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Apport de la télédétection satellitaire optique/thermique haute résolution à la prédiction de la sévérité des incendies de forêt en zone méditerranéenne française
No full textClimate change is a major threat to Mediterranean forest ecosystems, particularly due to the increased risk of wildfires. However, the impact of fires on the environment, ie fire severity, remains poorly studied in the French Mediterranean region. Although the variability factors are well known (meteorological and fuel conditions, topography), the models predicting potential fire severity, that are mainly developed in the United States, are difficult to generalize. The assumption is that the predictors currently used are incomplete and/or too uncertain at the spatial scales considered. In this context of predicting potential fire severity in the Mediterranean region, this thesis aims to 1) test new predictors, and 2) develop new indicators of ecosystem hydric stress using high-resolution thermal infrared satellite data. The first part of the thesis focuses on the use of pre-fire temporal dynamics of fuel state proxies in fire severity prediction models. Pre-fire time series of a vegetation index derived from remote sensing (Sentinel-2, Landsat-7/8) and drought indices derived from meteorological data are extracted from 79 summer fires (2016-2021). Considering fuel dynamics during the 2 months preceding the fire improves prediction performance by 32% compared to the benchmark model that only uses data measured or computed just before the fire. Faster-than-average increases in drought and faster-than-average decreases in live fuel quantity favour higher-than-average severities. The second part of the thesis focuses on estimating hydric stress in Mediterranean forests using optical/thermal data (Landsat-7/8/9) and high-definition LIDAR data from IGN. The contextual method, commonly applied to relatively low and homogeneous land covers, is originally adapted to the case of forests. The results are evaluated on two Mediterranean forest sites where eddy-covariance system measurements are available for 9 years. Surface roughness (function of canopy height) and directional effects (tree casting shadows) are identified as variability factors of Landsat surface temperature (LST), independently of hydric stress. A method for normalizing LST for canopy height effects and correcting for cast shadows is developed. This method reduces bias in satellite estimates and significantly increases their sensitivity to in situ measured hydric stress compared to the method without normalization and correction. Hydric stress derived from thermal data could be used as a predictor of potential fire severity.Le changement climatique est une menace majeure pour les écosystèmes forestiers méditerranéens, en particulier du fait de l'augmentation du risque incendie. Pourtant, l'impact des incendies sur le milieu, ie la sévérité d'un incendie, reste encore peu étudié en région méditerranéenne française. Bien que les facteurs de variabilité soient bien connus (conditions météorologiques, état du combustible, topographie), les modèles de prédiction de la sévérité potentielle, principalement développés aux États-Unis, sont difficilement généralisables. L'hypothèse est que les prédicteurs utilisés actuellement sont incomplets et/ou trop incertains aux échelles spatiales considérées. Dans ce contexte de prévision de la sévérité potentielle des incendies en région méditerranéenne, cette thèse a pour objectif de 1) tester de nouveaux prédicteurs, et 2) développer de nouveaux indicateurs du stress hydrique des écosystèmes à partir des données satellitaires infrarouges thermiques à haute résolution spatiale. La première partie de la thèse s'intéresse à la prise en compte des dynamiques temporelles pré-feu de proxys de l'état du combustible dans les modèles de prédiction de la sévérité. Les séries temporelles pré-feu d'un indice de végétation issu de la télédétection (Sentinel-2, Landsat-7/8) et d'indices de sécheresse dérivés des données météorologiques sont extraites de 79 incendies estivaux (2016-2021). La prise en compte des dynamiques du combustible durant les 2 mois précédant l'incendie améliore la performance de prédiction de 32% par rapport au modèle de référence qui n'utilise que les données juste avant l'incendie. Une augmentation plus rapide que la moyenne de la sécheresse et une diminution plus rapide que la moyenne de la quantité de combustible vivant favorisent des sévérités plus élevées que la moyenne. La deuxième partie de la thèse s'intéresse à l'estimation du stress hydrique des forêts méditerranéennes à partir des données optiques/thermiques (Landsat-7/8/9) et des données LIDAR haute définition de l'IGN. La méthode contextuelle, couramment appliquée aux couverts relativement bas et de structure homogène, est adaptée de manière originale au cas des forêts. Les résultats sont évalués sur deux sites forestiers méditerranéens où des mesures par système eddy-covariance sont disponibles pendant 9 ans. La rugosité de surface (fonction de la hauteur de canopée) et les effets directionnels (ombres portées des arbres) sont identifiés comme des facteurs de variabilité de la température de surface (LST) Landsat, indépendamment du stress hydrique. Une méthode de normalisation de la LST des effets de hauteur de canopée et une correction de l'effet des ombres portées sont donc développées. Elles permettent de réduire le biais sur les estimations satellitaires et d'augmenter leur sensibilité au stress hydrique mesuré in situ de manière très significative par rapport à la méthode sans normalisation ni correction. Le stress hydrique dérivé des données thermiques pourrait être utilisé comme prédicteur de la sévérité potentielle
Portfolio 1 : Hevea brasiliensis à Vila Franca: Circulations bioculturelles et mise en marché d’une Amazonie recomposée
No full textInternational audienc
Spider Webs, Soil or Leaf Swabs to Detect Environmental DNA From Terrestrial Vertebrates: What Is the Best Substrate?
