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In Europe, ticks are the primary vectors of pathogens for both humans and animals, and thus represent a serious issue in terms of public and veterinary health. Ixodes ricinus, the predominant tick species in Western Europe, is known to transmit the largest variety of pathogens, including Borrelia burgdorferi s.l., the Lyme disease agent. In addition to pathogens, ticks also carry a multitude of other microorganisms, which can influence the acquisition and / or transmission of pathogens, and thus affect the tick vector competence. This information led to take into account the concept of pathobiome, which aims to consider the pathogen in its biotic environment, including other microorganisms hosted by ticks. Moreover, these microbial communities constitute dynamic systems whose composition and diversity are likely to vary at different scales. On one hand at the scale of the tick, according to the tick species, the individual, the stage, or organs, and on the other hand at the temporal or spatial scale. In this context, the understanding of the different factors that can influence the vector competence of ticks, requires to consider first the notion of pathobiome, but also, the scale concept and the dynamic aspect of this system. In this context, my research project aimed to characterize the dynamics of the I. ricinus pathobiome. For this purpose, two scales were considered: the temporal scale and the tick organs. The first part of my thesis consisted to identify the dynamics of pathogens, on one hand, in ticks collected monthly for three consecutive years, and on the other hand, in two key organs: the digestive tract and salivary glands. We used a high-throughput screening technique, the microfluidic PCR. At the organ scale, the results led us to put into perspective previous postulates regarding the transmission mechanisms of certain pathogens, and more particularly the Borrelia. At the temporal scale, we characterized the dynamics of several pathogenic species belonging to the genera, Borrelia, Anaplasma, Rickettsia and Babesia, well known to circulate in I. ricinus ticks in the studied area. We also highlighted significant differences in prevalence for several of these pathogens depending on the season or years. Then, the microbiota of ticks collected for the temporal study was characterized by high-throughput sequencing of the 16S RNA gene. We also tried to identify potential interactions between the different members of these microbial communities using network analysis. After an in depth methodological development to remove potential contaminations, we showed that tick microbiota is highly dominated by several bacterial genera corresponding to common maternally inherited bacteria in different arthropod species (Arsenophonus, Candidatus Midichloria, Rickettsia, Wolbachia and Spiroplasma). This study also allowed us to observe an effect according to the season at which the ticks were sampled, which appeared to be mainly due to microorganisms commonly found in the environment. Finally, we identified a large number of links between members of the microbiota, some of which involving several taxa of the Rickettsia genus, potentially pathogenic. All our results confirm that the pathobiome of ticks is a dynamic system, which must be studied at different scales., En Europe, les tiques représentent les premiers vecteurs d’agents pathogènes pour l’homme et l’animal, et constituent ainsi un problème de santé publique et vétérinaire préoccupant. Ixodes ricinus, espèce de tique prédominante en Europe occidentale, est l’espèce capable de transmettre la plus grande variété d’agents pathogènes, dont les bactéries du complexe Borrelia burgdorferi s.l., agents de la maladie de Lyme. Outre les agents pathogènes, les tiques sont également porteuses d’une multitude d’autres micro-organismes, capables d’influencer l’acquisition et/ou la transmission des agents pathogènes. Ces informations ont ainsi conduit à prendre en compte le concept de pathobiome, qui vise à considérer les interactions entre l’agent pathogène et son environnement biotique, notamment les autres micro-organismes hébergés par les tiques. Par ailleurs, ces communautés microbiennes constituent des systèmes dynamiques dont la composition et la diversité sont susceptibles de varier, d’une part à l’échelle de la tique et d’autre part à l’échelle temporelle ou spatiale. Ainsi la compréhension des différents facteurs pouvant influer sur la compétence vectorielle des tiques, nécessite, non seulement, de considérer la notion de pathobiome dans l’étude des tiques et des agents pathogènes qu’elles transmettent, mais aussi, de bien considérer cette notion d’échelle et l’aspect dynamique de ce système. Dans un tel contexte, mon projet de thèse visait à caractériser la dynamique du pathobiome de tiques I. ricinus. Pour cela deux échelles ont été considérées : l’échelle temporelle et les organes des tiques. La première partie de ma thèse consistait à identifier la dynamique des agents pathogènes d’une part dans des tiques collectées mensuellement pendant trois années consécutives et d’autre part dans deux organes clés : le tube digestif et les glandes salivaires. Pour cela, nous avons utilisé une technique de criblage haut-débit, la PCR microfluidique. À l’échelle des organes, les résultats obtenus nous ont conduit à remettre en perspective certains postulats établis quant aux mécanismes de transmission de certains agents pathogènes, et plus particulièrement les Borrelia. À l’échelle temporelle, nous avons pu caractériser la dynamique de plusieurs espèces pathogènes appartenant aux genres, Borrelia, Anaplasma, Rickettsia et Babesia, bien connues pour circuler chez les tiques I. ricinus dans la zone étudiée. Nous avons aussi pu mettre en évidence, des différences de prévalences pour plusieurs de ces agents pathogènes en fonction des saisons ou encore des années d’échantillonnage. Par ailleurs, le microbiote des tiques de l’étude temporelle, a été caractérisé par séquençage haut débit du gène de l’ARN 16s et d’éventuelles interactions entre les différents membres de ces communautés microbiennes ont été recherchées à l’aide d’analyses de réseaux. Après une rigoureuse mise au point méthodologique pour s’affranchir des potentielles contaminations liées aux étapes d’extraction et d’amplification de l’ADN, nous avons montré que le microbiote des tiques était largement dominé par plusieurs genres bactériens correspondant à des bactéries communément transmises verticalement chez différentes espèces d’arthropodes (Arsenophonus, Candidatus Midichloria, Rickettsia, Wolbachia et Spiroplasma). L’étude de l’ensemble du microbiote nous a également permis d’observer un effet de la saison à laquelle les tiques avaient été échantillonnées, qui semblait être principalement le fait de micro-organismes communément retrouvés dans l’environnement. Enfin, nous avons identifié un grand nombre de liens entre les membres du microbiote, dont certains impliquant plusieurs taxons du genre Rickettsia, potentiellement pathogènes. Ainsi, l’ensemble des résultats obtenus au cours de cette thèse, a permis de montrer que le pathobiome des tiques est un système dynamique, qu’il est nécessaire d’étudier à différentes échelles, pour en caractériser le fonctionnement.

