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International audience; Assessing risks from soil pollution by trace metal (TM) elements is often perilous, since multiple human activities generally influence the nature and load of metal pollutants, and may locally disturb the soil composition and organization. Once incorporated in the soil surface horizon, metal-bearing particles are submitted to different physicochemical and biogeochemical constraints, depending on soil nature, occupation and land management. Liberated TM’s are diversely redistributed among soil surface and depth horizons, depending on the type of metal. In soils of agro- and natural ecosystems, such redistribution of TM’s is often closely related to soil forming processes. Here we present feedback the variability of TM contents in soils of two major sites in France, polluted either by industrial atmospheric fallout or by irrigation with urban wastewater. Trace metal distribution patterns were depicted at different study scales: polluted area, agricultural fields, soil profile, constituents. Our work illustrates a great number of factors that determine a TM content in a collected soil sample: extent of pollution, soil nature and behaviour, land use, specific TM properties. The importance of using pedology tools for defining sampling strategies that are well adapted to a given type of pollution and study scale is emphasized. Sound pedological expertise is ssential to assure the representativeness of soil samples and to guarantee the relevance of molecular-scale studies, a prerequisite for a valuable assessment of risks related to soil pollution by heavy metals.; L’évaluation des risques de sols pollués par les éléments traces métalliques (ETM) est délicate car l’activité anthropique interfère dans la nature et l’ampleur des apports d’ETM et peut perturber la composition et l’organisation des sols. Après l’incorporation des ETM dans l’horizon de surface, la nature, l’usage et l’occupation des sols impriment des contraintes physicochimiques et biogéochimiques sur les phases porteuses d’ETM et les éléments libérés sont redistribués au sein de l’horizon de surface et/ou entre la surface et les horizons profonds. Dans les sols d’agro- et écosystèmes naturels, les redistributions sont étroitement liées aux processus pédologiques.Ce travail présente un retour d’expérience sur la variabilité des teneurs en ETM dans deux sites majeurs français, pollués par retombées atmosphériques d’origine industrielle ou par épandage d’eaux usées urbaines. La variabilité des teneurs en ETM y est analysée à différentes échelles : du secteur pollué, au parcellaire agricole, au solum, jusqu’aux constituants particulaires. Les exemples illustrent les nombreux facteurs qui déterminent in fine la teneur en ETM d’un échantillon de sol : l’ampleur de la pollution, le lieu et la profondeur des prélèvements, le temps de résidence des ETM, la nature du sol et les conditions physicochimiques, les propriétés intrinsèques des ETM… L’emploi d’outils de la pédogenèse pour construire une stratégie d’échantillonnage adaptée au type de pollution et à l’échelle d’étude est un atout majeur dans l’étude des sols pollués. L’expertise en pédologie permet d’assurer la représentativité des échantillons et de garantir ainsi la pertinence d’études à des échelles fines, condition sine qua non pour juger valablement des dangers et risques.

National audience; This research aims to evaluate the relevance of using the diversity measurements on satellite images taking into account the problem of the MAUP (Modifiable Areal Unit Problem). We calculate a vegetation indice for an image SPOT 5 of 5 meters resolution. Then, we cut out the image into grids of different aggregated resolution. For each image, we calculate 3 diversity index: Shannon, Simpson and Dominance. We process a resampling of the observed data and design another image corresponding to the "maximal" diversity. Same calculations of diversity index are applied on these two images. We then measure the extent and the evolution of the phenomenon through the scales according to the types of images and the statistical distributions of the pixels. The results show how sensitive is the diversity assessment to the MAUP and how we may identify what we call a "pertinent scale"; Cette recherche vise à évaluer la pertinence de l'utilisation des mesures de diversité sur des images satellitaires en abordant le problème du MAUP (Modifiable Areal Unit Problem). Nous calculons tout d'abord un indice de végétation sur une image SPOT 5 de 5 mètres de résolution (image 1). Puis, nous créons une image répartissant aléatoirement ces mêmes pixels observés sur une zone de même taille (image 2). Deux images extrêmes sont également utilisées pour comparaison : une image de la diversité nulle (tous les pixels ont la même valeur, image 0) et une image de diversité « maximale » (tous les pixels sont différents, image 3). Nous découpons alors les images 1 et 2 en grilles de différentes résolutions, croissantes et imbriquées. Considérant les pixels de l'image initiale contenus dans chaque maille, nous calculons 3 indices de diversité, Shannon, Simpson et de Dominance. Les résultats présentés sont les moyennes, médianes et distributions statistiques des valeurs de diversité des mailles de chaque image. Ils permettent de mesurer l'ampleur et l'évolution de la sensibilité de ces indices à travers les échelles et selon les types d'images. Nous comparons aussi les écarts et les rapports entre les valeurs des diversités des trois séries. Les résultats permettent d'introduire et de discuter le concept d' « échelle pertinente »

