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[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; In contrast to plant-animal interactions, the conceptual framework regarding the impact of secondary metabolites in mediating plant-plant interference is currently less well defined. Here, we address hypotheses about the role of chemically-mediated plant-plant interference (i.e., allelopathy) as a driver of Mediterranean forest dynamics. Growth and defense abilities of a pioneer (Pinus halepensis) and a late-successional (Quercus pubescens) Mediterranean forest species were evaluated under three different plant interference conditions: (i) allelopathy simulated by application of aqueous needle extracts of Pinus, (ii) resource competition created by the physical presence of a neighboring species (Pinus or Quercus), and (iii) a combination of both allelopathy and competition. After 24 months of experimentation in simulated field conditions, Quercus was more affected by plant interference treatments than was Pinus, and a hierarchical response to biotic interference (allelopathy < competition < allelopathy + competition) was observed in terms of relative impact on growth and plant defense. Both species modulated their respective metabolic profiles according to plant interference treatment and thus their inherent chemical defense status, resulting in a physiological trade-off between plant growth and production of defense metabolites. For Quercus, an increase in secondary metabolite production and a decrease in plant growth were observed in all treatments. In contrast, this trade-off in Pinus was only observed in competition and allelopathy + competition treatments. Although Pinus and Quercus expressed differential responses when subjected to a single interference condition, either allelopathy or competition, species responses were similar or positively correlated when strong interference conditions (allelopathy + competition) were imposed.

Understanding the interactions between bedload transport and morpholdynamics in braided streams has important applications in river management and restoration. Direct field measurements addressing this question are however scarce as they are often challenging to perform. Here, we report an extensive two-month field campaign in an Alpine braided reach (La Severaisse river, French Alps) that experienced predictable daily peak discharge (48 events observed) generating significant bedload transport and morphological changes during the melting season. We monitored these processes using a wide range of direct and indirect techniques (bedload sampling, continuous seismic measurements, pebbles tracking, topographic surveys, remote sensing using ground control cameras and drone flights). Doing so, surrogate measurements allowed to extend temporally discrete manual bedload sampling, and to extend spatially local riverbed cross section measurements. These measurements provide unique complementary constraints on the targeted physics, at various spatial and temporal scales which enabled us to draw robust conclusions. Data showed a progressive decrease in bedload transport for a given flow rate along the two months period. Simultaneously, river morphology in the braided sections changed from an incised to a more distributed configuration which led to a decrease of local maxima in dimensionless shear stresses in the braided reach for similar flow conditions. This control of bedload transport by maximum local shear stresses was in line with tracked pebble surveys indicating that coarse bedload particles were mostly transported in the main active channel. At the reach scale, this transport was found to be more efficient in laterally confined sections than in braided ones which has important implications in terms of bedload estimation in alternative confined and braided (unconfined) rivers. Finally, this study highlight the interest to combine a large variety of traditional and innovative measurements techniques to better understand complex sediment transport processes in the field.

[Departement_IRSTEA]Territoires; International audience; Environmental impact assessment (EIA) is performed to limit potential impacts of development projects on species and ecosystem functions. However, the methods related to EIA actually pay little attention to the landscape-scale effects of development projects on biodiversity. In this study we proposed a methodological framework to more properly address the landscape-scale impacts of a new stadium project in Lyon (France) on two representative mammal species exemplary for the endemic fauna, the red squirrel and the Eurasian badger. Our approach combined species distribution model using Maxent and landscape functional connectivity model using Graphab at two spatial scales to assess habitat connectivity before and after development project implementation. The development project had a negative impact on landscape connectivity: overall habitat connectivity (PC index) decreased by-6.8% and-1.8% and the number of graph components increased by +60.0% and +17.6% for the red squirrel and the European badger respectively, because some links that formerly connected habitat patches were cut by the development project. Changes affecting landscape structure and composition emphasized the need to implement appropriate avoidance and reduction measures. Our methodology provides a useful tool both for EIA studies at each step of the way to support decision-making in landscape conservation planning. The method could be also developed in the design phase to compare the effectiveness of different avoidance or mitigation measures and resize them if necessary to maximize habitat connectivity.

International audience; Chemical interactions in forested ecosystems play a role in driving biodiversity and ecosystem dynamics. Plant phenolics released by leaching can influence surrounding plants and soil organisms such as bacteria, fungi or arthropods. However, our knowledge about such chemically-mediated biotic interactions in Mediterranean oak forests is still limited, in particular whether they play a role in the limited forest regeneration. In this study, we analyzed how phenolics of Cotinus coggygria, a dominant shrub of Mediterranean downy oak (Quercus pubescens) forests, influence understory herbaceous plant species, downy oak regeneration and soil organisms in order to obtain a more integrative view of possible direct and indirect interactions triggered by this shrub species. We performed a series of experiments testing the effect of aqueous extracts of C. coggygria, mimicking natural leachates, on these organisms. Cotinus coggygria contained a high quantity of phenolics in green and senescent leaves but much less in leaf litter. Extracts from C. coggygria leaves stimulated bacterial communities, exhibited few effects on both saprophytic and symbiotic fungi, and negatively affected Collembola. Herbaceous species growth was particularly impaired by extracts from green and senescent leaves, although these effects were alleviated in the presence of soil microorganisms. In both greenhouse and field experiments, C. coggygria affected early oak seedling establishment in particular through a reduced root growth, but exhibited no effect on later seedling and sapling growth. We discussed the implication of these results for the balance between competition and facilitation in oak forests and concluded that C. coggygria has the potential to strongly alter biotic interactions, understory plant diversity and oak forest dynamics.