Cet article donne un aperçu actuel des données et des méthodes de recherche en climatologie tropicale. Les données météorologiques s’appliquent à la climatologie “actuelle”. Les données utilisées pour l’étude des paléoenvironnements sont d’une autre nature. Dans la zone intertropicale, les données les plus importantes sont les données pluviométriques et les données radiatives (fournies par les radiomètres infrarouges des satellites météorologiques géostationnaires). Les régimes pluviométriques, la nébulosité (convective), sont liés à des échelles spatiales différentes. Ensuite est abordé le problème de la variabilité climatique, spécialement dans l’optique “actualiste”, rendue nécessaire par les besoins économiques à court terme dans de nombreux pays tropicaux (Sahel). Les apports récents de la climatologie dynamique satellitaire et de la climatologie “diagnostique” sont discutés. This paper is an updated view on data and methods in tropical climatology. First, the difference must he made between meteorological data (for present climatology) and proxy data (for palaeoenvironments). In the Tropics, the most important data are rainfall data and energy data (from satellite infrared radiometers). Rainfall rhythms, (convective) cloud patterns are influenced by different spatial scales. Second, climatic variability is shown, in the long term and in the short term. Rural poverty in numerous tropical countries (Sahel) needs precise seasonal weather forecast. But weather and climate are not the same. Results of satellite methods and "diagnostic" global climatology and modelling are discussed.