The interactions of genetically modified (GM) crops with soil species and ecosystems is complex, requiring both specific and broad spectrum assessments. In the ECOGEN project we undertook experiments at three scales of increasing complexity, using Bt maize expressing the Cry1Ab protein from Bacillus thuringiensis as an example. Test species were selected for laboratory-scale experiments to represent taxonomic groups that we could also monitor at glasshouse and field scales (e.g., nematodes, protozoa, micro-arthropods, earthworms, and snails). In the laboratory, single species were exposed to purified Cry1Ab protein or to Bt maize leaf powder incorporated into simplified diets under controlled conditions. In the glasshouse, multiple test species and soil microbial communities taken from ECOGEN's field sites were exposed to Bt maize plants growing under glasshouse or mesocosm conditions. In the field, evaluations were conducted on our selected indicator groups over multiple sites and growing seasons. Field evaluation included assessment of effects due to the local environment, crop type, seasonal variation and conventional crop management practice (tillage and pesticide use), which cannot be assessed in the glasshouse. No direct effects of Cry1Ab protein or Bt leaf residues were detected on our laboratory test organisms, but some significant effects were detected in the glasshouse. Total nematode and protozoan numbers increased in field soil under Bt maize relative to conventional maize, whilst microbial community structure and activity were unaffected. Field results for the abundance of nematodes and protozoa showed some negative effects of Bt maize, thus contradicting the glasshouse results. However, these negative results were specific to particular field sites and sampling times and therefore were transient. Taking the overall variation found in maize ecosystems at different sites into account, any negative effects of Bt maize at field scale were judged to be indirect and no greater than the impacts of crop type, tillage and pesticide use. Although the ECOGEN results were not predictive between the three experimental scales, we propose that they have value when used with feedback loops between the scales. This holistic approach can used to address questions raised by results from any level of experimentation and also for putting GM crop risk:benefit into context with current agricultural practices in regionally differing agro-ecosystems.

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no sp Assessment of Nitrogen Fluxes to Air and Water from Site Scale to Continental Scale; absent

National audience; Le ruissellement de l'eau de pluie à la surface des sols est la cause de l'érosion des sols et de la formation des coulées boueuses. La mise en place d'aménagements anti-ruissellement dans les bassins-versants agricoles implique de tenir compte de l'impact des sillons sur la direction du ruissellement. La collecte de données de ruissellement sur le terrain est très limitée par la difficulté de mesurer simultanément plus de quelques emplacements au sein d'un bassin versant pouvant couvrir plusieurs kilomètres carrés. C'est pourquoi une modélisation mathématique est essentielle pour compléter les approches de terrain. Nous allons présenter ici en particulier, la recherche faite dans le cadre du projet ANR METHODE, comportant une forte interaction entre hydrologues et mathématiciens. Ce projet était centré sur l'interaction ruissellement-topographie-sillons. L'analyse du problème a fait apparaître que les techniques d'homogénéisation n'étaient pas applicables car la taille caractéristique des sillons ne peut jamais être supposée petite par rapport à la profondeur de l'eau. C'est donc bien l'interaction à l'échelle des sillons qu'il faut simuler. C'est pourquoi, nous avons choisi de modéliser le ruissellement par les équations de Saint-Venant, en y ajoutant un terme de source (la pluie). De plus, la résolution doit prendre en compte simultanément la topographie générale et les sillons. Or, la taille caractéristique d'une maille hydrologique étant la dizaine de mètres de coté, il n'est pas possible de représenter explicitement les sillons (dont la largeur caractéristique est le décimètre). On doit donc se limiter, pour chaque maille, à une description macroscopique des sillons. Cette collaboration a abouti à un code (FullSWOF 2D) permettant aux hydrologues de disposer d'un outil utilisant des méthodes mathématiques récentes et à la proposition de trois méthodes pour calculer la direction du ruissellement sur une surface comportant des sillons.

International audience

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International audience

International audience; The spatial and temporal arrangement of crops is a conspicuous feature of rural landscapes. It has been identified as an important factor in many environmental issues, such as the coexistence of genetically modified (GM) and non-GM crops, and the mitigation of soil erosion. This paper examines a scenario-based approach for rapid generation and screening of crop allocations that meet user’s constraints without requiring mechanistic modelling. LandSFACTS (Landscape Scale Functional Allocation of Crops Temporally and Spatially) is a software application specifically designed to simulate such crop arrangement scenarios, whilst ensuring both spatial and temporal coherence with regard to the initial constraints. The software uses an empirical approach to allocate crops to fields (polygons in vector format) over a sequence of years, using a stochastic process (Markov chains) and rule-based constraints. Crop rotations are represented by transition probabilities complemented by other temporal constraints such as return period or prohibited sequences. Further spatial and temporal constraints on crop arrangement can be applied through separation distances, yearly proportions, and the application of statistical tests. The software outputs a crop allocation solution with a crop for every field for every year, respecting all user-defined constraints; the range of potential solutions can then be explored through multiple model runs. Metrics based upon the difficulty of obtaining such an allocation from the initial constraints are also generated. A case study is provided to demonstrate the use of combined agronomic and environmental criteria for exploring GM crop coexistence at the landscape scale.