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[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; Wildfires burn N450,000 ha of forest every year in Euro-Mediterranean countries. Many fires originate in the Wildland Urban Interface (WUI) where housing density and weather conditions affect fire occurrence. Housing density is determined by long termland use policies while weather conditions evolve quickly. The first objective was to quantify the impacts of land use policy onWUI characteristics and fire risk in SE France during 1990–2012. The second objective was to quantify how Fire Weather Index (FWI) is related to fire occurrence. WUI was mapped from 1990, 1999, and 2012 building layers and crossed with a NDVI derived vegetation layer. In all, 12 WUI categories were derived: 4 building density classes and 3 vegetation layers. The I87 FWI was based on daily temperature, wind speed, relative humidity and soil water content. Despite a 30% increase in the number of new buildings,WUI area increased by only 5% as new housing filled in open space in existingWUI area. This trend can be linked to national level urban planning legislation and forest fire protection laws. Major driver variables determining housing location were aspect, slope, and distance to city centers. Fire frequency and burned area were nonlinearly related to FWI: 73% of the 99 fires occurred during weeks with FWI values ≥90 even though these accounted for only 44% of all weeks. Burned area was even more sensitive to FWI since 97% of total burned area occurred during weeks with mean FWI values ≥90. All days with burned areas N100 ha had FWI values N150. The study demonstrated that WUI legislation can be an efficient tool to limit WUI fire risk. FWI results suggest the predicted increase in extreme summer heat events with global warming could increase burned area as firefighting resources are stretched beyond capacity.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; The Alpine area is particularly sensitive to climatic and environmental changes that might impact socio-ecosystems and modify the regime of natural hazards. Among them, wildfire is of major importance as it threatens both ecosystems and human lives and infrastructures. Wildfires result from complex interactions between available vegetation fuels, climate and weather, and humans who decide of the land use and are the main source of fire ignitions. The changes in fire weather during the past decades are rather unknown in the French Alps especially due to their complex topography. Moreover, local institutions and managers wonder if the ongoing climate changes might increase fire risk and affect the environmental quality and the different ecosystem services provided by the mountain forests. In this context, we used the national forest fires database together with daily meteorological observations from 1959 to 2015 to investigate the changes in wildfire danger in the French Alps. We analysed the spatial and temporal variations in terms of intensity, frequency, seasonality and window of opportunity of two fire weather indices: the fine fuel moisture code (FFMC) and the fire weather index (FWI) that measure the daily water content of vegetation and the potential intensity of fires, respectively. Our results showed a major contrast between Southern Alps with a high fire weather danger on average and a significant increase in the past decades, and Northern Alps with low to moderate danger on average that increased only at low elevations. This study contributes to the understanding of the consequences of ongoings climate changes on wildfires in the French Alps. It produced high resolution results that account for the topographic and climatic variability of the area. Finally, the maps of the different fire weather components have practical implications for fire management and modelling and for preventing indirect effects of fires on ecosystems and human assets.

International audience; Natural hazards are frequent in mountain areas where they regularly cause casualties and damages to human infras-tructures. Mountain forests contribute in mitigating these hazards, in particular rockfalls. Assessing the protective effect of a forest against rockfall is a difficult task for both forest managers and rockfall experts. Accurate and simple tools are therefore required to efficiently evaluate the level of protection that results from the presence of forest. This study defines three novel indicators to quantify the protective effect of forests against rockfalls, regarding 1) the reduction of the frequency of rockfalls, 2) the reduction of their maximum intensity, and 3) the combination of the reduction of the frequency and the energy of the rocks. The first two indicators are relevant for rockfall experts whereas the third is mostly interesting for foresters as it summarizes the protective effect of forest. The Rockyfor3D model was adapted and used to simulate rockfalls propagation on 3886 different forest stands located in all the French Alps. The results of the simulations were used to calculate the three indicators for each forest stand. Finally, the relations between the forest structures and compositions and the indicators values were investigated. Our principal result shows that only three forest characteristics are required to accurately predict the indicators and evaluate the protective level of a forest against rockfall. The two first variables correspond to the basal area and the mean diameter at breast height (DBH) of the forest stand which are two parameters commonly used by forest managers. The third characteristic is the length of forest in the maximum slope direction which can be computed with a geographic information system (GIS). The method proposed in this study is easily reproducible and is suitable to evaluate the protective effect of European mountain forests at different scales. At local scale, the proposed indicators can enrich rockfall studies in which forests are usually set aside to simplify the evaluation. Moreover, the indicators may find direct applications with foresters by allowing them to identify the protective level of their forest and consequently to adapt their management. Finally, the indicators are convenient to perform spatial analysis and produce maps of the protective effect of mountain forests that could find many applications in land settlement or evaluation of ecosystem services.

International audience; Little is known about the understorey flammability of European mountain forests. The aim of this study was to determine the relative effects of climate, vegetation structure and composition on the fuel-driven variation in fire spread and intensity. Fire spread and intensity were simulated under constant moisture and weather conditions for a wide range of understorey fuel parameters measured in the litter, grass and shrub layers. Simulation outputs were used to compare understorey flammability between different forest ecosystem types (FET). The FETs were characterized by using a co-inertia analysis between composition and the environment (vegetation structure and climate). The relationships between these factors, fuel properties and understorey flammability were then tested using partial regression analyses.Results The most flammable forests displayed an open canopy (dry-subalpine and open-mediterranean) and grew in areas with dry autumns and wet and cold springs. Fire spread and intensity were controlled by the trade-off between tree cover and dead (litter) and live (grass and shrub) biomass load. Fire intensity also increased as a result of seasonal precipitation patterns (differential distribution between the seasons): rainy springs enhanced biomass growth, whereas dry climates, especially in autumn, promoted shrub biomass and stimulated litter accumulation and residence (higher litterfall and lower decomposition rates). Interestingly, we found a positive relationship between fire intensity and the proportion of conifers that disappeared after accounting for tree cover, indicating that, in the Alps, the open canopy structure of needle-leaved forests makes them potentially more flammable than broad-leaved forests because of the higher load and continuity of surface fuels. Main conclusions Inter-relationships between tree cover, precipitation seasonality and species composition govern the understorey flammability of mountain forests. We also found evidence that tree cover strongly constrains fire spread by driving the amount and type of surface fuel, which suggests that land use change can have a strong influence on flammability patterns .; On connaît peu l'inflammabilité du sous-étage dans les forêts de montagne européennes. Le but de cette étude était de déterminer les effets relatifs du climat, de la structure de la végétation et de la composition du combustible sur la propagation et l'intensité du feu. La propagation et l'intensité des incendies ont été simulés sous humidité constante et les conditions météorologiques pour une large gamme de paramètres de combustible (litière, herbe et arbustes). Les sorties de simulation ont été utilisés pour comparer entre les sous-bois d'inflammabilité types d'écosystèmes forestiers différents (FET). Les FET ont été caractérisés en utilisant une analyse de co-inertie entre la composition et l'environnement (structure de la végétation et le climat). Les relations entre ces facteurs, les propriétés du carburant et sous-bois inflammabilité ont ensuite été testées en utilisant des analyses de régression partielle. Les forêts les plus inflammables affichent un sous-bois clair et poussent dans les zones avec des automnes secs et humides et des printemps frais. La propagation et l'intensité des incendies ont été contrôlés par le compromis entre couvert d'arbres et de morts (litière) et en direct (herbe et arbuste) charge de la biomasse. L'intensité du feu a augmenté en raison de la configuration des précipitations saisonnières (répartition différentielle entre les saisons): printemps pluvieux amélioré la croissance de la biomasse, tandis que les climats secs, surtout en automne, favorisent la biomasse d'arbustes, l'accumulation de la litière et sont temps de résidence (litière plus élevée et la décomposition inférieure les taux). Nous avons trouvé une relation positive entre l'intensité du feu et la proportion de conifères qui a disparu après comptabilisation de la couverture forestière, ce qui indique que, dans les Alpes, la structure des forêts conifères les rend potentiellement plus inflammables que les forêts feuillues en raison de la charge plus élevée et la continuité des combustibles de surface. Les inter-relations entre le couvert forestier, les précipitations saisonnières et la composition des espèces régissent l'inflammabilité du sous-bois des forêts de montagne. Nous avons également constaté que la couverture forestière contrôle fortement le feu par la quantité et le type de combustible de surface, ce qui donne à penser que l'utilisation des terres peut avoir une forte influence sur les modèles d'inflammabilité.