The focus of this paper is to investigate the ability to assess the flow exchanges between the matrix and the conduits in two karstified watersheds (Aliou and Baget, Ari&egrave, ge, France) using the KarstMod modeling platform. The modeling is applied using hourly and daily time series. First, the flow dynamics between the conduit and the surrounding matrix are described on a rainfall event scale (i.e., a few days). The model allows us to describe a physical reality concerning the flow reversal between matrix and conduit when there is a significant rainfall event. Then, the long-term trends (i.e., inter-annual) in the matrix water level are evidenced using the moving average over shifting horizon method (MASH). The mean water level in the matrix dropped about 10% to 15% since the late 1960s. Also, the matrix recharge has been delayed from February in the late 1960s to April since the 1990s. Moreover, the contribution of the matrix in the total spring flow is estimated though mass balance. It is estimated that the annual matrix contribution in the total spring flow is about 3% and it can increase to up to 25% during periods with low rainfall.

National audience; Lorsque le biogéographe s’intéresse aux paysages actuels, il se pose la question du choix de l’échelle, spatiale mais aussi temporelle. « Question d’échelle : Temps et espace » est ainsi un sujet central dans l’approche méthodologique des paysages conduite par ce chercheur. Dans cette proposition, nous envisageons de confronter cette question aux paysages offerts par un territoire particulier, le Domaine National de Chambord – nous y avons mené des recherches dans le cadre d’un projet interrogeant le rôle des ongulés sauvages dans la formation des paysages, les écosystèmes et les services culturels rendus par ces derniers . La spécificité de ce site d’étude tient au fait qu’il s’agit d’un domaine emmuré – le plus vaste d’Europe. Comme son château, qui est internationalement reconnu, le domaine est chargé d’histoire ; y mener une analyse en vue d’identifier les évolutions spatio-temporelles de ses paysages s’impose d’autant plus pour mieux comprendre leurs caractéristiques actuelles. Mais quelles échelles spatiale(s) et temporelle(s) considérer ? Le projet dans lequel ces recherches ont été conduites dressait comme cadre temporel la période de 1950 à aujourd’hui et comme cadre spatial l’enceinte du parc. Plusieurs questions se sont toutefois bien vite posées pour l’analyse des paysages : peut-on se contenter du territoire délimité par les murs ? Ne faut-il pas le resituer aussi dans son environnement ? De la même manière, peut-on se contenter de la période récente, depuis 1950 ? N’a-t-on pas intérêt à questionner les dynamiques plus anciennes et à prendre ainsi davantage en compte le poids de l’histoire ? Nous avons pris le parti d’étendre spatialement et temporellement l’étude et de faire ainsi varier les échelles, entre le cadre et le contexte. Mais encore s’agissait-il de disposer de sources fiables et pertinentes pour connaître les paysages à des dates clés. Le Domaine national de Chambord est bien documenté ; les sources sont nombreuses. Comme l’objectif était d’identifier les dynamiques spatio-temporelles des paysages, nous avons décidé de nous focaliser sur les sources spatiales (cartes, plans, photographies aériennes et bases de données vectorielles), en vue de les confronter dans un SIG. Il ressort ainsi de notre étude que le Domaine National de Chambord n’a pas toujours été un vaste domaine forestier : de sa création au XVIe siècle jusqu’au XIXe siècle, il incluait, outre la forêt, des landes et des terres agricoles. Par ailleurs, bien qu’emmuré, il apparaît représentatif de l’environnement solognot dans lequel il s’inscrit : les similitudes sont grandes, autant dans les paysages actuels que dans les dynamiques récentes et anciennes. La variation des échelles temporelles et spatiales nous permet ainsi de mieux comprendre les paysages actuels et par là même les caractéristiques (sols, espèces végétales) des sylvosystèmes qui les composent, avec dès lors un intérêt pour les chercheurs des autres disciplines impliqués dans le projet.

