Résumé
Uncertainties of snowpack models and of their meteorological forcings limit their use by avalanche hazard forecasters, or for glaciological and hydrological studies. The spatialized simulations currently available for avalanche hazard forecasting are only assimilating sparse meteorological observations. As suggested by recent studies, their forecasting skills could be significantly improved by assimilating satellite data such as snow reflectances from satellites in the visible and the near-infrared spectra. Indeed, these data can help constrain the microstructural properties of surface snow and light absorbing impurities content, which in turn affect the surface energy and mass budgets. This paper investigates the prerequisites of satellite data assimilation into a detailed snowpack model. An ensemble version of Météo-France operational snowpack forecasting system (named S2M) was built for this study. This operational system runs on topographic classes instead of grid points, so-called ‘semi-distributed’ approach. Each class corresponds to one of the 23 mountain massifs of the French Alps (about 1000 km2 each), an altitudinal range (by step of 300 m) and aspect (by step of 45°). We assess the feasability of satellite data assimilation in such a semi-distributed geometry. Ensemble simulations are compared with satellite observations from MODIS and Sentinel-2, and with in-situ reflectance observations. The study focuses on the 2013–2014 and 2016–2017 winters in the Grandes-Rousses massif. Substantial Pearson R2 correlations (0.75–0.90) of MODIS observations with simulations are found over the domain. This suggests that assimilating it could have an impact on the spatialized snowpack forecasting system. However, observations contain significant biases (0.1–0.2 in reflectance) which prevent their direct assimilation. MODIS spectral band ratios seem to be much less biased. This may open the way to an operational assimilation of MODIS reflectances into the Météo-France snowpack modelling system.
Auteurs, date et publication :
Auteurs Bertrand Cluzet , Jesus Revuelto , Matthieu Lafaysse , François Tuzet , Emmanuel Cosme , Ghislain Picard , Laurent Arnaud , Marie Dumont
Publication : Cold Regions Science and Technology
Date : 2025
Volume : 170
Pages : 102918
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Sensitivity of grassland biomass production to climate is critical to impacts on multiple ecological processes and ecosystem services. Understanding its climate determinants is essential for climate change adaptation. This requires long-term monitoring, using robust methods that are appropriated by stakeholders. We tested the sensitivity of easily measured sward height to interannual climate variation in mountain grasslands. Using twelve consecutive years of measurements across 67 grassland plots representative of six land-use types associated with different landscape positions, we show that peak green biomass increased with mean summer months (June and July) maximum temperature. Different land-use types responded to specific combinations of climate parameters, but all except higher-elevation summer pastures were sensitive to summer months temperatures. We did not detect any effects of drought, with summer precipitation instead decreasing peak biomass of some grasslands due to cooling and cloudiness, also suggesting that soil water recharge from snowmelt was enough to sustain the first growth cycle. Summer pasture peak biomass decreased with number of frosts during the onset of growth in May. These result support the robustness and sensitivity of sward height as an indicator for climate response of peak fodder biomass. Differential responses across land-use types suggest some resource complementarity which can support tactical adaptation for farmers. During the three recent hottest summers (2015, 2017 and 2018) production was well below predicted values from actual temperatures, suggesting a potential regime shift when the vegetative growth period is shortened by temperature-driven acceleration in phenology and/or heat stress combined with high light intensity causing physiological damage. The baseline regime and the anomalies in hottest years need confirmation for longer time series and across a greater geographic extent. Further effects of drought and of an extended growing season are also likely for post-harvest or grazing regrowth.
Auteurs, date et publication :
Auteurs Karl Grigulis , Sandra Lavorel
Publication : Ecological Indicators
Date : 2025
Volume : 116
Pages : 106519
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Sound radiation patterns have ecological implications in the effective communication between conspecifics, like optimization of the sound propagation, increase the likelihood to reach mates and to mitigate effects of sound scattering by environmental factors like vegetation. The territorial frog Allobates femoralis advertises its territory against conspecific males and attract females with advertisement calls. Here we report the nearly omnidirectional sound-radiation pattern of the advertisement call of A. femoralis. This sound spreading pattern allows the males to attract mates and repel rivals in all directions. Furthermore, A. femoralis males direct the advertisement call to conspecific neighbours after phonotactic orientation.