International audience; The role of forests in the mitigation of natural hazards has been repeatedly demonstrated. The protective effect of mountain forests against rockfalls has especially been pointed out because it can constitute a natural and cost-effective protection measure in many situations. However, this particular ecosystem service may substantially differ according to the structure and the composition of the forest. Until now, the rockfall protection capability has always been studied at a local scale with only few forest types. Moreover, the comparison of the protective effect of the different forest types studied remains difficult because different methods and indicators were used. For the same reasons, it is not possible to draw conclusions about the influence of biological and structural diversities on the protection capabilities of forests from former works. The aims of this study were (1) to quantitatively assess the protective effect of forests at the French Alps scale and build a classification based on the protection capability, (2) to compare the protective effect of the different forest types present in the French Alps and (3) to analyse the relations between the protective effect and the forest diversity in terms of stand structure and tree composition. For this purpose, the model Rockyfor3D was used to simulate the propagation of rocks on 3886 different forest plots spread over the whole French Alps. Quantitative indicators characterizing the protective effect of each forest plot were then calculated from the simulation results and used to perform the different analyses. Our results emphasized the importance of taking into account the length of forest in the maximum slope direction for an accurate assessment of the protective effect. Thus, the minimum length of forest to get a reduction of 99% of the rockfall hazard was chosen as indicator to compare protective effect between forests. Using this indicator, half of the French Alpine forests presented a high level of protection after a short forested slope (190 m). A decreasing gradient in the protection capabilities was observed from forest types dominated by broadleaved species to those dominated by conifer species. Moreover, considering an equivalent proportion of conifers, stands dominated by shade-tolerant tree species showed better ability to reduce rockfall hazard. Finally, our study highlighted that a high biodiversity and a structural heterogeneity within the forest have a positive effect on the reduction of rockfalls hazard.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Resprouter species are important for Mediterranean ecosystem resilience, but they are scarce in landscapes dominated by pioneer pines. Sound knowledge of resprouter seedling functional responses and establishment success across different pine habitats would help guide forest restoration efforts. Four broadleaved resprouter species, that is two shrubs - Arbutus unedo and Pistacia terebinthus - and two trees - Fraxinus ornus and Sorbus domestica - were planted under an experimentally created gradient of pine cover from totally open conditions to dense pine cover. Seedling survival and growth were monitored for 5years. Phenological, physiological and morphological traits were measured to gain insight into the mechanisms of pine-seedling interaction. Interaction outcomes varied according to species identity, pine cover treatment and time. Light-to-moderate pine cover induced greater height growth and little or no effects on diameter and survival of the two trees. Competition was always detected for shrubs, whereas competition and facilitation were noted for trees. Within pine stands, negative interactions increased with tree cover, making dense stands the most limiting. Interactions were only detectable after 2-3years, but increased in intensity with time. Functional responses to increasing pine cover indicated a seedling strategy of carbon gain optimization in the shade (increased specific leaf area and leaf area, decreased leaf dry matter content), particularly in tree species seedlings. Increasing pine cover induced higher water stress, but lower photochemical stress. The deciduous species had a longer vegetation season under pine canopies, whereas the evergreen shrub Arbutus unedo showed a lower polycyclism rate and flower production.Synthesis and applications. Moderate pine cover facilitates the establishment of deciduous trees at the expense of shrubs. This pattern can be attributed to a higher shade tolerance of the trees than the shrubs combined with a low tolerance of trees to photoinhibition. We therefore recommend using evergreen shrubs for the restoration of open land and high-specific-leaf-area deciduous trees for pine stand diversification. However, in dense forests, thinning is needed to increase light availability prior to seedling introduction. Moderate pine cover facilitates the establishment of deciduous trees at the expense of shrubs. This pattern can be attributed to a higher shade tolerance of the trees than the shrubs combined with a low tolerance of trees to photoinhibition. We therefore recommend using evergreen shrubs for the restoration of open land and high-specific-leaf-area deciduous trees for pine stand diversification. However, in dense forests, thinning is needed to increase light availability prior to seedling introduction.

International audience; Past fire recurrence impacts the vegetation structure, and it is consequently hypothesized to alter its future fire behaviour. We examined the fire behaviour in shrubland-forest mosaics of southeastern France, which were organized along a range of fire frequency (0 to 3-4 fires along the past 50 years) and had different time intervals between fires. The mosaic was dominated by Quercus suber L. and Erica-Cistus shrubland communities. We described the vegetation structure through measurements of tree height, base of tree crown or shrub layer, mean diameter, cover, plant water content and bulk density. We used the physical model Firetec to simulate the fire behaviour. Fire intensity, fire spread, plant water content and biomass loss varied significantly according to fire recurrence and vegetation structure, mainly linked to the time since the last fire, then the number of fires. These results confirm that past fire recurrence affects future fire behaviour, with multilayered vegetation (particularly high shrublands) producing more intense fires, contrary to submature Quercus woodlands that have not burnt since 1959 and that are unlikely to reburn. Further simulations, with more vegetation scenes according to shrub and canopy covers, will complete this study in order to discuss the fire propagation risk in heterogeneous vegetation, particularly in the Mediterranean area, with a view to a local management of these ecosystems. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Past fire recurrence impacts the vegetation structure, and it is consequently hypothesized to alter its future fire behaviour. We examined the fire behaviour in shrubland-forest mosaics of southeastern France, which were organized along a range of fire frequency (0 to 3–4 fires along the past 50 years) and had different time intervals between fires. The mosaic was dominated by Quercus suber L. and Erica–Cistus shrubland communities. We described the vegetation structure through measurements of tree height, base of tree crown or shrub layer, mean diameter, cover, plant water content and bulk density. We used the physical model Firetec to simulate the fire behaviour. Fire intensity, fire spread, plant water content and biomass loss varied significantly according to fire recurrence and vegetation structure, mainly linked to the time since the last fire, then the number of fires. These results confirm that past fire recurrence affects future fire behaviour, with multi-layered vegetation (particularly high shrublands) producing more intense fires, contrary to submature Quercus woodlands that have not burnt since 1959 and that are unlikely to reburn. Further simulations, with more vegetation scenes according to shrub and canopy covers, will complete this study in order to discuss the fire propagation risk in heterogeneous vegetation, particularly in the Mediterranean area, with a view to a local management of these ecosystems.; La combustibilité de 51 placettes correspondant à différentes récurrences d’incendies depuis 1959 (0 à 4 feux) a été analysée en Provence siliceuse. Les écosystèmes étudiés sont des suberaies dominées par Quercus suber L., et des maquis à Erica arborea L. et à cistes. Les données descriptives de la végétation combustible (composition, biomasse, recouvrement, hauteur) ont été entrées dans un modèle physique du feu (Firetec) afin d’obtenir des variables descriptives du comportement de feu. Les pertes en masse et en eau de la végétation, la vitesse de propagation et l’intensité du feu augmentent de façon significative avec la continuité verticale du combustible, qui dépend principalement du temps depuis le dernier feu, puis du nombre de feux. Les résultats confirment l’hypothèse selon laquelle le feu est particulièrement intense et rapide dans des peuplements multi-stratifiés à forte charge en éléments fins et forte connexion spatiale entre les individus, tels que les maquis hauts développés après un seul feu intense en cinquante ans. Au contraire, le feu ne se propage pas dans les forêts de chênes submatures n’ayant pas brûlé depuis au moins cinquante ans et caractérisées par une faible connectivité verticale entre la canopée et le sous-étage, favorisant ainsi un effet « auto-protecteur » contre les incendies futurs. Ces informations permettent de discuter de la gestion de la végétation, en particulier la surveillance ou le débroussaillement local des maquis hauts grandement combustibles, pour diminuer le risque de propagation des feux à l’échelle de la parcelle.