No full textData Availability Statement: Genetic data: Raw sequence reads are deposited in Zenodo (https://doi.org/10.5281/zenodo.14843633), Sample metadata: Related metadata can also be found in Zenodo (https://doi.org/10.5281/zenodo.14843633) (including: (a) a metadata file describing the FASTQ files, (b) a metadata file with georeferenced data, (c) raw and filtered abundance tables, and (d) the R script required to reproduce the analyses).International audienceAs human activities drive biodiversity decline, effective biomonitoring is more crucial than ever to track species distribution changes and inform conservation and restoration actions. Environmental DNA (eDNA) metabarcoding has emerged as a promising tool for the simultaneous detection of multiple taxa. However, while substrates play a crucial role in eDNA studies, limited research has compared substrate performance for terrestrial vertebrate detection, leaving a critical gap in empirical knowledge for large-scale application. This study evaluates and compares the effectiveness of three easy-to-collect substrates: soil, leaf swabs, and spider webs, for broad terrestrial vertebrate eDNA monitoring. Specifically, we examined taxonomic richness overlaps among substrates, their effects on wild vertebrate detection probabilities, and within-sample PCR repeatability. We analysed 120 samples from the Landes Forest, an intensively managed temperate forest in Western France, and included additional control samples from the Montpellier zoo to validate our detection capabilities. Using metabarcoding with 12S-V5 and 16S mam primers, we identified 63 taxa at the genus or species level. Our findings highlight the advantages of substrates that passively accumulate airborne DNA (leaf swabs and spider webs) over soil, and position spider webs as a suitable choice for maximising detection probabilities in rapid eDNA surveys, emphasising their potential for efficient, scalable biomonitoring. Further research is needed to identify factors affecting eDNA detectability from these substrates, aiming to standardise procedures and move from proof-of-concept to broad use by researchers and managers
A tool for economists to make the search for conferences and special issues more efficient and transparent
No full textEach year, hundreds of economics conferences, workshops, and seminars take place around the world. For researchers, timely access to clear information-especially regarding calls for papers and special issues-is essential to target the right venues and improve their chances of publication. Organizers also benefit from reaching the right contributors to maintain the quality and relevance of their events. ConfWatcher is a tool designed specifically for economists to meet this need. It combines web scraping, text analysis and generative artificial intelligence via large language models (LLMs) to automatically identify and monitor relevant academic events. The platform focuses on high-quality conferences organized by central banks, international organizations, journals, research centers, and professional associations. With its simple and userfriendly interface, ConfWatcher helps economists stay informed, plan submissions more strategically, and connect with the most valuable opportunities in their field.</div
Ant–plant relationships in an Amazonian rainforest understory: A network approach
No full textInternational audience1. Although tropical rainforest ants are abundant and have high species richness, with their community structure well known at the canopy and ground levels, the understory is frequently neglected. 2. To fill this gap, we looked for ants nesting in this stratum in an Amazonian rainforest and noted the occurrence of colonies in the debris accumulated between the fronds of the palm tree Astrocaryum sciophilum or associated with eight myrmecophytes (i.e., plants that shelter ant colonies in hollow structures called domatia).3. We analysed these plant-ant relationships by conducting a network approach looking for the degree of specialisation between partners (specialisation index), the differences in intensity between links (weighted nestedness) and the proportion of realised interactions relative to the number of potential interactions (connectance), including ground-and canopy-nesting ants.4. This results in a highly modular pattern of interactions with one module per plant species based on the 98 ant species recorded. We showed the importance of ground-nesting species for Astrocaryum, although 40.5% of them sheltered a colony of the arboreal Odontomachus hastatus. Among myrmecophytes, a strong specificity was noted for Hirtella physophora (Chrysobalanaceae) and Maieta guianensis (Melastomataceae) that sheltered at more than 90% Allomerus decemarticulatus and Pheidole minutula, respectively. Cordia nodosa (Boraginaceae) has an intermediary value (45.3% associated with Allomerus octoarticulatus), whereas Cecropia obtusa (Urticaceae), Duroia longiflora (Rubiaceae), Tachigali paniculata (Fabaceae) and Tococa guianensis (Melastomataceae) can shelter several ant species belonging mostly to a single genus. Tachia guianensis, considered a 'non-specialised' myrmecophyte, shelters species from different genera.</p
Les effets de la tarification carbone et des financements climatiques sur l'économie Malagasy: application à travers un modèle DSGE