Auteurs, date et publication :
Auteurs Camilo Rodriguez , Walter Hoedl
Publication : BEHAVIOURAL PROCESSES
Date : 2020
Volume : 170
Catégorie(s)
#ANR-Citation #CNRS #FORET NouraguesRésumé
Background
Previous research has shown diverse vertical space use by various taxa, highlighting the importance of forest vertical structure. Yet, we know little about vertical space use of tropical forests, and we often fail to explore how this three-dimensional space use changes over time.
Methods
Here we use canopy tower systems in French Guiana and passive acoustic monitoring to measure Neotropical bat activity above and below the forest canopy throughout nine nights. We use a Bayesian generalized linear mixed effect model and kernel density estimates to demonstrate patterns in space-use over time.
Results
We found that different bats use both canopy and understory space differently and that these patterns change throughout the night. Overall, bats were more active above the canopy (including Cormura brevirostris, Molossus molossus, Peropteryx kappleri and Peropteryx macrotis), but multiple species or acoustic complexes (when species identification was impossible) were more active in the understory (such as Centronycteris maximiliani, Myotis riparius, Pteronotus alitonus and Pteronotus rubiginosus). We also found that most bats showed temporally-changing preferences in hourly activity. Some species were less active (e.g., P. kappleri and P. macrotis), whereas others were more active (Pteronotus gymnonotus, C. brevirostris, and M. molossus) on nights with higher moon illuminance.
Discussion
Here we show that Neotropical bats use habitat above the forest canopy and within the forest understory differently throughout the night. While bats generally were more active above the forest canopy, we show that individual groups of bats use space differently over the course of a night, and some prefer the understory. This work highlights the need to consider diel cycles in studies of space use, as animals use different habitats during different periods of the day.
Auteurs, date et publication :
Auteurs Dylan G.E. Gomes , Giulliana Appel , Jesse R. Barber , Diogo Provete
Publication : PeerJ
Date : 2025
Volume : 8
Pages : e10591
Catégorie(s)
#CNRS #FORET NouraguesRésumé
Anticipating the genetic and phenotypic changes induced by natural or artificial selection requires reliable estimates of trait evolvabilities (genetic variances and covariances). However, whether or not multivariate quantitative genetics models are able to predict precisely the evolution of traits of interest, especially fitness-related, life-history traits, remains an open empirical question. Here, we assessed to what extent the response to bivariate artificial selection on both body size and maturity in the medaka Oryzias latipes, a model fish species, fits the theoretical predictions. Three populations were selected for divergent body size while maintaining a constant selection pressure against late maturity. The observed evolutionary trends did not match the predictions from a bivariate quantitative genetics "animal" model. The most parsimonious model identified environmental, but not genetic, covariances between both traits, which cannot explain why body size did not evolve in the line selected for a smaller body length. We investigated alternative mechanisms (including genetic drift, inbreeding depression, natural selection, scaling or genetic asymmetry issues, and undetected genetic correlations) but could not attribute the deviation from theory to any single explanation. Overall, these results question the ability of multivariate quantitative models to provide valid and operational predictions of the evolutionary response to multivariate selection on complex traits.
