Auteurs, date et publication :
Auteurs Juliana Almario , Ganga Jeena , Jörg Wunder , Gregor Langen , Alga Zuccaro , George Coupland , Marcel Bucher
Publication : Proceedings of the National Academy of Sciences
Date : 2017
Volume : 114
Issue : 44
Pages : E9403-E9412
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Across the globe, invasive alien species cause severe environmental changes, altering species composition and ecosystem functions. So far, mountain areas have mostly been spared from large-scale invasions. However, climate change, land-use abandonment, the development of tourism and the increasing ornamental trade will weaken the barriers to invasions in these systems. Understanding how alien species will react and how native communities will influence their success is thus of prime importance in a management perspective. Here, we used a spatially and temporally explicit simulation model to forecast invasion risks in a protected mountain area in the French Alps under future conditions. We combined scenarios of climate change, land-use abandonment and tourism-linked increases in propagule pressure to test if the spread of alien species in the region will increase in the future. We modelled already naturalized alien species and new ornamental plants, accounting for interactions among global change components, and also competition with the native vegetation. Our results show that propagule pressure and climate change will interact to increase overall species richness of both naturalized aliens and new ornamentals, as well as their upper elevational limits and regional range-sizes. Under climate change, woody aliens are predicted to more than double in range-size and herbaceous species to occupy up to 20% of the park area. In contrast, land-use abandonment will open new invasion opportunities for woody aliens, but decrease invasion probability for naturalized and ornamental alien herbs as a consequence of colonization by native trees. This emphasizes the importance of interactions with the native vegetation either for facilitating or potentially for curbing invasions. Overall, our work highlights an additional and previously underestimated threat for the fragile mountain flora of the Alps already facing climate changes, land-use transformations and overexploitation by tourism.
Auteurs, date et publication :
Auteurs Marta Carboni , Maya Guéguen , Ceres Barros , Damien Georges , Isabelle Boulangeat , Rolland Douzet , Stefan Dullinger , Guenther Klonner , Mark van Kleunen , Franz Essl , Oliver Bossdorf , Emily Haeuser , Matthew V. Talluto , Dietmar Moser , Svenja Block , Luisa Conti , Iwona Dullinger , Tamara Münkemüller , Wilfried Thuiller
Publication : Global Change Biology
Date : 2025
Volume : 24
Issue : 1
Pages : e289-e302
Catégorie(s)
#CNRS #Lautaret #UGAAuteurs, date et publication :
Auteurs Thomas Pommier , Amélie A. M. Cantarel , Karl Grigulis , Sandra Lavorel , Nicolas Legay , Catherine Baxendale , Richard D. Bardgett , Michael Bahn , Franck Poly , Jean-Christophe Clément , Marney Isaac
Publication : Journal of Applied Ecology
Date : 2025
Volume : 55
Issue : 1
Pages : 49-58
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Methods: A manipulative experiment tested the reciprocal effects of mowing cessation and mowing resumption for ten years. We analysed floristic composition data following four steps. First, we used the Community Structure Integrity Index (CSII) (Jaunatre et al. 2013) to obtain qualitative and quantitative summaries of taxonomic responses. The second step focused on taxonomic biodiversity using species richness, Simpson and Pielou indices, and on responsive species identified in the first step. Third, we analyzed functional diversity responses using functional groups and community weighted mean (CWM) of vegetative plant traits. Finally, we quantified ecosystem services impacts by estimating fodder quantity and quality using trait-based models.
Results: The mowing manipulation demonstrated the high resilience of P. paniculata grasslands, and revealed reversibility of transitions between mown and unmown states. By reducing the abundance of P. paniculata, the resumption of mowing restored forage quality. Supported by a complementary case study on post-disturbance resowing in hay meadows, this study demonstrates the resilience of mown subalpine grasslands to management change and explores underlying belowground mechanisms of vegetative regeneration and belowground reserves.