International audience; Soil scientists are receiving increasing numbers of requests for expert advice on soil over large areas, but at a high resolution. We tested the use of the soil data contained in sources of information that are not directly accessible (referred to as ‘grey’ data) to accomplish this task. We collected grey data about a pine forest, which is currently the subject of drastic, and questionable, changes in management, including a rapid rate of biomass removal. These grey data (from 266 sites) were compared with soil data obtained directly from our field sampling (83 sites). Our comparisons showed that the two sources of data were consistent when the variables concerned had been sampled and analysed by using methods shared by the soil scientists such as particle-size distribution. Conversely, significant discrepancies appeared for variables for which different methods existed, such as for CEC. For the latter, using corrective equations gave contrasting results, depending on the soil variable. The final database was used to characterize the soils of the study region. Results showed that soils of the study region (mainly sandy podzols and arenosols) were acidic and particularly oligotrophic. Several important properties (CEC, phosphorus cycling, pH, bulk density) were related to the organic fraction or carbon (C) content of soils. For instance, CEC values were linearly and exclusively dependent on C content. The most oligotrophic sites of the study region were clearly not suitable for the new intensive management of the forest in the long term. For the other sites, the question remains open because some specific data are still needed before drawing conclusions. We conclude that as a complement to conventional soil studies, the grey literature is a useful source of data and information to characterize soils at a regional scale.

National audience

International audience; There are many incentives for applying a crop model at a regional scale, i.e. over an area larger than that for which it has been developed. This is what we call "spatialising" a crop model. These large areas can have very heterogeneous soil, climate and management practices. Consequently, spatialising a crop model can pose serious problems. One set arises from the fact that the basic concepts, hypotheses and validity domains of crop models are derived at the plot scale and may not apply at a larger scale. Another set arises from the lack of adequate and sufficient data to run the model at a regional scale. The workshop held in Toulouse (France) on 14-15 January 2002 dealt with the topic of spatialising crop models. The present paper is a comprehensive summary of the thoughts we and before, during and after the workshop.; De multiples raisons conduisent à utiliser les modèles de culture sur des surfaces supérieures à celles pour lesquelles ils ont été mis au point. C'est ce que nous désignons sous le terme de "spatialisation" des modèles de culture. Ces vastes étendues présentent de fortes hétérogénéités spatiales, relatives au sol, au climat et aux pratiques culturales. En conséquence la spatialisation pose un certain nombre de problèmes, qu'ils soient dus au fait que les concepts de base, les hypothèses et le domaine de validité des modèles de culture sont établis à l'échelle de la parcelle agricole et ne conviennent plus lorsque les modèles sont appliqués à une échelle régionale, ou au fait que les données d'entrée nécessaires manquent quand les surfaces considérées deviennent très vastes. Le séminaire de Toulouse des 14 et 15 janvier 2002 a abordé ce thème de spatialisation des modèles de culture. Le présent article est un résumé détaillé des réflexions conduites avant, pendant et après ce séminaire.

International audience; The d18O composition of water and CO2 exchange at smaller scales (leaf and ecosystem) can be affected by changes in atmospheric water vapour at larger (regional) scales. During a sampling campaign in a beech forest in Germany in August 2002, we encountered such a large scale change when dry sunny weather was followed by a large storm system with heavy rains leading to floods across Europe. During the transition, canopy vapour d18O decreased at least 2 permil, and the d18O composition of leaf water then reflected isotopic exchange with this depleted vapour due to the high humidity. Hence, bulk leaf water was substantially more depleted at night compared to the first, sunny period, and showed virtually no evaporative enrichment during the day. Values of 18O discrimination during CO2 exchange for photosynthesis strongly decreased from the sunny to the wet period, whereas those for nocturnal respiration increased by a factor of 2 to 4. Model simulations indicated that the small positive foliage isoflux during the day was offset by the negative isoflux at night. As a consequence, the d18O of CO2 in canopy air decreased by about 3 permil. The d18O signatures of canopy water and CO2 thus reflected the transition from local water to the regional regime of depleted water deposited across the area by the storm.

International audience

Diplôme : Dr. d'Universite

ridaura@supagro.inra.fr Seccion II. Temas estrategicos en las evaluaciones de sustentabilidad [chapitre] 7 livre de 200 p. + CD ROM interactif; International audience; Ce chapitre constitue une révision bibliographique sur la question des échelles dans l'évaluation de la durabilité des systèmes agricoles innovants. La révision bibliographique se concentre sur l'utilisation de modèles pour l'évaluation multi-échelle, ses points forts et faibles. Elle présente aussi un modèle pour l'évaluation multi-échelles qui, basé sur la programmation linaire, prend en compte l'interaction entre différents niveaux d'échelle dans l'analyse de scénarios.