Auteurs, date et publication :
Auteurs Arnaud Le Rouzic , Clémentine Renneville , Alexis Millot , Simon Agostini , David Carmignac , Éric Édeline
Publication : bioRxiv
Date : 2020
Pages : 2020.01.23.916361
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Anthropogenic perturbations such as harvesting often select against a large body size, and are predicted to induce rapid evolution towards smaller body sizes and earlier maturation. However, the evolvability of body size and size-correlated traits remains seldom evaluated in wild populations. Here, we use a laboratory experiment over 6 generations to measure the ability of wild-caught medaka fish (Oryzias latipes) to evolve in response to bidirectional size-dependent selection mimicking opposite harvest regimes. Specifically, we imposed selection against a small body size (Large line), against a large body size (Small line) or random selection (Control line), and measured correlated responses across multiple phenotypic, life-history and endocrine traits. As expected, the Large line evolved faster somatic growth and delayed maturation, but also evolved smaller body sizes at hatch, with no change in average levels of pituitary gene expressions of luteinizing, follicle-stimulating or growth (GH) hormones. In contrast, the Small medaka line was unable to evolve smaller body sizes or earlier maturation, but showed marginally-significant signs of increased reproductive investment (age effect on maturity probability, larger egg sizes, elevated pituitary GH production). Natural selection on medaka body size was too weak to significantly hinder the effect of artificial selection, indicating that the asymmetric body-size response to size-dependent selection reflected an asymmetry in body-size evolvability. Our results show that trait evolvability may be contingent upon the direction of selection, and that a detailed knowledge of trait evolutionary potential is needed to forecast population response to anthropogenic change.
Auteurs, date et publication :
Auteurs Clémentine Renneville , Alexis Millot , Simon Agostini , David Carmignac , Gersende Maugars , Sylvie Dufour , Arnaud Le Rouzic , Eric Edeline
Publication : bioRxiv
Date : 2020
Pages : 498683
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Extreme climatic events (ECEs) such as droughts and heat waves affect ecosystem functioning and species turnover. This study investigated the effect of elevated CO2 on species’ resilience to ECEs. Monoliths of intact soil and their plant communities from an upland grassland were exposed to 2050 climate scenarios with or without an ECE under ambient (390 ppm) or elevated (520 ppm) CO2. Ecophysiological traits of two perennial grasses (Dactylis glomerata and Holcus lanatus) were measured before, during, and after ECE. At similar soil water content, leaf elongation was greater under elevated CO2 for both species. The resilience of D. glomerata increased under enhanced CO2 (+60%) whereas H. lanatus mostly died during ECE. D. glomerata accumulated 30% more fructans, which were more highly polymerized, and 4-fold less sucrose than H. lanatus. The fructan concentration in leaf meristems was significantly increased under elevated CO2. Their relative abundance changed during the ECE, resulting in a more polymerized assemblage in H. lanatus and a more depolymerized assemblage in D. glomerata. The ratio of low degree of polymerization fructans to sucrose in leaf meristems was the best predictor of resilience across species. This study underlines the role of carbohydrate metabolism and the species-dependent effect of elevated CO2 on the resilience of grasses to ECE.
Auteurs, date et publication :
Auteurs Florence Volaire , Annette Morvan-Bertrand , Marie-Pascale Prud’homme , Marie-Lise Benot , Angela Augusti , Marine Zwicke , Jacques Roy , Damien Landais , Catherine Picon-Cochard
Publication : Journal of Experimental Botany
Date : 2020
Volume : 71
Issue : 1
Pages : 370-385
Catégorie(s)
#ANR-Citation #CNRS #Ecotron de MontpellierRésumé
Animals use a variety of strategies to avoid acute dehydration and death. Yet, how chronic exposure to sub-lethal dehydration may entail physiological and fitness costs remains elusive. In this study, we experimentally tested if water restriction causes increased oxidative stress (OS) and telomere length (TL) shortening, two well-described mediators of environment-fitness relationships. We exposed 100 yearling female and male common lizards (Zootoca vivipara) either to a 51-day period of water restriction or to water ad libitum, followed by 45 days in common garden outdoor conditions. We measured the kinetic changes in OS and TL and found that water-restricted males had enhanced antioxidant defences and decreased oxidative damage at day 36, whereas females did not immediately respond. A month and a half after water restriction, both sexes experienced a drop in antioxidant capacity but only males exhibited significant TL shortening. In the following 3 years, we found that lizards with longer initial TL and those who maintained stronger antioxidant defences experienced higher longevity, irrespective of sex and water restriction. Together, these results unravelled sex-specific responses to water restriction, with potential applications in better understanding the physiological costs of increasing summer droughts as a result of global climate change.
