climate and (2) the multi adaptive regression splines (MARS) model to predict future P. rubescens biomass. These methods allowed us to determine whether Lake Geneva will still sustain an important biomass of P. rubescens in forthcoming years, provided there is no severe over-enrichment with nutrients in the future. The outcomes strongly suggest that the fraction of cyanobacterium could increase with respect to the total phytoplankton community by as much as 34 % by the end of this century and induce a significant change in the microalgal composition. Additionally, the results point to the fact that spring is a key period during which air temperature and nutrients become the determinant factors for outbreaks of this species in the subsequent seasons.; > Les bactéries prédatrices obligatoires d'autres bactéries, les bactéries nécessitant une cellule proie Gram négatif afin de compléter leur cycle cellu-laire, appartiennent au groupe polyphylétique des Bdellovibrio et organismes apparentés (BALO). Bien que les interactions entre les bactéries prédatrices et les bactéries proies soient complexes, on commence à comprendre leur dynamique et leur impact sur les communautés bactériennes dans l'environ-nement. Les BALO ont des cycles de vie particuliers : ils grandissent soit de manière épibiotique, quand le prédateur reste attaché à l'enveloppe de sa proie, la division cellulaire étant alors binaire, ou il se déve-loppe dans le périplasme de la cellule proie. Dans ce cas, un prédateur génère plusieurs cellules. Le cycle de vie périplasmique exprime des motifs d'expres-sion géniques et protéiques ainsi que des réseaux de signalisation uniques. Cette revue explore quelques particularités de l'écologie et de la biologie cellu-laire des BALO, ainsi que leurs applications poten-tielles dans les domaines médicaux, agricoles et environnementaux. < organisms (BALO) qui inclue divers groupes monophylétiques : le genre Micavibrio et les familles Bdellovibrionaceae, Bacteriovoraceae et Peridibacteraceae [2]. Ces BALO ont pour cible des bactéries Gram négatif. La pression de prédation, pouvant conduire à la sélection de proies génétiquement résistantes, et l'existence de défenses phénoty-piques et de nature transitoire, qui constituent un mécanisme d'amor-tissement, assurent, in fine, à la fois la survie du prédateur et la capa-cité de la proie à se reconstituer [3, 4]. La dynamique des relations de type proie-prédateur entre bactéries s'avère donc complexe. S'ajoute à cette complexité, la nature mal définie du type d'interaction possible entre organismes (synergique, antagoniste, etc.). Cependant, les nouvelles technologies de séquençage, de bio-informatique et de microscopie, mais aussi le développement d'outils de manipulation génétique, permettent, aujourd'hui, une étude détaillée des méca-nismes cellulaires qui font d'une bactérie, un prédateur obligatoire. Elles offrent également une approche plus large de l'étude de leur impact écologique. Ces connaissances ouvrent de nouvelles voies vers leur application en agriculture, en aquaculture, dans la préservation de notre environnement et en médecine. Cette revue est l'occasion de synthétiser une partie des connaissances actuelles sur les BALO. Le monde méconnu des BALO On sait aujourd'hui que les BALO sont très largement distribués au sein de la biosphère et sont présents aussi bien dans les océans, les mers, les eaux côtières, les estuaires, les rivières, les lacs, que dans les bassins d'aquaculture, les stations d'épuration, l'eau d'irrigation, ou encore dans les sols, les rizières, la rhizosphère et même dans les Les bactéries constituent quantitativement le groupe dominant des organismes cellulaires. En leur sein, les bactéries prédatrices d'autres bactéries ont été très largement sous-estimées comparativement à l'action des virus ou d'autres prédateurs ou parasites euca-ryotes (flagellés, cillés, champignons). Cela est en partie dû à ce que ces bactéries ne constituent pas des populations majeures en terme d'abondance quand les bactériophages, des virus infectant les bactéries, eux, peuvent atteindre des densités dix fois supérieures aux populations bactériennes [1]. Les bactéries prédatrices obligatoires de bactéries (c'est-à-dire dépendantes de la prédation pour se reproduire) sont regroupées dans un groupe polyphylétique 1 appelé Bdellovibrio and like 1 Se dit d'un groupe composé de taxons n'ayant en commun que des convergences adap-tatives et n'ayant pas d'ancêtre commun, contrairement aux groupes monophylétiques.

The indirect effects of aerosol are particularly important over regions where meteorological conditions and aerosol content are favourable to cloud formation. This was observed during the Intensive Cloud Aerosol Measurement Campaign (IMPACT) (European Integrated project on Aerosol Cloud Climate and Air quality Interaction (EUCAARI) project) in the Benelux Union during May 2008. To better understand this cloud formation variability, the indirect effects of aerosol have been included within the WRF-CHIMERE online model. By comparing model results to the aircraft measurements of IMPACT, to surface measurements from EMEP and AIRBASE and to MODIS satellite measurements, we showed that the model is able to simulate the variability and order of magnitude of the observed number of condensation nuclei (CN), even if some differences are identified for specific aerosol size and location. To quantify the impact of the local anthropogenic emissions on cloud formation, a sensitivity study is performed by halving the surface emissions fluxes. It is shown that the indirect radiative effect (IRE) at the surface is positive for both shortwave and longwave with a net warming of +0.99 W/m2. In addition, important instantaneous changes are modelled at local scale with up to &plusmn, 6 &deg, C for temperatures and &plusmn, 50 mm/day for precipitation.