National audience; Les infrastructures linéaires de transport et leur emprise (ILTe) constituent des corridors facilitant ou ralentissant les circulations d’espèces. Le développement des espèces exotiques envahissantes est généralement lié aux mouvements anthropiques et peut donc être favorisé par la présence et la gestion de ces ILTe. Classées parmi les pires espèces exotiques envahissantes d’Europe et d’Amérique du Nord, les renouées exotiques se développent sur les ILTe et soulèvent des enjeux importants en termes économiques et environnementaux (gestion, sécurité, biodiversité etc.). Des sommes importantes sont ainsi investies pour leur gestion, avec peu de retours sur l’efficacité des différentes méthodes utilisées ou sur le rôle de ces méthodes dans la dynamique paysagère de ces espèces. Le présent projet vient dans la continuité de recherches menées à Irstea Grenoble et à l’ENS de Lyon et sera mené avec l’appui de l’expertise du bureau d’étude Concept Cours d’Eau, il a pour objectifs finalisés la mise à disposition :- d’une méthode opérationnelle d’analyse et de cartographie diachronique des renouées à l’échelle paysagère - de retours d’expériences et de préconisations de gestion à l’échelle paysagère. Sur le plan scientifique, le projet permettra une meilleure connaissance des dynamiques spatiale et temporelle des renouées invasives à l’échelle paysagère, leurs modalités de gestion en lien avec leur perception par les différents acteurs, et la biodiversité spécifique et fonctionnelle des écosystèmes environnants. Il s’agit d’étudier sur plusieurs années les facteurs majeurs de développement spatiotemporel des populations de renouées, soit :- Leurs modalités de gestion qui elles-mêmes sont dépendantes de leur perception par les acteurs- Les facteurs de milieu (biotiques et abiotiques) à l’échelle locale et paysagère - Les nouvelles contaminations majoritairement liées à l’activité humaine Le couplage d’outils de télédétection, relevés et enquêtes de terrain fournira des informations sur la perception et la dynamique paysagère des renouées en lien avec la biodiversité et les corridors écologiques environnants. Cette étude sera menée en parallèle sur deux ILTe, les emprises de voies ferrées (avec l’appui de RFF) et de voies navigables (avec l’appui de VNF), elle s’appuiera sur l’examen individuel et sur la comparaison de paysages modèles de ces deux types d’infrastructures.

XIV World Forestry Congress, Durban, ZAF, 07-/09/2015 - 11/09/2015; International audience; Management strategies, using thinning combined or not combined with underplanting, have been tested in experimental forests of Spain and southern France to promote growth, recruitment and increase their resilience. In dry and fire-prone areas of southern Spain and France, Pinus halepensis forests were thinned at different levels and hardwood species were introduced under pine canopy and in opened areas. Thinning activities increased light, modified microclimate and soil moisture availability. Growth was improved in all sites but survival showed a more contrasted response. In mountainous areas, thinning treatments applied on Abies alba forests of southern France and Pinus nigra forests of central Spain were tested. Thinned silver fir stands showed higher tree growth than the control stands. In black pine forests, maximal seedling emergence was found for high basal area values whereas survival and growth were the highest for lower values. Despite strong site differences, thinning to a basal area around 15-20 m2/ha appeared to be a good compromise to promote growth of the residual stand and recruitment. In fire-prone areas, thinning, alone or combined thinning with the introduction of resprouting hardwood species, is an efficient technique but has to be adapted to site conditions and species under focus. Finally, we discussed usual thinning limitations and options of remediation in the light of the new opportunity opened by the increasing demand in forest biomass.

IUFRO - Landscape Ecology Conference, Tartu, EST, 23-/08/2015 - 30/08/2015; International audience; Landscape connectivity plays an important role in biodiversity conservation. Hence, the maintenance of ecological networks has been promoted in conservation planning from continental to local spatial scales. We propose a methodological framework combining habitat suitability and spatial graph modelling to identify and prioritize areas that contribute to ecological networks at meso-scale. Within a 200km² study area, located in south-eastern France, we collected environmental data (topography, land cover and vegetation type) and recorded bird, plant and butterfly species in 160 plots. For each taxonomic group, we selected a set of species with different ecological requirements and dispersal capacities. For each species, we used MaxEnt to model the ecological niche and the presence probability map over the whole study area. From these maps, we (i) identified suitable habitat patches and (ii) estimated landscape resistance to species movements. Then, spatial graphs were built in Graphab using habitat patches as nodes and least-cost paths derived from landscape resistances as links between these nodes. The contribution of each node and link to habitat network connectivity was estimated. Finally, all species graphs were combined to generate a multi-species ecological network diagnosis.

International audience; Climate change is a major concern on forest: how will the current stand response to this change? Plant architecture is a science that allows studying the morphology of plants. Under contrasted climate (such as temperate climate), plant growth is not continuous: there are several breaks (particularly in winter). For several species these breaks remain visible for many years (leaving marks like scars). Black spruce (Picea mariana Britton., Stern & Poggenb. 1988) follows this pattern. We then studied architecture from mixed stand (Parc des Grands jardins, Québec) in order to assess the climate response of Black spruce architecture. We studied these parameters: -annual shoot length -ramification -needle length -reproduction For each parameter, we computed a PLS (Partial least square) regression (linear or logistic) with climatic parameters (monthly rainfall and temperature) and topologic variables (such as ramification order, age …). The results of this analysis allow finding the active periods (organogenesis and elongation). We aggregated this result to build a simulator of Black spruce development depending on a climatic scenario.

