Résumé
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
Catégorie(s)
#ANR-Citation #CNRS #Lautaret #UGARésumé
Urban habitat characteristics create environmental filtering of pollinator communities. They also impact pollinating insect phenology through the presence of an urban heat island and the year-round availability of floral resources provided by ornamental plants. Here, we monitored the phenology and composition of pollinating insect communities visiting replicates of an experimental plant assemblage comprising two species, with contrasting floral traits:Sinapis albaandLotus corniculatus, whose flowering periods were artificially extended. Plant assemblage replicates were set up over two consecutive years in two different habitats: rural and densely urbanized, within the same biogeographical region (Ile-de-France region, France). The phenology of pollination activity, recorded from the beginning (early March) to the end (early November) of the season, differed between these two habitats. Several pollinator morphogroups (small wild bees, bumblebees, honeybees) were significantly more active on our plant sets in the urban habitat compared to the rural one, especially in early spring and autumn. This resulted in different overall reproductive success of the plant assemblage between the two habitats. Over the course of the season, reproductive success ofS. albawas always significantly higher in the urban habitat, while reproductive success ofL. corniculatuswas significantly higher in the urban habitat only during early flowering. These findings suggest different phenological adaptations to the urban habitat for different groups of pollinators. Overall, results indicate that the broadened activity period of pollinating insects recorded in the urban environment could enhance the pollination function and the reproductive success of plant communities in cities.
Auteurs, date et publication :
Auteurs Vincent Zaninotto , Xavier Raynaud , Emmanuel Gendreau , Yvan Kraepiel , Eric Motard , Olivier Babiar , Amandine Hansart , Cecile Hignard , Isabelle Dajoz
Publication : ECOLOGY AND EVOLUTION
Date : 2020
Volume : 10
Issue : 20
Pages : 11607-11621
Catégorie(s)
#ANR-Citation #CEREEP #CNRS #ENSRésumé
Asexual reproduction has often been regarded as an evolutionary dead end, but asexual lineages (most notably those that are apomictic) are present in several angiosperm families and often comprise a large number of taxa, both widespread and endemic. Investigating correlations between genetic, environmental and taxonomic factors and the incidence of apomixis has represented a challenge for many years, with previous analyses frequently omitting one or more of these variables. Here, flow cytometric seed screening, cytological data and ecological variables have been integrated in a phylogenetic framework to create a comprehensive dataset for 229 of Asteraceae from the European Alps. Data were analysed using phylogenetically informed generalized linear mixed models (pMCMCglmm) where elevation, ploidy and phenology were assessed for their potential correlation with asexual reproduction and apomixis type. Although apomixis is not dominant among the species studied, our results confirm that an odd ploidy (e.g. 3x) and, to a lesser extent, an even polyploid level (i.e. 4x) significantly increase its probability, most probably due to chromosome misalignments during meiosis. The distribution of apomictic species does not correlate with elevation, and there is a weak correlation between early flowering initiation and aposporous apomixis. Although current and future changes in climate may severely impact the survival of the flora of the European Alps, asexual reproduction and polyploidization may prove to be, at least temporarily, lifelines for the survival of a species under the novel climatic conditions. Therefore, uncovering how apomicts and polyploids evolve and persist will be essential for understanding the ecology of the European Alps and hence informing future conservation strategies.
Auteurs, date et publication :
Auteurs Luca Pegoraro , Ellen C Baker , David Aeschimann , Manica Balant , Rolland Douzet , Teresa Garnatje , Maïté S Guignard , Ilia J Leitch , Andrew R Leitch , Luis Palazzesi , Jean-Paul Theurillat , Oriane Hidalgo , Jaume Pellicer
Publication : Botanical Journal of the Linnean Society
Date : 2020
Volume : 194
Issue : 4
Pages : 410-422
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Egg size has a crucial impact on the reproductive success of a mother and the performance of her offspring. It is therefore reasonable to employ egg size as a proxy for egg content when studying variation in offspring performance. Here, we tested species differences in allometries of several egg content parameters with egg area. We measured individual eggs in five species of annual killifish (Cyprinodontiformes), a group of fish where egg banks permit population survival over dry season. Apart from comparing allometric scaling exponents, amounts and compositions of egg components across the different species, we assessed the explanatory power of egg area for egg wet and dry weight and for hatchling size. We found notable species-specific allometries between egg area and the other egg parameters (egg dry weight and water content, elemental composition and triglyceride content). Across species, egg area predicted egg wet weight with highest power. Within species, coefficients of determination were largest in A. elongatus, a large piscivorous species with large eggs. Our study shows that systematically using egg area as a proxy of egg content between different species can ignore relevant speciesspecific differences and mask within-species variability in egg content.