No full textInternational audienceHaving become a central global concern, the large-scale spread of greenhouse gas emissions into the atmosphere generates undesirable effects both on the environment and on the economic system. The severity of the consequences of climate change has, however, reshaped economic challenges and strategies. Major reorientations of economic policies—particularly climate policies—based mainly on the level of CO2 emissions have been adopted during the various Conferences of the Parties (COP).This issue has thus led us to investigate the effects of these climate policies on the overall economy. To achieve our objective, a climate DSGE model reflecting the characteristics of Madagascar was implemented. The results of the impulse response analysis revealed that dynamic carbon taxation proves to be more effective in reducing CO2 emissions compared to a quota policy, which tends to be a source of volatility. As for climate finance, it is insufficient to stimulate the economy if not combined with carbon pricing.Devenue une préoccupation centrale à l'échelle planétaire, la propagation en quantité importante des émissions de gaz à effet de serre dans l'atmosphère cause des effets non désirables tant au niveau environnemental que sur le système économique. La sévérité des conséquences du dérèglement climatique a cependant bouleversée les enjeux et les stratégies économiques. Des réorientations majeures de politiques économiques, en particulier des politiques climatiques, fondées surtout sur le niveau d'émissions de CO 2 ont été prises au cours des différentes Conférences des Parties (COP). Cette problématique nous a ainsi conduit à effectuer des investigations sur les effets de ces politiques climatiques sur l'ensemble de l'économie. Pour atteindre notre objectif, un modèle DSGE climatique qui revêt les caractéristiques de Madagascar a été implémenté. Les résultats des réponses impulsionnelles ont révélé que la taxation dynamique sur le carbone se voit plus efficace à réduire les émissions de CO 2 en comparaison à la politique de quotas qui est une source de volatilité. Les finances climatiques, quant à elles, sont insuffisantes pour stimuler l'économie si elles ne sont pas combinées avec une tarification carbone
Phytoremède et innovation : le CNS-Sinusite, un exemple ivoirien
No full textInternational audienceBased on the biography of an Ivorian phytoremedy, this text not only reflects on the relevance of pharmaceuticalization as an analytical concept, but also rethinks the articulation between the governance of traditional medicine and the therapeutic knowledge at the origin of a hybrid therapeutic practice born in a singular political and institutional context. It aims to contribute to theoretical and epistemological debates concerning the pharmaceuticalization of African societies, by questioning its contemporary urban specificities.Partant de la biographie d'un phytoremède ivoirien, ce texte permet non seulement de réfléchir à la pertinence de la pharmaceuticalisation comme concept analytique, mais aussi de repenser l'articulation entre gouvernance de la médecine traditionnelle et savoirs thérapeutiques à l'origine d'une pratique thérapeutique hybride née dans un contexte politique et institutionnel singuliers. Il vise à contribuer aux débats théoriques et épistémologiques concernant la pharmaceuticalisation des sociétés africaines, en interrogeant ses spécificités urbaines contemporaines
AquaEcOmics meeting: exploring aquatic ecology through omics. March 17-20, 2025. Program and abstracts booklet
No full textA meeting to explore aquatic ecosystems biodiversity, functionning and monitoring with eDNA and multi-Omics method
Continuous monitoring of fire-induced forest loss using Sentinel-1 SAR Time Series and a Bayesian method: A case study in Paragominas, Brazil
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/614390/)International audienceForest fires, intensified by climate change, threaten tropical ecosystems by accelerating biodiversity loss, releasing carbon emissions, and altering hydrological cycles. Continuous detection of fire-induced forest loss is therefore critical. However, commonly used optical- based methods often face limitations, particularly due to cloud cover and coarse spatial resolution. This study explores the use of C-band Sentinel-1 Synthetic Aperture Radar (SAR) time series, combined with Bayesian Online Changepoint Detection (BOCD), for detecting and continuously monitoring fire-induced vegetation loss in forested areas. Three BOCD variants are evaluated: two single-polarization approaches individually using VV and VH reflectivities, and a dual-polarization approach (pol-BOCD) integrating both channels. The analysis focuses on a fire-affected area in Baixo Uraim (Paragominas, Brazil), supported by field-validated reference data. BOCD performance is compared against widely used optical products, including MODIS and VIIRS active fire and burned area data, as well as Sentinel-2-based difference Normalized Burn Ratio (dNBR) assessments. Results indicate that pol-BOCD achieves spatial accuracy comparable to dNBR (88.2% agreement), while enabling detections within a delay of three Sentinel-1 acquisitions. These findings highlight the potential of SAR-based BOCD for rapid, cloud-independent monitoring. While SAR enables continuous detection regardless of atmospheric conditions, optical imagery remains essential for characterizing the type and severity of change