The recent development of large environmental databases allow the analysis of the ecological behaviour of species or communities over large territories. Solar radiation is a fundamental component of ecological processes, but is poorly used at this scale due to the lack of available data. Here we present a GIS program allowing to calculate solar radiation as well locally as at large scale, taking into account both topographical (slope, aspect, altitude, shadowing) and global (cloudiness and latitude) parameters. This model was applied to the whole of France (540 000 km(2)) for each month of the year, using only a 50-m digital elevation model (DEM), latitude values and cloudiness data. Solar radiation measured from 88 meteorological stations used for validation indicated a R(2) of 0.78 between measured and predicted annual radiation with better predictions for winter than for summer. Radiation values increase with altitude, and with slope for southern exposure, excepted in summer. They decrease with latitude, nebulosity, and slope for north, east, and west exposures. The effect of cloudiness is important, and reduces radiation by around 20% in winter and 10% in summer. Models of plant distribution were calculated for Abies alba, Acer pseudoplatanus, and Quercus pubescens, for France. The use of solar radiation improved modelling for the three species models directly or through the water balance variable. We conclude that models which incorporates both topographical and global variability of solar radiation can improve efficiency of large-scale models of plant distribution., Le développement récent d’importantes bases de données phytoécologiques permet l’analyse du comportement des espèces ou des communautés sur de larges territoires. Le rayonnement solaire est une composante essentielle du fonctionnement des écosystèmes, mais il est peu utilise a cette échelle du fait du manque de données disponibles. Nous présentons un programme élaboré sous SIG permettant de calculer le rayonnement aussi bien localement que sur de vastes espaces, prenant a la fois en compte des paramètres locaux (pente, exposition, altitude, effet de masque) et globaux (latitude, nébulosité). Ce modèle a permis de calculer le rayonnement solaire sur l’ensemble de la France (540 000 km2), pour chaque mois de l’année, en utilisant seulement un Modèle Numérique de Terrain (MNT) de 50 m de résolution, des valeurs de latitude et des données de nébulosité. Les radiations solaires de 88 postes météorologiques ont été utilisées pour la validation, le R2 entre le rayonnement annuel prédit par le modèle et celui mesure sur les postes météorologiques s’établissant a 0,78, avec de meilleures prédictions pour l’hiver que pour l’été. Les valeurs de radiations augmentent avec l’altitude, et la pente pour les expositions sud, hormis en été. Elles diminuent avec la latitude, la nébulosité, et la pente pour les expositions nord, est et ouest. L’effet de la nébulosité est important et réduit le rayonnement d’environ 20 % en hiver et 10 % en été. Des modèles de distribution ont été calcules pour trois essences, Abies alba, Acer pseudoplatanus, et Quercus pubescens, pour la France. L’utilisation du rayonnement solaire améliore les trois modèles, directement ou a travers la variable de bilan hydrique. Nous concluons qu’un modèle de rayonnement solaire qui inclut a la fois la variabilité topographique et des facteurs plus globaux, est approprie pour améliorer l’efficacité des modèles de distribution des plantes réalisés a large échelle.

International audience; Crops are allocated to their fields by growers according to rotational principles and such rotations may be defined and classified. Rotations evolve through the aggregate choices of crops by growers over time which create the characteristic agricultural landscapes for a given region. As agriculture becomes ever more competitive, growers increasingly should use such rotational principles to maximise efficiency. Their choices of crop allocations alter the observed temporal heterogeneity and spatial pattern of cropped landscapes. Within the European Union the forms of heterogeneity studied here are increasingly evident at the landscape scale. We present techniques to study these patterns of crops in time and space. This is essential in order to build realistic simulators of large-scale cropped landscapes within which farming practices may be studied across national boundaries. Simulation is required to provide realistic arenas to extend current models of gene flow from the field to the landscape scale, in furtherance of studies of coexistence between genetically modified and conventional and organic crops. We provide simple, empirical descriptors of cropped landscapes in terms of the degree of the non-randomness of the allocation. Non-randomness of fields is assessed in terms of (i) spatial pattern, (ii) temporal heterogeneity, and (iii) spatio-temporal heterogeneity. Four formal statistical tests of significance are presented: one of spatial pattern, two of temporal heterogeneity and one of spatio-temporal heterogeneity that may also be used to test for spatial pattern. The tests were exemplified using data taken from a study landscape of 72 arable fields farmed by 10 different growers in Burgundy, France, from 1994 to 1997. Two of the tests were based on simple χ2-statistics; two were randomisation tests. The χ2-test of spatial pattern demonstrated clustering in the distribution of set aside fields. The χ2-test of temporal heterogeneity demonstrated non-randomness for eight growers who employed 15 rotations. The randomisation test of temporal heterogeneity found significant non-randomness for one grower in three of the five crops examined. The common 3-year rotation of oilseed rape, wheat, winter barley was employed by one grower on 10 of their fields, for which significant spatio-temporal heterogeneity was shown by the proposed randomisation test. It is possible to extend the analysis of these test-statistics between – and within – units in a hierarchy, so that the methods could be used to study pattern at larger scales than landscapes, say at regional or national scales.