Conclusion: Our novel multi-indicator approach provides multi-faceted mechanistic understanding necessary to anticipate impacts of socio-ecological changes and to maintain the multiple benefits of mountain grasslands. Addressing the different facets of biodiversity from abundance data that is systematically collected in impact or monitoring assessment, this approach provides a common framework, widely applicable for different types of restoration or management interventions, across regions and biota.
Auteurs, date et publication :
Auteurs Iris Lochon , Marie-Pascale Colace , Caroline Devaux , Karl Grigulis , Ricarda Rettinger , Sandra Lavorel
Publication : Applied Vegetation Science
Date : 2025
Volume : 21
Issue : 4
Pages : 636-646
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Nitrogen (N) emissions associated with urbanization exacerbate the atmospheric N influx to remote ecosystems – like mountains –, leading to well-documented detrimental effects on ecosystems (e.g., soil acidification, pollution of freshwaters). Here, the importance and fate of N deposition in a watershed was evaluated along a montane to urban gradient, using a multi-isotopic tracers approach (Δ17O, δ15N, δ18O of nitrate, δ2H and δ18O of water). In this setting, the montane streams had higher proportions of atmospheric nitrate compared to urban streams, and exported more atmospheric nitrate on a yearly basis (0.35 vs 0.10 kg-N ha−1 yr−1). In urban areas, nitrate exports were driven by groundwater, whereas in the catchment head nitrate exports were dominated by surface runoff. The main sources of nitrate to the montane streams were microbial nitrification and atmospheric deposition, whereas microbial nitrification and sewage leakage contributed most to urban streams. Based on the measurement of δ15N and δ18O-NO− 3 , biological processes such as denitrification or N assimilation were not predominant in any streams in this study. The observed low δ15N and δ18O range of terrestrial nitrate (i. e., nitrate not coming from atmospheric deposition) in surface water compared to literature suggests that atmospheric deposition may be underestimated as a direct source of N.
Auteurs, date et publication :
Auteurs Ilann Bourgeois , Joel Savarino , Julien Némery , Nicolas Caillon , Sarah Albertin , Franck Delbart , Didier Voisin , Jean-Christophe Clément
Publication : Science of The Total Environment
Date : 2025
Volume : 633
Pages : 329-340
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Nitrogen is an essential nutrient for life on Earth, but in excess, it can lead to environmental issues (e.g., N saturation, loss of biodiversity, acidification of lakes, etc.). Understanding the nitrogen budget (i.e., inputs and outputs) is essential to evaluate the prospective decay of the ecosystem services (e.g., freshwater quality, erosion control, loss of high patrimonial-value plant species, etc.) that subalpine headwater catchments provide, especially as these ecosystems experience high atmospheric nitrogen deposition. Here, we use a multi-isotopic tracer (Δ17O, δ15N and δ18O) of nitrate in aerosols, snow, and streams to assess the fate of atmospherically deposited nitrate in the subalpine watershed of the Lautaret Pass (French Alps). We show that atmospheric N deposition contributes significantly to stream nitrate pool year-round, either by direct inputs (up to 35%) or by in situ nitrification of atmospheric ammonium (up to 35%). Snowmelt in particular leads to high exports of atmospheric nitrate, most likely fast enough to impede assimilation by surrounding ecosystems. Yet, in a context of climate change, with shorter snow seasons, and increasing nitrogen emissions, our results hint at possibly stronger ecological consequences of nitrogen atmospheric deposition in the close future.