International audience; Linear elements: - Not sufficient to preserve butterfly communities Woodlands: - Positive effect even on grassland specialists Species of conservation concern most impacted: - Homogenization of communities Connectivity metrics: - Using multiple metrics help to understand population/community functioning

International audience; The green and blue infrastructure in France is based on the conservation and restoration of ecological continuity of habitats in relation to species’ biological requirements. Recent development in landscape ecology based on graph theory and species movement modelling using least-cost paths offer promising applications in terms of landscape management and biodiversity conservation. First, we present the model of potential connectivity based on graph theory and explain why it overcomes previous approaches. Then, we illustrate with an example of connectivity analysis in the region PACA for the Red Squirrel, a forest generalist species. The models identify the landscape areas that are connected or isolated from the rest of habitat network and prioritize the importance of patches and corridors for the maintaining of global network connectivity; they also analyse how connectivity varies according to species dispersal distance. They highlight the key habitat patches and corridors that must be protected to maintain habitat network connectivity for the species. These examples clearly show that these original methods can form valuable decision support tools for the implementation of green infrastructures at different spatial scales, and also help to locate further finerscale studies.

National audience; Le maintien, voire la restauration de la connectivité écologique sont l'une des préoccupations majeures pour les politiques publiques d'aménagement du territoire et de conservation de la biodiversité en réponse à la perte et à la fragmentation des habitats naturels semi-naturels engendrées par l'augmentation des pressions anthropiques. La question centrale pour l'aménagement du territoire est la suivante : où doit-on agir de manière efficace au niveau d'un territoire pour maintenir ou restaurer un réseau écologique ? Les différentes méthodes de modélisation de la connectivité au sein d'un réseau écologique permettent de procéder à une modélisation plus ou moins réaliste des processus (connectivité structurelle, potentielle, réelle), mais qui va de pair avec la quantité et la précision des données d'entrée, le temps de formalisation et la durée de calcul nécessaires. Parmi ces méthodes, nous avons privilégié les graphes paysagers couplées à la modélisation des déplacements d'espèces par les chemins de moindre coût, car ils intègrent à la fois des indices d'habitat spatialement explicites et des données sur la dispersion des espèces, permettant l'étude de la connectivité potentielle. La vision adoptée est celle d'un réseau d'habitats pour une région donnée dont on cherche à mesurer la connectivité pour une espèce (ou un ensemble d'espèces), c'est-à-dire la quantité d'habitat atteignable par l'espèce. Les graphes paysagers offrent sans doute le meilleur compromis entre les données d'entrée des modèles et la qualité et la richesse de l'information fournie à la sortie. Cependant, les graphes paysagers, comme d'autres méthodes (e.g. théorie du circuit) ont l'inconvénient d'être des modèles "déterministes". D'autres approches comme les modèles de populations spatialement explicites (SEPM) permettent d'étudier la dynamique de la population, mais nécessitent beaucoup de données de départ (taux de dispersion, taux de mortalité) et sont donc plus lourds en termes de modélisation. Nous présentons ces deux approches en détaillant les intérêts et limites respectifs dans un objectif de planification territoriale à but de conservation de la biodiversité à différentes échelles spatiales. Même si peu de travaux ont comparé les deux approches, ils ont conclu qu'elles présentaient les mêmes performances et que la théorie des graphes apportait même dans certains cas des informations supplémentaires. Nous soulignons enfin les verrous qui limitent l'application pratique des outils de modélisation actuels, notamment nos faibles connaissances sur les capacités de dispersion des espèces.

National audience; Les gradients d’abondance d’espèces depuis la périphérie vers le coeur des massifs forestiers (ou effet lisière) sont souvent considérés comme le résultat de filtres environnementaux. Nous avons testé l’hypothèse que les changements passés du paysage, i.e. l’usage ancien du sol et la distribution spatiale des forêts anciennes (sans défrichement depuis 1830) et des forêts récentes (défrichée pour être cultivée ou pâturée avant 1830 puis reboisé depuis) au sein des massifs forestiers actuels, expliquaient mieux ces gradients. Nous avons compilé sur 11936 relevés floristiques de la moitié nord de la France des données climatiques, pédologiques et dendrométriques, l’ancien usage du sol et des variables paysagères actuelles et passées, en utilisant les BD IGN-Ifn et les cartes d’État-major de 1830. Nous avons analysé par régression logistique la réponse de 181 plantes de sous-bois à l’usage ancien du sol et au paysage actuel et passé, tout en contrôlant les autres sources de variation (sol, climat, peuplement). Nous montrons que les forêts récentes sont situées en moyenne à plus faible distance de la lisière actuelle du massif que les forêts anciennes. La réponse des espèces à la distance à la lisière actuelle correspond à leur réponse à l’usage ancien du sol : les espèces de coeur préfèrent les forêts anciennes et les espèces de périphérie les forêts récentes. La distance à la lisière forestière de 1830 explique mieux la distribution des espèces que la distance à la lisière actuelle ou que l'usage ancien du sol. Le gradient coeur-périphérie des plantes de sous-bois est donc bien expliqué par le paysage passé et les processus de colonisation et de recrutement. Cela suggère que les différences de composition des communautés entre l’intérieur et la périphérie des massifs forestiers sont davantage liées à une limitation par la dispersion et à la compétition qu’à des filtres environnementaux.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [TR2_IRSTEA]RIVAGE; International audience; Background and Aims. Tree root system structure and development are difficult to assess and poorly understood in natural conditions because of soil heterogeneity and the difficulty in extracting mature tree root systems without damaging them. The purpose of this study was to understand root system development plasticity according to biological and physical parameters: species tree age and size, soil material, water availability, slope angle, and climate. Methods. Two hundred and forty-three mature trees from twelve species were uprooted from homogeneous French dikes fills. Root system structure (root number and size, root system span, depth and volume) was compared between two contrasting soil materials: fine and coarse. Results.Tree species had little influence on root system structure: all root system types and root size could be found for most of the species according to site conditions. Heart root systems were limited to fine material while mixed and tap root systems were found on coarse material. In coarse materials, trees developed few but rather large roots (> 5 cm in diameter and >4 m in length). In fine materials, root systems had three times more roots but they were 40% smaller and shorter. Roots were 20% more numerous and 65% larger on the downslope side due to water availability at dike or riverbank toe. Conclusion. Root system structure was mainly influenced by soil material and water availability and far less by tree species. Tree root systems are opportunistic in developing in the direction where water and nutrients are plentiful: whatever the species, predicting its dimensions and structure requires a thorough investigation of soil and other environmental conditions. This study gives a new insight in root development: it will help predict tree root growth in various environments and particularly on dikes.

International audience; Aims: This study aimed at disentangling the respective influence of species, environment, root size and root type in tree root architecture.Method: The root system of 106 adult trees from ten species was carefully extracted from French dikes. Root length and proximal diameter, length and diameter of root segments and branch insertion diameter were measured. Root branching and tapering rates, segment taper, classical (P) and new architectural parameters related to branching patterns were computed.Results: Two contrasting root types called "running" (R) and "short" (S), were identified from growth and architectural parameters. Compared to S roots, R roots were longer for an equivalent proximal diameter and singled out with lower tapering rate, branching rate and segment taper and with smaller branches. Their main axis lost less in diameter at branching point for branches of the same size. Tree species had little influence on these architectural parameters. The effect of soil material (coarse vs fine) was significant mainly on root size, on branching rate in fine material, and only secondarily on some branching patterns for running roots and on segment taper. The new architectural parameters describe branching patterns more accurately than classical ones.Conclusion: This study provides an original insight in tree root architectural analysis, proposing a new root typology and innovative parameters for the description and modelling of root architecture.