Cet article introduit les nouveaux besoins en information spatialisée générée par les techniques d'agriculture de précision. Il rappelle mes différentes méthodes d'intervention des techniques culturales prenant en compte ou cherchant à atténuer la variabilité des caractères du milieu physique. Il souligne l'importance de la variabilité temporelle dans toute analyse spatiale impliquant l'étude des transferts (eau, énergie). L'analyse montre que le besoin d'information à des échelles fines implique la mise en oeuvre de recherches méthodologiques comme le développement de nouveaux moyens de prospection, l'adaptation des méthodes d'interpolation statistiques (pour l'estimation des variables et aussi de leur incertitude) ou la valorisation des données exhaustives disponibles. Des recherches plus fondamentales sont également envisagées avec notamment une meilleure connaissance des structures et des fonctionnements du milieu physique aux échelles fines (du dm2 à quelques m2). Cette analyse des besoins en information conduit à élargir le thème de l'agriculture de précision à celui de la "gestion spatialisée des agro-systèmes". Dans une dernière partie, quelques travaux publiés dans cet ouvrage sont mis en regard des prospectives de recherches énoncées.

Le problème que pose la présente étude est celui de la prise en compte du coût relatif des enfants par rapport à celui des adultes et des économies d'échelles dans l'appréciation du bien-être des ménages. Les résultats issus des échelles empiriques construitent à cet effet montrent que les ménagent dirigés par les femmes sont plus pauvres que ceux dirigés par les hommes. La pauvreté est plus ambiante dans les zones rurales, dans les ménages dont le chef est analphabète et dans les ménages dont le chef exerce dans le secteur informel. En ce qui concerne la dynamique, les résultats montrent que la pauvreté a augmenté au Cameroun entre 1996 et 2001. Bien que certains résultats confortent ceux issus des échelles "Recommended Dietary Allowances" (RDA) utilisés par l'institut national de la Statistique, d'autres les remettent en question. Les résultats de l'étude recommandent la mise en oeuvre de politiques spécifiques pour la réduction de la pauvreté., The purpose of the study is to investigate the integration of the relative cost of children to parents and of economies of scales in the context of the evaluation of household welfare. Results derived with empirically-estimated scales show that households headed by women are poorer than those headed by men. Poverty is also found to be more prevalent in rural areas, in households whose heads are illiterate, and in households whose heads works in the informal sector. As for poverty dynamics, the results show that poverty increased in Cameroun between 1996 and 2001. Despite the fact that some results are the same with those derived from the Recommended Dietary Allowances (RDA) scales used by Cameroon's National Institute of Statistics, many stand in stark contrast to these. The results of the present study are used to recommend specific policies in favour of poverty alleviation.

International audience; Agricultural policies are increasingly replaced by agro-environmental and rural-development polices. The rationale behind this evolution is that the policies seek to enhance the sustainability of agricultural systems and contributions from these systems to sustainable development at large. The same can be argued for agricultural innovations; they are increasingly aimed at serving a range of sustainability objectives, rather than only improving productivity and quality. As a result, resource use issues related to agriculture must be analysed and addressed from an integrated and multi-scale perspective. Both the introduction of alternative agricultural resource use options and agro-environmental policies would benefit from their ex ante assessment. Contributions from agronomy to such integrated assessment have strong implications for its research agenda. This chapter presents an extensive example of a multi-scale assessment methodology (SEAMLESS) in which agronomy plays a significant but partial role. The methods allow the investigation of different kinds of policies and innovations and their effects on economic, environmental and social objectives of stakeholders and decision makers at farm, regional and sector level