La question de la multiplicité des échelles, souvent pointée comme un aspect important de la compréhension et la prévention des risques, reste dans les faits insuffisamment prise en compte. La focalisation sur l’aléa et ses impacts a longtemps fait penser et agir à l’échelle de l’enjeu menacé, sans que l’on n’envisage réellement la dimension spatiale et la temporalité des risques et des catastrophes. L’introduction de la vulnérabilité a permis progressivement d’adopter des approches multiscalaires, qu’il s’agisse d’espace ou de temps. La transformation de certaines menaces en risques globaux et systémiques appelle cependant de nouvelles grilles de lectures certes multi-scalaires mais aussi transcalaires qui permettent de mieux saisir la spatialité et les temporalités de ces menaces et des crises qui en découlent. Hazard and risk studies rarely consider the issue of scale. A focus on physical events and impact approach leads to the conception and management of damaging processes on the scale of elements at risk. Academic works struggle to integrate the spatiality and temporality of risk and crisis. This paper argues that drawing upon the notion of vulnerability allows for a multiscalar and, hence, more thorough, approach in terms of space and time. However, this approach is also challenged by the globalization of certain threats. The transformation of these threats into global and systemic risks calls for a new conceptual framework. Thus, this paper intends to give due consideration to the spatialities and temporalities of “global risk” in order to consider vulnerability both from a cross-scale and a transcalar perspective.

11 páginas.- Ilustraciones.- © 2017 The Authors. Journal of Ecology ©2017 British Ecological Society., 1. Atmospheric nitrogen (N) deposition and climate warming are two major components of global change that drive species richness and composition in plant communities. However, their combined effects have been insufficiently investigated across large spatial and temporal scales particularly in high-elevation, nutrient-limited ecosystems. 2. We examine whether and how N deposition and climate warming have altered the plant richness and the composition of subalpine semi-natural, extensively grazed grasslands of the Pyrenees, using two complementary approaches: (i) analysis of 553 releves to explore vegetation changes across large ecological gradients including temperature and N deposition (spatial approach) and (ii) a re-sampling of a subset of 40 sites among the 553 sites to assess temporal changes over the past decades (temporal approach). 3. Both approaches showed that the vascular plant species richness increased when temperature and cumulative N deposition increase, shifting the species composition towards more thermophilic and eutrophic communities. 4. Synthesis. We hypothesize that the release from abiotic constraints (milder temperature and higher nitrogen availability) due to global changes and long-standing extensive grazing counteracting the negative effects of nitrogen deposition have been responsible for the diversity and compositional changes of plant communities over the last decades in the Pyrenees. Thus, in contrast with other grasslands, high-elevation grazed grasslands may increase in species diversity with nitrogen deposition under climate warming., This work was funded by the French Environment and Energy Management Agency (ADEME; ANEMONE project No. 1262C0013), the Communaute de Travail des Pyrenees through the Region Midi-Pyrenees (ANEMONE project No. 11051284) and Aragon (ANEMONE project No. CTPP13/11) and the Observatoire Homme Milieux Pyrenees (OHM) du Haut Vicdessos. This work was supported by the French Laboratory of Excellence project 'TULIP' (ANR-10-LABX-41; ANR-11-IDEX-0002-02).

National audience

The objective of this paper is to develop a framework for pedogenetic modelling in the Anthropocene, i.e., the present geological epoch during which humanity has become the main factor impacting the environment. We review the concepts of soil evolution as well as 15 existing quantitative models to determine the features of soil evolution modelling in an Anthropocene context. We emphasise soil-plant interactions by considering the importance of vegetation, both as a provisioning service and as a factor in soil evolution. Our review covers output variables, time scales, spatial representation, model structure, and control variables. Our synthesis in this work demonstrates that the modelling of pedogenesis in the Anthropocene requires the following specific features: (i) a description of the human impact on soil evolution, (ii) outputs related to ecosystem functions and services, (iii) the integration of a dual time scale (decade and cyclic shorter-term), (iv) multiple and interactive processes modelling, (v) the simulation of vegetation and its feedback on soils, and (vi) a representation of spatial heterogeneities, at least at the profile scale. No specific models of soil evolution in the Anthropocene have been developed thus far; however, certain required characteristics have been integrated into existing soil-plant models. Some others features will require further development, particularly a coherent and tested conceptual cornerstone that enables dual-time-scale modelling and is based on the resilience concept and energy metrics. We thus propose a general framework as a conceptual basis from which we can develop models of pedogenesis in the Anthropocene.