Auteurs, date et publication :
Auteurs Milan Vrtilek , Tom J. M. Van Dooren , Megane Beaudard
Publication : COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY
Date : 2020
Volume : 249
Catégorie(s)
#ANR-Citation #CEREEP #CNRS #ENSRésumé
A major challenge remains to understand the relative contributions of history, dispersal, and environmental filtering to the assembly of hyperdiverse communities across spatial scales. Here, we examine the extent to which biogeographical history and habitat specialization have generated turnover among and within lineages of Amazonian trees across broad geographic and environmental gradients. We replicated standardized tree inventories in 102 0.1-ha plots located in two distant regions—the western Amazon and the eastern Guiana shield. Within each region, we used a nested design to replicate plots on contrasted habitats: white-sand, terra firme, and seasonally flooded forests. Our plot network encompassed 26,386 trees that together represented 2,745 distinct taxa, which we standardized across all plots and regions. We combined taxonomic and phylogenetic data with detailed soil measurements and climatic data to: (1) test whether patterns of taxonomic and phylogenetic composition are consistent with recent or historical processes, (2) disentangle the relative effects of habitat, environment, and geographic distance on taxonomic and phylogenetic turnover among plots, and (3) contrast the proportion of habitat specialists among species from each region. We found substantial species turnover between Peru and French Guiana, with only 8.8% of species shared across regions; genus composition remained differentiated across habitats and regions, whereas turnover at higher taxonomic levels (family, order) was much lower. Species turnover across plots was explained primarily by regions, but also substantially by habitat differences and to a lesser extent by spatial distance within regions. Conversely, the composition of higher taxonomic levels was better explained by habitats (especially comparing white-sand forests to other habitats) than spatial distance. White-sand forests harbored most of the habitat specialists in both regions, with stronger habitat specialization in Peru than in French Guiana. Our results suggest that recent diversification events have resulted in extremely high turnover in species and genus composition with relatively little change in the composition of higher lineages. Our results also emphasize the contributions of rare habitats, such as white-sand forests, to the extraordinary diversity of the Amazon and underline their importance as conservation priorities.
Auteurs, date et publication :
Auteurs Christopher Baraloto , Jason Vleminckx , Julien Engel , Pascal Petronelli , Nállarett Dávila , Marcos RÍos , Elvis Harry Valderrama Sandoval , Italo Mesones , Juan Ernesto Guevara Andino , Claire Fortunel , Elodie Allie , C. E. Timothy Paine , Aurélie Dourdain , Jean-Yves Goret , Oscar J. Valverde-Barrantes , Freddie Draper , Paul V. A. Fine
Publication : Ecological Monographs
Date : 2025
Volume : 91
Issue : 4
Pages : e01473
Catégorie(s)
#CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Shirley J Serrano-Rojas , Andrius Pašukonis
Publication : Journal of Experimental Biology
Date : 2025
Volume : 224
Issue : 21
Pages : jeb243122
Catégorie(s)
#ANR-Citation #CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Marie-Eugénie Maggia , Thibaud Decaëns , Emmanuel Lapied , Lise Dupont , Virginie Roy , Heidy Schimann , Jérôme Orivel , Jérôme Murienne , Christopher Baraloto , Karl Cottenie
Publication : Applied Soil Ecology
Date : 2025
Volume : 164
Pages : 103932
Catégorie(s)
#CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Hervé Lormée , Rachel Berzins , Vincent Rocheteau , Fran De Coster , Thomas Denis , Cécile Richard-Hansen
Publication : Tropical Conservation Science
Date : 2025
Volume : 14
Pages : 19400829211026170
Catégorie(s)
#CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Lynsay Spafford , Guerric Le Maire , Andrew MacDougall , Florian De Boissieu , Jean-Baptiste Feret
Publication : Remote Sensing of Environment
Date : 2025
Volume : 252
Pages : 112176
Catégorie(s)
#ANR-Citation #CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Céline Leroy , Arthur QuyManh Maes , Eliane Louisanna , Heidy Schimann , Nathalie Séjalon‐Delmas
Publication : New Phytologist
Date : 2025