International audience; The monitoring of earth surface dynamic processes at a global scale requires high temporal frequency remote sensing observations which are provided up to now by moderate spatial resolution sensors. However, the spatial heterogeneity within the moderate spatial resolution pixel biases non-linear estimation processes of land surface variables from remote sensing data. To limit its influence on the description of land surface processes, corrections based on the quantification of the intra-pixel heterogeneity may be applied to non-linear estimation processes. A complementary strategy is to define the proper pixel size to capture the spatial variability of the data and minimize the intra-pixel variability. This work provides a methodology to characterize and quantify the spatial heterogeneity of landscape vegetation cover from the modeling of the variogram of high spatial resolution NDVI data. NDVI variograms for 18 landscapes extracted from the VALERI database show that the land use is the main factor of spatial variability as quantified by the variogram sill. Crop sites are more heterogeneous than natural vegetation and forest sites at the landscape level. The integral range summarizes all structural parameters of the variograin into a single characteristic area. Its square root quantifies the mean length scale (i.e. spatial scale) of the data, which varies between 216 and 1060 in over the 18 landscapes considered. The integral range is also used as a yardstick to judge if the size of an image is large enough to measure properly the length scales of the data with the variogram. We propose that it must be smaller than 5% of the image surface. The theoretical dispersion variance, computed from the variograin model, quantifies the spatial heterogeneity within a moderate resolution pixel. It increases rapidly with pixel size until this size is larger than the mean length scale of the data. Finally based on the analysis of 18 landscapes, the sufficient pixel size to capture the major part of the spatial variability of the vegetation cover at the landscape scale is estimated to be less than 100 m. Since for all the heterogeneous landscapes the loss of NDVI spatial variability was small at this spatial resolution, the bias generated by the intra-pixel spatial heterogeneity on non-linear estimation processes will be reduced.

International audience

International audience; The monitoring of earth surface dynamic processes at a global scale requires high temporal frequency remote sensing observations which are provided up to now by moderate spatial resolution sensors. However, the spatial heterogeneity within the moderate spatial resolution pixel biases non-linear estimation processes of land surface variables from remote sensing data. To limit its influence on the description of land surface processes, corrections based on the quantification of the intra-pixel heterogeneity may be applied to non-linear estimation processes. A complementary strategy is to define the proper pixel size to capture the spatial variability of the data and minimize the intra-pixel variability. This work provides a methodology to characterize and quantify the spatial heterogeneity of landscape vegetation cover from the modeling of the variogram of high spatial resolution NDVI data. NDVI variograms for 18 landscapes extracted from the VALERI database show that the land use is the main factor of spatial variability as quantified by the variogram sill. Crop sites are more heterogeneous than natural vegetation and forest sites at the landscape level. The integral range summarizes all structural parameters of the variogram into a single characteristic area. Its square root quantifies the mean length scale (i.e. spatial scale) of the data, which varies between 216 and 1060 m over the 18 landscapes considered. The integral range is also used as a yardstick to judge if the size of an image is large enough to measure properly the length scales of the data with the variogram. We propose that it must be smaller than 5% of the image surface. The theoretical dispersion variance, computed from the variogram model, quantifies the spatial heterogeneity within a moderate resolution pixel. It increases rapidly with pixel size until this size is larger than the mean length scale of the data. Finally based on the analysis of 18 landscapes, the sufficient pixel size to capture the major part of the spatial variability of the vegetation cover at the landscape scale is estimated to be less than 100 m. Since for all the heterogeneous landscapes the loss of NDVI spatial variability was small at this spatial resolution, the bias generated by the intra-pixel spatial heterogeneity on non-linear estimation processes will be reduced.

National audience; En France, sous l’effet de la décentralisation et de l’ouverture de l’Europe, au Canada avec les fusions municipales, mais aussi dans les pays du sud avec le désengagement des États, de nouveaux lieux de décision et d’action sont mis en scène. Différents acteurs interviennent pour gérer le territoire, acteurs locaux et institutionnels, partenaires publics et privés, représentants de l’État, élus des collectivités territoriales, professionnels ou société civile. Les secteurs d’activités concernés et les niveaux où celles-ci s’organisent sont multiples. Les activités sont donc à prendre en compte et à intégrer dans toutes leurs dimensions tant économiques que sociales, écologiques que culturelles pour l’accompagnement de l’action et la formation des acteurs. Les « territoires » sont ainsi collectivement construits, dans leur matérialité comme dans leur valeur symbolique, via des processus innovants. La participation des acteurs et la multiplicité des échelles spatio-temporelles en jeu sont les ingrédients de base des recompositions territoriales résultantes. La nature de ces recompositions est plurielle : elle est organisationnelle, dans la mesure ou il s’agit de coordonner des actions à différents niveaux et de combiner différentes logiques ; elle est aussi spatiale, car les actions génèrent de nouvelles entités spatiales de gestion (et une légitimité des acteurs correspondante) et produisent de nouvelles configurations ; elle est enfin cognitive, car de nouvelles visions du territoire émergent et les représentations des acteurs évoluent. Ces constats imposent de développer de nouveaux concepts, méthodes et outils pour accompagner ces processus dans leur diversité et leur complexité. Une convergence de recherches Depuis plusieurs années s’est structuré en France un ensemble de chercheurs, agronomes, géographes, aménageurs travaillant sur les « Modèles spatiaux pour le développement territorial ». Ces derniers se proposent d’analyser les représentations spatiales produites dans des dispositifs où chercheurs et acteurs sont confrontés à des questions de développement territorial (Lardon et al., 2001). Au-delà des premières expériences mises en commun, deux nouvelles ouvertures sont apparues nécessaires. La première concerne la prise en compte des représentations des acteurs et leur implication dans les projets. Elle ouvre sur les questions de participation et d’appropriation des approches (Debarbieux et Lardon, 2003). La seconde ouverture est liée au développement des nouvelles technologies de l’information et de la communication (NTIC) et à la mise en évidence de l’utilité de ces outils dans de nombreux domaines, y compris celui de l’action territoriale (Mainguenaud, 2002).