French landscapes are submitted to increasing anthropogenic pressures. These pressures can affect plant species diversity by modifying the quality and spatial configuration of habitats, including forest habitats. This project addressed the role of the composition and configuration of the forest and non forest landscape mosaic on forest plant diversity. It was based on 1932 plots from the National Forest Inventory located in 19 "départements" of Northern France. Landscape indices such as fragmentation were measured or calculated from aerial photographs and existing national forest maps. A specific field study was devoted to analyse the depth of the effect of a particular linear landscape feature: the forest road. Landscape patterns had a significant impact in addition to local habitat quality. Plant composition was influenced by three main landscape gradients: (1) forest or non-forest habitat, (2) presence of fellings and young stands and (3) species composition (broadleaves or coniferous). The openings in the surrounding landscape (agricultural lands, forest felling and young stands) had an effect on plants through their quantity, number of patches and edge length. This effect was positive for most species, which confirms the role of the openings in maintaining plant diversity. The species traits discriminated were epi-zoochory and anemochory, mass x length of seeds and some Grime adaptive strategies. This work also underlined the importance to analyse landscape pattern effect within a buffer zone of more than 1 km around the plots. In contrast, we found that forest roads had a short depth of edge influence on plants (< 5 m) and road effect was more often positive than negative. The mechanisms underlying the influence of landscape mosaic are discussed in light of a temporal effect on plants. The implications for habitat and forest management to protect biodiversity are presented., Les paysages français sont de plus en plus soumis aux pressions anthropiques. Ces pressions engendrent des modifications de la qualité et de la configuration des habitats, y compris forestiers, et ont des effets sur les plantes. Cette thèse aborde le rôle de la composition et de la configuration de la mosaïque paysagère extra- et intra-forestière sur la diversité de la flore en forêt. Il s'appuie sur 1932 relevés de l'Inventaire Forestier National répartis dans 19 départements de la moitié nord de la France. Les indices paysagers ont été calculés à partir de fonds cartographiques et d'images aériennes photo-interprétées. L'étude de terrain a été consacrée à la portée de l'effet d'un élément linéaire particulier du paysage : la route forestière. Le paysage a un effet important au-delà de la qualité de l'habitat local. La flore répond à trois principaux gradients paysagers : le premier est lié à la nature forestière ou non forestière du paysage, le second à la présence de coupes et peuplements jeunes, et le dernier reflète la composition en essences (feuillus ou résineux). L'effet des ouvertures paysagères (extra-forestière cultivée, coupe, peuplement jeune) sur la flore passe par la quantité, et surtout le nombre de taches et la longueur d'interfaces. Cet effet est positif sur la plupart des espèces, ce qui confirme le rôle des ouvertures dans le maintien de la diversité floristique. Les traits des espèces discriminés sont l'épi-zoochorie et l'anémochorie, la masse x longueur des semences et certaines stratégies de Grime. Ce travail montre qu'il est primordial d'appréhender le paysage sur un rayon de plus d'1 km. En comparaison, la route a un faible impact sur la flore, et plus souvent un effet positif que négatif. Les mécanismes sous-jacents à l'influence du paysage sont discutés à la lumière d'un effet temporel sur les plantes. Les implications pour la gestion des habitats en faveur de la biodiversité sont abordées.