Auteurs, date et publication :
Auteurs Ilann Bourgeois , Joël Savarino , Nicolas Caillon , Hélène Angot , Albane Barbero , Franck Delbart , Didier Voisin , Jean-Christophe Clément
Publication : Environmental Science & Technology
Date : 2018
Volume : 52
Issue : 10
Pages : 5561-5570
Catégorie(s)
#CNRS #Lautaret #UGARésumé
The leaf economics spectrum (LES) is based on a suite of leaf traits related to plant functioning and ranges from resource-conservative to resource-acquisitive strategies. However, the relationships with root traits, and the associated belowground plant functioning such as N uptake, including nitrate (NO3−) and ammonium (NH4+), is still poorly known. Additionally, environmental variations occurring both in time and in space could uncouple LES from root traits. We explored, in subalpine grasslands, the relationships between leaf and root morphological traits for three dominant perennial grass species, and to what extent they contribute to the whole-plant economics spectrum. We also investigated the link between this spectrum and NO3− and NH4+ uptake rates, as well as the variations of uptake across four grasslands differing by the land-use history at peak biomass and in autumn. Although poorly correlated with leaf traits, root traits contributed to an economic spectrum at the whole plant level. Higher NH4+ and NO3− uptake abilities were associated with the resource-acquisitive strategy. Nonetheless, NH4+ and NO3−-uptake within species varied between land-uses and with sampling time, suggesting that LES and plant traits are good, but still incomplete, descriptors of plant functioning. Although the NH4+:NO3− uptake ratio was different between plant species in our study, they all showed a preference for NH4+, and particularly the most conservative species. Soil environmental variations between grasslands and sampling times may also drive to some extent the NH4+ and NO3− uptake ability of species. Our results support the current efforts to build a more general framework including above- and below-ground processes when studying plant community functioning.
Auteurs, date et publication :
Auteurs Nicolas Legay , Fabrice Grassein , Cindy Arnoldi , Raphael Segura , Philippe Laîné , Sandra Lavorel , Jean-Christophe Clément
Publication : Oikos
Date : 2025
Volume : 129
Issue : 6
Pages : 830-841
Catégorie(s)
#CNRS #Lautaret #UGARésumé
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
Most models simulating snow albedo assume a flat and smooth surface, neglecting surface roughness. However, the presence of macroscopic roughness leads to a systematic decrease in albedo due to two effects: (1) photons are trapped in concavities (multiple reflection effect) and (2) when the sun is low, the roughness sides facing the sun experience an overall decrease in the local incidence angle relative to a smooth surface, promoting higher absorption, whilst the other sides have weak contributions because of the increased incidence angle or because they are shadowed (called the effective-angle effect here). This paper aims to quantify the impact of surface roughness on albedo and to assess the respective role of these two effects, with (1) observations over varying amounts of surface roughness and (2) simulations using the new rough surface ray-tracing (RSRT) model, based on a Monte Carlo method for photon transport calculation. The observations include spectral albedo (400-1050 nm) over manually created roughness surfaces with multiple geometrical characteristics. Measurements highlight that even a low fraction of surface roughness features (7% of the surface) causes an albedo decrease of 0.02 at 1000 nm when the solar zenith angle (theta(s)) is larger than 50 degrees. For higher fractions (13 %, 27% and 63 %), and when the roughness orientation is perpendicular to the sun, the decrease is of 0.03-0.04 at 700 nm and of 0.06-0.10 at 1000 nm. The impact is 20% lower when roughness orientation is parallel to the sun. The observations are subsequently compared to RSRT simulations. Accounting for surface roughness improves the model observation agreement by a factor of 2 at 700 and 1000 nm (errors of 0.03 and 0.04, respectively) compared to simulations considering a flat smooth surface. The model is used to explore the albedo sensitivity to surface roughness with varying snow properties and illumination conditions. Both multiple reflections and the effective-angle effect have a greater impact with low specific surface area (SSA; < 10m(2) kg(-1)). The effective-angle effect also increases rapidly with theta(s) at large theta(s). This latter effect is larger when the overall slope of the surface is facing away from the sun and has a roughness orientation perpendicular to the sun. For a snowpack where artificial surface roughness features were created, we showed that a broadband albedo decrease of 0.05 may cause an increase in the net shortwave radiation of 80% (from 15 to 27Wm(-2)). This paper highlights the necessity of considering surface roughness in the estimation of the surface energy budget and opens the way for considering natural rough surfaces in snow modelling.
Auteurs, date et publication :
Auteurs Fanny Larue , Ghislain Picard , Laurent Arnaud , Ines Ollivier , Clement Delcourt , Maxim Lamare , Francois Tuzet , Jesus Revuelto , Marie Dumont
Publication : CRYOSPHERE
Date : 2020
Volume : 14
Issue : 5
Pages : 1651-1672