This article reviews viticultural zoning concerns and issues, from a worldwide perspective. The needs of the everexpanding international wine market, and thus zoning objectives, have seen significant changes in recent years. Consequently, more countries and individual wine-producing regions have been involved in zoning studies. Although many of these studies were initiated in Europe, zoning needs reach far beyond the countries endowed with centuries-old viticultural history. The demarcation of registered designations of origin or protected geographical indications is one of the most obvious zoning aims. Viticultural zoning originated in the XIXth century in Europe, but is now widely applied in even the most recent emerging wine-growing countries of the New World. Other important zoning aims, not necessarily related to demarcating operations, often involve segmenting a vineyard territory into homogeneous units for pest management, land division, vineyard-restructuring operations, harvestquality management or site selection for new vineyards. The homogeneous units obtained through viticultural zoning are frequently referred to as ‘terroirs’. However, their spatial scale and the qualitative and quantitative methods of analysis may vary greatly, depending on the individual authors and the characteristics of the vinegrowing region, and consequently it is difficult to make international comparisons. Viticultural zoning studies can be divided broadly into two main approaches: the first approach is based largely on the geographic differentiation of wine, grape, or grapevine characteristics, while the second approach focuses on the geographical differentiation of land capability or vineyard suitability studies in which soil and climate are normally the key environmental variables used with varying degrees of importance. Although viticultural zoning is not always synonymous with mapping and spatial analysis, this practice is changing due to the enhanced use of geomatics. For example, digital mapping methods and remote sensing techniques have revolutionized viticultural zoning on all levels, ranging from the single plot to the regional level. On the field or local scale, the suitability approaches may include precision viticulture, which is mostly directed towards an understanding of grapevine ecophysiological functioning. On the regional or global scale, suitability approaches may be oriented towards the characterisation of broad geographical patterns of land use. The challenge with the different approaches is to compare the results derived at the regional level with those of the sample sites on the local scale. This paper provides some examples of the various approaches that are likely to enable zoning comparisons at the various spatial scales, including the international level.

Connectivity is a key concept of landscape ecology as it relates to flows and movements of organisms as driven by landscape structure. More and more aspects of landscape heterogeneity are considered in measuring connectivity, as the diversity of crops in agricultural landscapes. In this paper, we explored the value of considering changes and cumulated effects of connectivity over time. As an example, we analysed connectivity among patches influenced by maize over 7 years in an agricultural landscape in Brittany, France. Clear temporal patterns appeared: maize is concentrated in certain parts of the landscape, but over the period the whole area, 70% of the landscape, used for maize was connected. Instead of discrete patches, maize may produce large clusters allowing movement from patch to patch from year to year. This reinforces the importance of understanding land use allocation rules within farms and landscapes to evaluate the ecological effects of agriculture. (c) 2005 Elsevier Ltd. All rights reserved.

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International audience; A computer-based economic model of arable, forestry and silvoarable systems was developed as part of the ‘Silvoarable Agroforestry for Europe’ project. The process of developing the model is described in terms of: the model background and purpose, the systems modelled, the objective of the economic analysis, the viewpoint of the analysis, the spatial and temporal scales, the generation and use of biophysical data, the model platform and interface, and the inputs and outputs. The objectives of the economic analysis are to compare silvoarable, arable and forestry systems at a one-hectare scale, and to determine the feasibility of silvoarable systems at a farm-scale. At a one-hectare scale, a partial budget is used to undertake a discounted cost-benefit analysis. The farm-scale analysis allows for heterogeneous land types, multiple enterprises on each land type, phased planting, and farm fixed costs. The model runs on an annual time step and requires biophysical data. It operates in a commonly available spreadsheet and works in different European language versions of the software. The description of the model and the process of development should be useful for future users and those embarking on their own modelling projects. This research was carried out as part of the SAFE (Silvoarable Agroforestry for Europe) collaborative research project. SAFE is funded by the EU under its Quality of Life programme, contract number QLF5-CT-2001-00560, and the support is gratefully acknowledged.

National audience; Notre objectif est de modéliser la présence d'espèces d'oiseaux en fonction de descripteurs paysagers. Nos données sont des cartes (sens large) et des points géoréférencés où différentes espèces ont été recensées. Ces données nous amènent à considérer plusieurs types d'échelles qui peuvent varier. Une échelle est déterminée par un grain et une étendue, elle peut être spatiale, temporelle et thématique. Les espèces perçoivent leur milieu à différentes échelles, c'est à dire que ce qui est distinct pour l'une ne l'est pas forcément pour d'autres. La description du paysage et les observations d'oiseaux peuvent se faire à différentes échelles. La recherche d'un modèle optimal nécessite de tester plusieurs combinaisons de ces échelles. Nos résultats montrent l'intérêt de cette approche multi-scalaire pour améliorer les modèles, mais aussi pour comparer l'influence respective des types d'échelles considérés.