International audience; On forested paths, dendrogeomorphology has been demonstrated to represent a powerful Vincent Jomelli* tool to reconstruct past activity of avalanches, an indispensable step in avalanche hazard Delphine Grancher* assessment. Several quantitative and qualitative approaches have been shown to yield Markus Stoffel † ‡ reasonable event chronologies but the question of the completeness of tree-ring records remains debatable. Here, we present an alternative semi-quantitative approach for the Christophe Corona † determination of past snow avalanche events. The approach relies on the assessment of Daniel Brunstein* the number and position of disturbed trees within avalanche paths as well as on the Nicolas Eckert § and intensity of reactions in trees. In order to demonstrate that no bias was induced by the dendrogeomorphic expert, we carry out a statistical evaluation (Classification and Regres-Michael Deschatres § sion Trees, or CART) of the approach. Results point to the consistency and replicability *Laboratoire de Géographie Physique, of the procedure and to the fact that the approach is not restricted to the identification of Université Panthéon-Sorbonne, UMR high-magnitude avalanches. Evaluation of the semi-quantitative approach is illustrated on 8591 CNRS, 1 place Aristide Briand, Fa well-documented path in Chamonix, French Alps. For the period 1905-2010, comparison 92195 Meudon cedex, France †Dendrolab.ch, Institute of Geological between the avalanche years recorded in a substantial database (Enquête Permanente sur Sciences, University of Berne, les Avalanches, or EPA) and those defined with dendrogeomorphic techniques shows that Baltzerstrasse 1 ‫ם‬ 3, CH-3012 Berne, the avalanche record reconstructed from tree-ring series contains 38% of the observed Switzerland events.

International audience; In snow-rich areas, snow avalanches endanger settlements and cause heavy damage to infrastructure or transportation routes. In wooded avalanche paths, dendrogeomorphology has been used extensively to reconstruct snow avalanche histories or to complement existing archival records. Several authors noted (i) that avalanche chronologies reconstructed from tree rings would depend on the number of trees sampled, and on (ii) the minimum number of tree-ring responses; and (iii) that they would always represent minimum frequencies. These restrictions gave rise to the question of how much of the realavalancheactivity can be captured in tree-ring records. We therefore performed a dendrogeomorphic analysis based on 175 Larix decidua Mill. and 34 Picea abies (L.) Karst. trees from an extensively and accurately documented (1905-2010) avalanche path located in the Arve valley (French Alps) to obtain optimal thresholds for sample size and index values (i.e. percentage of responses in relation to the number of trees alive for a given year). Results clearly demonstrate that a sample size of ~ 100 trees is needed to obtain the best match between reconstruction (tree rings) and documentation (archives) while minimizing the inclusion of noise in the dendrogeomorphic record. Validation of the reconstruction (1771-2010) with historical archives shows that 13 undocumented events could be added to the archival record and that 43% of all documented events were deciphered with dendrogeomorphic techniques. The reconstruction of the spatial extent and reach of past snow avalanches matches with historical archives as far as the longitudinal extent of the largest avalanches is concerned. Yet, tree-ring records tend to underestimate runout elevations for a majority of minor events. Large discrepancies are also reported between the lateral limits derived with dendrogeomorphic techniques and the data reported in historical reports and hazard maps, with tree-ring data suggesting larger lateral spread of avalanche snow.

Hydrogeomorphic processes are a major threat in many parts of the Alps, where they periodically damage infrastructure, disrupt transportation corridors or even cause loss of life. Nonetheless, past torrential activity and the analysis of areas affected during particular events remain often imprecise. It was therefore the purpose of this study to reconstruct spatio-temporal patterns of past debris-flow activity in abandoned channels on the forested cone of the Manival torrent (Massif de la Chartreuse, French Prealps). A Light Detecting and Ranging (LiDAR) generated Digital Elevation Model (DEM) was used to identify five abandoned channels and related depositional forms (lobes, lateral levees) in the proximal alluvial fan of the torrent. A total of 156 Scots pine trees (Pinus sylvestris L.) with clear signs of debris flow events was analyzed and growth disturbances (GD) assessed, such as callus tissue, the onset of compression wood or abrupt growth suppression. In total, 375 GD were identified in the tree-ring samples, pointing to 13 debris-flow events for the period 1931–2008. While debris flows appear to be very common at Manival, they have only rarely propagated outside the main channel over the past 80 years. Furthermore, analysis of the spatial distribution of disturbed trees contributed to the identification of four patterns of debris-flow routing and led to the determination of three preferential breakout locations. Finally, the results of this study demonstrate that the temporal distribution of debris flows did not exhibit significant variations since the beginning of the 20th century.

International audience; P>1. Capturing the relative influence of landscape composition and configuration in real landscapes remains a challenge. Cost-distance modelling provides an interesting approach to the assessment of landscape complexity in a functional way. However, resistances allotted to landscape elements in cost-distance modelling frequently remain defined on the basis of expert advice. To overcome this weakness, we computed resistance coefficients without a priori knowledge through a calibration/validation method enabling us to test the impact of the matrix heterogeneity on the occurrence of the common toad Bufo bufo, the cycles of which imply migrations between complementary habitats. 2. We used cost-distance modelling to elaborate an integrative parameter of landscape composition and configuration in the form of a potential movement zone. We first applied a calibration procedure that systematically tested different resistance values for each landscape element with a large data set. The robustness of the calibrated resistances was then evaluated using two supplementary validation data sets from contrasted landscapes. Finally, in order to isolate the relative influence of landscape configuration, we compared the predictive power of the calibrated potential movement zone with that of landscape composition only. 3. The landscape matrix strongly influences common toad occurrence: selected resistances were low for forests and meadows and intermediate to high for crops. Within the two validation data sets, the potential movement zone was positively and significantly related to toad occurrence and had a better predictive power than landscape composition. 4. Synthesis and applications. This study provides a tool to manage landscape structure in accordance with the ecological requirements of amphibian populations, especially habitat complementation. This method has minimal biological information requirements and therefore could be widely used to investigate the crucial influence of landscape composition and configuration on a broad range of species, and to design functional ecological networks.