National audience; Les incendies de forêts sont une partie intégrante des écosystèmes méditerranéens. Ils constituent à la fois une menace pour les biens, les services et les écosystèmes, en détruisant chaque année des milliers d’hectares. Bien qu’il existe encore des incertitudes liées aux projections climatiques, les décideurs publics et les gestionnaires devront probablement faire face à une augmentation de la fréquence des incendies, de leur intensité et de leur sévérité.

2015 International Congress on Ultrasonics, Metz, FRA, 10-/05/2015 - 14/05/2015; International audience; The aim of this study was to find a relevant criterion to detect and map tree roots in the surrounding soil. In each experiment, we studied properties of propagation, especially velocity and attenuation of amplitude, as parameters to discriminate the roots from the soil. Our work was initiated by laboratory experiments with an ultrasonic transmission device to highlight relative differences between samples of soil and roots. Measurements were repeated on different root samples (species, dimension, decomposition time) to cover the diversity encountered on dikes. Then an intermediate state device reproducing in-situ conditions in laboratory was performed at the soil surface in two plastic containers: one control with only soil and another containing a buried root sample . We shown with laboratory experiments that information provided by the velocity term seems relevant to localize roots in the soil for healthy root samples. The study in containers gave similar results, significant variations of velocity being observed due to root presence.

L’urbanisation et les activités humaines croissantes ont entraîné une rupture de la continuité paysagère. Cette fragmentation induit une diminution brusque des flux de gènes entre populations et métapopulations d’espèces animales et végétales, compromettant leur survie. Ces changements paysagers (perte d’habitats d’intérieur, isolation des taches d’habitats…) impliquent de développer des outils dans le cadre de l’établissement d’une Trame Bleue et Verte. Dans cette optique l’établissement de graphes paysagers intégrant l’écologie des espèces (capacité de dispersion et modèle de niche) et les caractéristiques du paysage, permettent de modéliser l’importance des taches et des liens dans la connectivité globale du réseau. Cette approche permet de mesurer la qualité des habitats propices à l’établissement des espèces et les chemins de moindre coût qui les relient. Ces constructions semblent robustes et nécessitent un apport d’informations moindre mais rares. Les graphes ainsi obtenus et leurs différentes représentations sont donc de bons outils d’aide à la gestion conservatoire, mais mériteraient d’être affinés par l’ajout d’information écologique sur les espèces, ce qui les rendrait plus prédictifs

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Plant architecture can be used to study plant development retrospectively thanks to time-dependent morphological markers, particularly those corresponding to the winter break in temperate regions. The Aleppo Pine and the Turkish Pine are polycyclic species, thus they usually develop several consecutive growth units per year, making it sometimes difficult to date them. In this study, we show that keeping track of the pith diameter profile, to date each shoot, is an efficient method. The pith diameter is larger on the first growth unit than on the last growth unit of the year.Moreover, a pairwise comparison showed that the pith diameter undergoes a decrease along the annual shoot from the first growth unit to the last. As pith diameter decreases upwards the annual shoot, it can be used for dating. Pith diameter progresses from 1 year to another too: there is an increase in the early years of life, corresponding to the tree's establishment phase. Lastly, we found a positive relationship between the basal pith diameter of an annual shoot and its length. The variability around this relationship could reflect environmental conditions, especially climate conditions.

International audience; Southeastern France is the most wildfire prone region of the country. To identify the main driving factors of fire density (defined as the number of fires per hectare) at the local scale (cluster of communities which are homogeneous in terms of land cover, climate and WUI) and to assess their spatial variation at this scale, the fire density was investigated in the département Bouches du Rhône using georeferenced fire ignitions. To assess relationships between fire density and explanatory factors, statistical analyses and spatial evaluation were performed on each clusters taking into account climate conditions, topography, land cover, Wildland-Urban Interface (defined as a buffer of 100 m around housing located at less than 200 m from natural vegetation), minor road and population densities as well as fire density as dependent variable. High fire density was mainly related to high proportion of WUI in the study area. The proportion of natural vegetation and steep slope were also among the most important drivers of fire density. Depending on the cluster, some biophysical factors can in turn enhance or mitigate fire density but coolest and wettest climate conditions related to highest elevations as well as low housing density always mitigated fire density. This work showed that, at the local scale, the identification of fire density driving factors could improve fire prevention as they can better be targeted.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; New Caledonia (NC) is a biodiversity hotspot sheltering terrestrial ecosystems of high ecological and conservation value including tropical dry forests, rainforests, and maquis. However, uncontrolled bushfires threaten this exceptional biodiversity. A science-based fire management policy could reduce the impact of unwanted fires and help facing climate change. However, to date, data on the location, extent, causal factors and spatial patterns of fires had not been collected. We compiled a 13-year-long (1999–2011) spatially-explicit fire database for NC using MODIS and Landsat data. Using boosted regression trees we disentangled the role of anthropogenic factors, physiography, weather and vegetation on fire activity. We also characterized the location of fires and the vegetation composition at the fire edges, in order to determine which ecosystems were especially vulnerable. Fire size distribution was typically asymmetric with many small fires (500 ha). Ignitions were preferentially located close to villages, cities or roads, at low elevation and linked to high values of fire weather index. Fires were larger at the end of the dry season and during El Niño events. Most fires were bushfires burning in savannas, thickets and maquis, while rainforests were rather ‘avoided’ by fire. However, bushfires generally propagated towards forests of high-conservation value, thus increasing the potential for forest edge erosion. As savanna-forest and maquis-forest mosaics are dominant in the landscape, we discuss the extent to which NC could become a ‘fire trap’ where fire cannot be easily extirpated. Based on our spatially-explicit information on fire activity, we make recommendations for a sustainable forest and fire management policy which would balance the traditional use of fire and the conservation of the most valuable ecosystems. In particular, it may help by reducing the damages of large and destructive bushfires ignited during drought peaks.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Wildfire has been recognized as one of the most ubiquitous disturbance agents to impact on natural environments. In this study, our main objective was to propose a modelling approach to investigate the potential impact of wildfire on biodiversity. The method is illustrated with an application example in New Caledonia where conservation and sustainable biodiversity management represent an important challenge. Firstly, a biodiversity loss index, including the diversity and the vulnerability indexes, was calculated for every vegetation unit in New Caledonia and mapped according to its distribution over the New Caledonian mainland. Then, based on spatially explicit fire behaviour simulations (using the FLAMMAP software) and fire ignition probabilities, two original fire risk assessment approaches were proposed: a one-off event model and a multi-event burn probability model. The spatial distribution of fire risk across New Caledonia was similar for both indices with very small localized spots having high risk. The patterns relating to highest risk are all located around the remaining sclerophyll forest fragments and are representing 0.012% of the mainland surface. A small part of maquis and areas adjacent to dense humid forest on ultramaficsubstrates should also be monitored. Vegetation interfaces between secondary and primary units displayed high risk and should represent priority zones for fire effects mitigation. Low fire ignition probability in anthropogenic-free areas decreases drastically the risk. A one-off event associated risk allowed localizing of the most likely ignition areas with potential for extensive damage. Emergency actions could aim limiting specific fire spread known to have high impact or consist of on targeting high risk areas to limit one-off fire ignitions. Spatially explicit information on burning probability is necessary for setting strategic fire and fuel management planning. Both risk indices provide clues to preserve New Caledonia hot spot of biodiversity facing wildfires