Prix "Gourmand wine book axards France 2010", catégorie Histoire des boissons; La mise en place d'une gouvernance véritable de la production est une garantie pour maintenir les équilibres entre production et consommation. Celle-ci impose la prise en compte simultanée des échelles spatiales adaptées à chaque gestion en considérant les temporalités multiples du fonctionnement du vignoble. Cette gouvernance nécessite une excellente mémoire du vignoble, laquelle passe par une bonne gestion des archives publiques comme privées et par des études récurrentes pour tenir en éveil les différents groupes d'acteurs concernés. Ces études ne doivent pas comme trop souvent se limiter à des analyses économiques sur le court terme mais prendre en compte l'ensemble des temporalités des sociétés vitivinicoles. C'est à ce pris que l'on espérer assurer la durabilité des vignobles européens dans la concurrence mondiale.

National audience

Proceedings paper from the 9th International Symposium on Physical Measurements and Signatures in Remote SensingChinese Acad Sci, Inst Geog Sci & Nat Resource Res, Beijing, China, OCT, 2005; Thermal Infra Red (TIR) Remote sensing allow spatializing various land surface temperatures: ensemble brightness, radiometric and aerodynamic temperatures, soil and vegetation temperatures optionally sunlit and shaded, and canopy temperature profile. These are of interest for monitoring vegetated land surface processes: heat and mass exchanges, soil respiration and vegetation physiological activity. TIR remote sensors collect information according to spectral, directional, temporal and spatial dimensions. Inferring temperatures from measurements relies on developing and inverting modeling tools. Simple radiative transfer equations directly link measurements and variables of interest, and can be analytically inverted. Simulation models allow linking radiative regime to measurements. They require indirect inversions by minimizing differences between simulations and observations, or by calibrating simple equations and inductive learning methods. In both cases, inversion consists of solving an ill posed problem, with several parameters to be constrained from few information. Brightness and radiometric temperatures have been inferred by inverting simulation models and simple radiative transfer equations, designed for atmosphere and land surfaces. Obtained accuracies suggest refining the use of spectral and temporal information, rather than innovative approaches. Forthcoming challenge is recovering more elaborated temperatures. Soil and vegetation components can replace aerodynamic temperature, which retrieval seems almost impossible. They can be inferred using multiangular measurements, via simple radiative transfer equations previously parameterized from simulation models. Retrieving sunlit and shaded components or canopy temperature profile requires inverting simulation models. Then, additional difficulties are the influence of thermal regime, and the limitations of spaceborne observations which have to be along track due to the temperature fluctuations. Finally, forefront investigations focus on adequately using TIR information with various spatial resolutions and temporal samplings, to monitor the considered processes with adequate spatial and temporal scales. 10.1 Introduction Using TIR remote sensing for environmental issues have been investigated the last three decades. This is motivated by the potential of the spatialized information for documenting the considered processes within and between the Earth system components: cryosphere [1–2], atmosphere [3–6], oceans [7–9], and land surfaces [10]. For the latter, TIR remote sensing is used to monitor forested areas [11–14], urban areas [15–17], and vegetated areas. We focus here on vegetated areas, natural and cultivated. The monitored processes are related to climatology, meteorology, hydrology and agronomy: (1) radiation, heat and water transfers at the soil–vegetation–atmosphere interface [18–24]; (2) interactions between land surface and atmospheric boundary layer [25]; (3) vegetation physiological processes such as transpiration and water consumption, photosynthetic activity and CO2 uptake, vegetation growth and