By sampling plant species in a Mediterranean grassland, the authors examine the influence of the study scale on : (i) the detection of ecological gradients by the correspondence analysis, and (ii) the validation of one of the two models : core-satellite hypothesis or Kolasa’s model. These models concern the frequency distribution of species. The size of the quadrats varies from 1.56 to 100 m2. Results show that the study scale does not influence the detection of the principal ecological gradient. Nevertheless, species with high contribution to factorial axes change as study scale varies. Authors relate this fact to the abundance variability of individuals of a species according to the «point» of a gradient. On the other hand, results on a small scale are consistent with Kolasa’s model, and on a large scale they are consistent with the core-satellite hypothesis. The discussion underlines the role of quadrats size in the character «core» or «satellite», and the «saturation » of large quadrats in certain species. Whatever the scale, a large category of species are infrequent (present in few quadrats). This shows that the mechanisms which lead to a weak frequency of species (mass effect, survival in favourable patches...) are essential whatever the scale., Grâce à un échantillonnage des espèces végétales dans une pelouse méditerranéenne, les auteurs étudient l’influence de l’échelle d’étude sur : (i) la détection de gradients écologiques au moyen de l’analyse factorielle des correspondances, et (ii) la validation de l’un des deux modèles : le modèle «core-satellite » ou le modèle de Kolasa. Ces modèles concernent la distribution des fréquences des espèces parmi les relevés. La taille des relevés varie de 1,56 à 100 m2. Les résultats montrent que l’échelle d’étude n’a pas d’influence sur la mise en évidence du principal gradient écologique. Cependant, les espèces à forte contribution ne sont pas les mêmes lorsque l’échelle d’étude change. Les auteurs expliquent ce fait par la variation de l’abondance des individus d’une espèce à un point du gradient. D’autre part, le modèle de Kolasa est compatible avec l’échantillonnage des petits quadrats, et le modèle «core-satellite » est compatible avec l’échantillonnage des grands quadrats. La discussion souligne l’importance de la taille des relevés sur le caractère «core» ou «satellite» d’une espèce, et la saturation des grands relevés en certaines espèces. Quelle que soit l’échelle, beaucoup d’espèces ne sont pas fréquentes (présentes dans peu de relevés). Cela montre que les mécanismes qui sont responsables de la faible fréquence d’une espèce (effet de masse, survie dans des «taches» favorables) sont essentiels quelle que soit l’échelle envisagée., Madon Olivier, Gachet Sophie, Barbero Marcel. Influence of study scale on the characterisation of plants community organisation in a Mediterranean grassland (Mont Ventoux, France). In: Ecologia mediterranea, tome 25 n°2, 1999. pp. 205-214.

National audience; Temperature variability at the urban surface is difficult to assess solely from in-situ measurements. The global coverage of satellite sensing allows to document the surface characteristics, to measure their temperature gradient, and to estimate some variables of the energy balance. Satellite multi-sensors observations over Marseilles (June 4 to July 13, 2001) and Paris (August 2003 heat wave) are used to analyze the spatio-temporal variability of urban surface temperatures. Thermal statistics are constructed from NOAA-AVHRR image series and interpreted as a function of the surface land uses and physical properties, derived from SPOT-HRV images. In the Paris region, the data reveals: a significant nocturnal heat island in downtown, related to built density and lack of evapo-transpiration; and multiple daytime thermal anomalies scattered over industrial suburbs, related to solar radiation, unobstructed field of view and thermal inertia of the surfaces. The nighttime images confirm the impact of high minimum temperatures on the heat wave process. In Marseilles, the temperature gradient also varies according to the distance to the sea and to its breeze regime. These results demonstrate the relevance of satellite remote sensing to analyze the physical processes that determine the urban climates, and to ensure their surveillance and the control of their impact; En 2007, nous avons présenté des résultats de recherche permettant de formuler l'hypothèse de l'existence possible d'une « échelle pertinente » de mesure de la (bio)diversité (Mahfoud et al., 2007). Cette approche est aujourd'hui rediscutée à la lumière de nouveaux apports de la recherche qui montrent que dans certains cas et pour certaines variables et distributions observées, il est très délicat de fixer une échelle pertinente. Nous présentons en complément une analyse exploratoire de la robustesse1 des indices de diversité de Shannon et de Simpson. Nous dégageons de ces nouveaux éclairages une discussion plus générale sur la sensibilité des indices statistiques aux effets du support2 spatial, et l'impact prépondérant de la robustesse statistique sur les mesures de biodiversité

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