Auteurs, date et publication :
Auteurs Andreaz Dupoue , Frederic Angelier , Cecile Ribout , Sandrine Meylan , David Rozen-Rechels , Beatriz Decenciere , Simon Agostini , Jean-Francois Le Galliard
Publication : BIOLOGY LETTERS
Date : 2020
Volume : 16
Issue : 2
Catégorie(s)
#ANR-Citation #CEREEP #CNRS #ENSRésumé
Severe drought and extreme heat associated with the 2015–2016 El Niño event have led to large carbon emissions from the tropical vegetation to the atmosphere. With the return to normal climatic conditions in 2017, tropical forest aboveground carbon (AGC) stocks are expected to partly recover due to increased productivity, but the intensity and spatial distribution of this recovery are unknown. We used low-frequency microwave satellite data (L-VOD) to feature precise monitoring of AGC changes and show that the AGC recovery of tropical ecosystems was slow and that by the end of 2017, AGC had not reached predrought levels of 2014. From 2014 to 2017, tropical AGC stocks decreased by
1.31.21.5
Pg C due to persistent AGC losses in Africa (
−0.9−1.1−0.8
Pg C) and America (
−0.5−0.6−0.4
Pg C). Pantropically, drylands recovered their carbon stocks to pre–El Niño levels, but African and American humid forests did not, suggesting carryover effects from enhanced forest mortality.
Auteurs, date et publication :
Auteurs Jean-Pierre Wigneron , Lei Fan , Philippe Ciais , Ana Bastos , Martin Brandt , Jérome Chave , Sassan Saatchi , Alessandro Baccini , Rasmus Fensholt
Publication : Science Advances
Date : 2020
Volume : 6
Issue : 6
Pages : eaay4603
Catégorie(s)
#ANR-Citation #CNRS #FORET NouraguesRésumé
Plant roots are inhabited by a diversity of microorganisms known to be key drivers of plant growth and health. Although the rules governing root microbiota assembly have been investigated and the importance of abiotic determinants highlighted, the consequences of the biotic context of the plant community have often been overlooked. We tested the hypothesis that the abundance of species in a given plant neighborhood could leave a fingerprint on its root-endophytic fungal community, ultimately impacting its biomass. Outdoor experimental mesocosms, comprising a range of floristic compositions and spatially mapped plant distributions, were monitored for 2y. Medicago truncatula was used as trap-plant and grown under standardized conditions on soil samples collected in the mesocosms. The root-endophytic fungal community of M. truncatula was described by amplicon mass sequencing and M. truncatula performance was also assessed. The richness and evenness of M. truncatula's root-endophytic fungal community were explained by the small-scale plant neighborhood of the soil samples. For instance, the occurrence of Brachypodium pinnatum in the neighborhood induced higher and lower richness of Sordariomycetes and Glomeromycetes, respectively, whereas Holcus mollis decreased the OTU evenness of the entire mycobiota. These changes in fungal clade OTU richness and evenness were related to modifications in the biomass of M. truncatula. These results indicate that a given plant endophytic fungal community is determined in part by the neighboring plants. Considering that changes in endophytic fungal community are correlated with the plant biomass, this suggests that plant-plant interactions (i.e. competition, facilitation) impacting plant biomass can be mediated by endophytic fungal community changes.
Auteurs, date et publication :
Auteurs Nathan Vannier , Anne-Kristel Bittebiere , Cendrine Mony , Philippe Vandenkoornhuyse
Publication : Fungal Ecology
Date : 2020
Volume : 44
Pages : 100907