Soil erosion due to rainfall is a complex phenomenon. Factors influencing erosion and subsequent transport include rainfall intensity, soil properties, topography, land cover and antecedent conditions. These factors and their interactions can be approximated in physically based models. This thesis aimed to develop new physical understanding of precipitation-driven soil erosion processes on the laboratory flume scale. Experiments were carried out using the 6-m × 2-m EPFL erosion flume. In all experiments, different surface treatments were employed, with sediment concentration data collected from the flume effluent. The experimental data were analyzed using a mechanistic process-based soil erosion model, known as the Hairsine-Rose (H-R) model, with the goal of assessing the model's ability to describe the data. The H-R model simulates an arbitrary range of sediment size classes, a feature that is crucial to describe flume-scale soil erosion in detail. A range of related phenomena was investigated, as outlined below. First, the effect of raindrop splash and transversal width of the experimental flume on soil erosion was examined. In addition, the parameter consistency of the H-R model under these conditions was tested. Results showed that the H-R model represented well the total sediment concentrations as well as those of the fine and medium sediment size classes only when the transverse width of the flume experiment was below/around a threshold value related to lateral splash length. It was found, however, that boundary condition-induced asymmetry markedly reduces the applicability of the H-R model (and likely any other erosion model). Furthermore, in common with some existing reports, it was confirmed that the H-R model does not predict well the breakthrough of larger sediment size classes, possibly because for those sediments the transport mechanism involves rolling on the bed, which is not accounted for in the model. Second, the proportionality between soil erosion and area-exposed to the raindrop splash was tested. Results revealed that under carefully controlled laboratory conditions, the cumulative eroded mass depends on the cumulative runoff, and that soil erosion is proportional to the area exposed to raindrops. However, this relationship was controlled to a smaller extent by the initial soil conditions such as moisture content, bulk density and soil surface characteristics. The sediment concentrations in the flume effluent during the initial phase of the erosion event were sensitive to the initial state of the soil surface. At steady state, it was observed that the concentration of eroded sediments were controlled mainly by the effective rainfall and area exposed to raindrops. In contrast, using published data it was shown that rain splash erosion in the field is, in general, not proportional to the area exposed. Unlike the controlled laboratory experiments, the field experiments were characterized by a non-uniform initial surface roughness, surface soil aging and heterogeneous rock fragment size and spatial distribution. The third part of this study was dedicated to investigation of the effect of rock fragments on flume-scale hydrological response and soil erosion delivery. An area-based modification of the H-R model that accounted for the rock fragment coverage was employed to analyze the experimental data. The results revealed that the rock fragments protected the soils from raindrop splash and retarded the overland flow, therefore decreasing its sediment transport capacity. Individual rock fragments prevented surface sealing beneath them, which in turn increased the overall infiltration rate and affected the development of water depth compared with bare soil conditions. At short times, rock fragments were found to affect selectively the different size classes. This is due to the delayed (compared to a bare soil) development of the overland flow depth at the commencement of the erosion event. At steady state, the rock fragments led to decreased concentrations of the individual size classes in proportion to effective rainfall and the area exposed to raindrops. It was found that the modified H-R model predictions agreed well with measured sediment concentrations when high rainfall intensity and low rock fragment coverage were used. On the other hand, the H-R model could not reproduce the details of measured sediment breakthrough curves for conditions of low rainfall intensity and high rock fragment coverage. Finally, the effects of initial soil conditions and rock fragment coverage on particle size distribution and eroded mass were investigated using multiple rainfall events. Results revealed that short-time soil erosion is sensitive to the erosion history, in particular to whether steady-state conditions were reached in the preceding erosion event. Because the largest sediment sizes take longer to reach steady state, this sensitivity was more pronounced for the larger size sediment classes. The results also showed that the presence of rock fragments on the topsoil surface reduced the time needed to reach steady state compared with bare soil. This reflects the reduction in rain splash erosion caused by rapid development of the overland flow depth (which results from the reduction of the flow cross-sectional area by rock fragments).

Pour aborder les spatio-temporalités des modes de vie et leurs imbrications, ce chapitre propose une généalogie de la notion de mobilité en sciences sociales. Après cette séquence d’histoire de la pensée, il revient ensuite sur l’appréhension des échelles spatiales et temporelles de la mobilité. Après cette exploration conceptuelle et épistémologique, il se termine par la présentation des différentes contributions qui constituent la substance de cet ouvrage.