Sowing acorns from Mediterranean oaks is an age-old practice around the Mediterranean Rim that has been largely replaced by planting seedlings. In this article, we assess the method overall and reconsider it in the light of recent experimentation carried out notably in South-East France and in the north of Spain. First we describe the advantages and drawbacks of sowing compared to planting, followed by the basic principles for collecting, sorting and conserving the acorns. The requirements for effective sowing are then reviewed prior to considering the conditions for success in relation to damage from wildlife (rodents, herbivores, wild boar) and methods for preventing it. Finally, we define the impact of habitat on the success of sowing and the role played by vegetation and “nursing” devices. We conclude by stressing the advantages of the technique for the restoration of habitats and the improvement of their resilience.

IUFRO - Landscape Ecology Conference, Tartu, EST, 23-/08/2015 - 30/08/2015; International audience; Landscape connectivity plays an important role in biodiversity conservation. Hence, the maintenance of ecological networks has been promoted in conservation planning from continental to local spatial scales. We propose a methodological framework combining habitat suitability and spatial graph modelling to identify and prioritize areas that contribute to ecological networks at meso-scale. Within a 200km² study area, located in south-eastern France, we collected environmental data (topography, land cover and vegetation type) and recorded bird, plant and butterfly species in 160 plots. For each taxonomic group, we selected a set of species with different ecological requirements and dispersal capacities. For each species, we used MaxEnt to model the ecological niche and the presence probability map over the whole study area. From these maps, we (i) identified suitable habitat patches and (ii) estimated landscape resistance to species movements. Then, spatial graphs were built in Graphab using habitat patches as nodes and least-cost paths derived from landscape resistances as links between these nodes. The contribution of each node and link to habitat network connectivity was estimated. Finally, all species graphs were combined to generate a multi-species ecological network diagnosis.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Global climate models agree in predicting a warmer climate on most continental areas, with more frequent extreme events such as heat waves and repeated or exceptional droughts. By increasing drought stress, global warming is a direct threat to forest health and survival in all types of forest ecosystems around the world. Two physiological mechanisms can be involved, separately or simultaneously, in tree decline or mortality during these stressing events: hydraulic failure and carbon starvation. Study goals: We present a study performed as an international effort to understand the influence of climate change and extreme events on the architectural development of forest trees, mainly conifers, in several countries. We discuss its potential contribution to forest decline and die-back. Fourteen conifers and one broadleaved species from Europe, USA and Canada were studied with the same protocol. In 47 sites as a whole, nearly 11000 twigs, from 2300 branches of 470 trees were sampled between 2005 and 2014, some of them repeatedly every year or few years. Branch and trunk length growth, architectural development (branching and polycyclism rates) and reproduction were retrospectively measured from morphological markers over a period of 10 to 45 years according to species. Needle or leaf number per growth unit, size and life span were measured on a subsample of twigs. Study sites include four experimental designs with climate manipulation in controlled conditions: rain exclusion, irrigation or heating and combinations of heat and drought on one of them. A phenological survey was performed on three of them to monitor monthly tree architectural development. Study sites cover conditions going from the limit of the desert to the tree line in mountains. We developed a generic architectural model for conifer trunks or branches, based on the relationships between climate and all measured parameters of tree architecture and needles. It aims at simulating the immediate consequences and after-effects of climate stresses on tree architecture and leaf area, for 10-year periods. In both Europe and Northern America, repeated or extreme droughts, heat waves and other stresses considerably reduced tree and branch vigour for all species at all sites, leading to reduced branch length and tree height growth, low polycyclism and branching rates, shorter and narrower than normal needles or leaves, and small number of needles or leaves per growth unit. A strong reduction of the life span of leaves and needles for evergreen species was also measured. Thus a significant leaf area deficit was observed and modelled during or just after but also several years after severe stresses. Two mechanisms explained the long lasting legacies of these stresses: (i) the slow recovery of the number of active twigs, due to the twig deficit induced by a low branching rate during and after the stress, limiting the number of leaves and needles, and (ii) the persistence, for many years on some species, of the cohorts of small leaves and needles formed in the bad years. The long lasting reduction of tree leaf area may contribute to carbon shortage and, in extreme cases, to delayed die-off by carbon starvation.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; The regeneration phase is a critical step in plant population dynamics, but is still incompletely understood owing to the intricacy and complexity of the factors concerned. We investigated the role played by pine emergence, survival and growth in the recruitment process of a Mediterranean pine forest under disturbances of various intensities. Disturbances were produced by site treatments including mechanical chopping, soil scarification, and controlled fire of low or high intensity. Pine seedling emergence, survival, dimensions and the relative cover of bare soil, grasses and shrub were monitored on 580 1 m2 plots over 6 years in a mature Aleppo pine forest (Pinus halepensis Mill.). Seedlings did not emerge continuously and regularly with time, but mostly in bursts, which were particularly marked in the rainy autumnal seasons. This specific pattern defined a ‘window' of emergence characterised by the length of time during which seedlings emerged, the number of emerged seedlings and the shape of the window. Survival and growth decreased from the youngest cohort to the oldest cohort. Emergence, survival and growth did not respond in the same way to treatments and soil surface conditions. In particular, scarification treatments were most favourable to emergence, whereas the high-intensity controlled fire treatment was most beneficial to survival. Shrub cover was detrimental to emergence, but positively influenced survival and growth. We conclude that environmental factors controlling survival, emergence and growth processes differ, and that their importance varies over time. A detailed understanding of the processes involved in seedling recruitment can be helpful for selecting the types and intensities of the controlled disturbances to be applied to successfully regenerate forest stands.

International audience; Wildfire has been recognized as one of the most ubiquitous disturbance agents to impact on natural environments. In this study, our main objective was to propose a modelling approach to investigate the potential impact of wildfire on biodiversity. The method is illustrated with an application example in New Caledonia where conservation and sustainable biodiversity management represent an important challenge. Firstly, a biodiversity loss index, including the diversity and the vulnerability indexes, was calculated for every vegetation unit in New Caledonia and mapped according to its distribution over the New Caledonian mainland. Then, based on spatially explicit fire behaviour simulations (using the FLAMMAP software) and fire ignition probabilities, two original fire risk assessment approaches were proposed: a one-off event model and a multi-event burn probability model. The spatial distribution of fire risk across New Caledonia was similar for both indices with very small localized spots having high risk. The patterns relating to highest risk are all located around the remaining sclerophyll forest fragments and are representing 0.012% of the mainland surface. A small part of maquis and areas adjacent to dense humid forest on ultramaficsubstrates should also be monitored. Vegetation interfaces between secondary and primary units displayed high risk and should represent priority zones for fire effects mitigation. Low fire ignition probability in anthropogenic-free areas decreases drastically the risk. A one-off event associated risk allowed localizing of the most likely ignition areas with potential for extensive damage. Emergency actions could aim limiting specific fire spread known to have high impact or consist of on targeting high risk areas to limit one-off fire ignitions. Spatially explicit information on burning probability is necessary for setting strategic fire and fuel management planning. Both risk indices provide clues to preserve New Caledonia hot spot of biodiversity facing wildfires

Scenic landscapes are part of the global image of the Mediterranean Basin, but they are challenged by climate change in the 21st century. Vegetation levels are questioned by climate scenarios: although adapted to drought, plants and particularly tree species may not be able to follow the fast shift of their potential distribution area imposed by higher temperatures and rainfall decrease. In this chapter, we present the bases of present balance between climate and vegetation levels, an insight into recent evolutions of Mediterranean landscapes and some examples of early warning signs of the forecasted deep impact of climate change on these landscapes. Forest productivity should drop sharply and extensive dieback may hit forests stands on regional scale. Supported by scorching heats and severe droughts, wildfires are likely to step up in number, frequency and size. As a result of combined changes in climate and fire regimes, matorrals and steppes are expected to gain ground against wooded land, with dramatic social and economical consequences., Les paysages forestiers font partie de l'image du bassin méditerranéen, mais ils sont menacés par le changement climatique. Les étages de végétation préexistants sont remis en cause et pourraient ne pas suivre le déplacement de leurs aires bioclimatiques. Nous présentons dans ce chapitre les bases de l'équilibre actuel entre climat et végétation, les évolutions récentes, quelques exemples de signes avant-coureurs des changements prévisibles : baisses de productivité, dépérissements, extension et fréquence accrue des incendies de forêt. Des paysages de garrigue pourraient à terme remplacer les zones forestières, avec de graves conséquences sociales et économiques.

International audience; Habitat suitability ~ dispersal suitability - Dispersal constraints in population modelling Grassland & grassy strips increase dispersal Negative effect of woodlands and arable lands - Barrier for specialist low-mobile species ? Limited effect of landscape features on gene flow - Landscape connectivity good enough for this species

International audience; In agricultural landscapes, permanent grassy habitats are often fragmented and partly composed of linear elements. Landscape-level connectivity of both grassland patches and grassy linear elements actively contributes to biodiversity conservation in farmland. Nevertheless, their respective importance has rarely been tested. Butterflies form a suitable model group for this purpose; they have suffered a major overall decline in the last few decades and are known to be sensitive to landscape connectivity. We sampled 286 transects nested in 18 study landscapes in three regions. Using several metrics, we analyzed the response of butterflies to the connectivity to both grassland and woodland habitats, which may provide additional resources. The response to landscape connectivity appeared to depend on the type of the semi-natural elements (patch vs linear elements), and on species traits, i.e. the response was stronger for habitat specialists and species with low dispersal ability. We found that woody habitats close to grassland patches had a significant positive effect on butterfly communities, denoting potential mechanisms of resources supplementation and complementation. In grassy linear elements, butterfly communities were of lower conservation value, richness and abundance were much lower (- 26 and - 50%) than in grassland patches and decreased with isolation from grasslands, in line with the source–sink hypothesis. Although grassy linear elements probably play an important role in butterfly dispersal in agricultural landscapes, they may not be sufficient to preserve specialist and sedentary species. Conserving a mosaic of high quality grassland patches and woody habitats appears more effective than enhancing connectivity.

National audience; Nous présentons rapidement les principaux résultats d'un article en cours de rédaction sur le sujet.

International audience; Context: Developing silvicultural methods to help Mediterranean forests adapt to climate change is of high importance. Introducing resprouting hardwood species below pine stands is expected to promote diversity and resilience of these stands, particularly to forest fires. Aims: To examine how the intensity of pine thinning influences understory micro environment and the establishment of various hardwood seedlings in two Mediterranean sites. Methods: Aleppo pine stands were thinned down to three levels of basal area (uncut: 30 m²/ha, moderate thinning: 13-20 m²/ha, heavy thinning: 7-10 m²/ha) at two Mediterranean sites (South-East France and South-East Spain). Seedlings of six hardwood species were introduced in the understory and their survival and growth were monitored and related to changes in micro-environment induced by thinning. Results: At both sites, thinning improved light availability and seedling diameter increment of all target species. Thinning increased extreme temperature and evaporative demand. Heavy thinning increased summer soil moisture in SE Spain but not in SE France. The worst conditions for seedling survival were reached under uncut stands in SE France and low-density stands in SE Spain. Conclusion: Thinning in pine stands accelerated seedling growth but excessive thinning worsened summer drought and affected seedling survival. Moderate thinning (15-20 m²/ha) seems to be the best option in support of the introduction of hardwoods in the understory, which can improve forest diversity and resilience in the future.

International audience; no abstract

Understanding to what extent landscape conservation planning can be dependent on the spatial scale of the connectivity diagnosis is a crucial issue to support an efficient and robust implementation of the ecological network policy. We tested the robustness of connectivity diagnostics to scale impact by studying habitat patch ranking according to their importance for the conservation of the overall landscape connectivity, using 14 connectivity metrics. We analysed the influence of spatial extent, minimum mapping unit on the prioritization of habitat patches using different dispersal distances between patches. Using CORINE Land Cover 2006 data, we sampled 5 study zones in France with an extent of 11309 km² (circular buffer of radius 60 km) and diverse spatial configuration of forest patches. Our results showed that three indices (the area-weighted flux AWF, the integral index of connectivity IIC and the probability of connectivity PC) were the most robust metrics in terms of patch prioritization, while seven indices (number of links NL, number of components NC, class coincidence probability CCP, landscape coincidence probability LCP, Harary's index H, betweenness centrality BC, flux F) were less robust or even strongly scale-dependent. However, the "connector" fraction of IIC and PC, i.e. the importance of a patch as a key stepping-stone in the network (by connecting remote patches), was less robust than the corresponding overall index. In addition, the "connector" fraction of PC (PCconnector) was more robust than the connector fraction of IIC (IICconnector). We provide recommendations for an appropriate selection of connectivity indices and scale of analysis (map extent and resolution) for the implementation of green infrastructures, which should guarantee that management planning will not depend on spatial scale.; Pour accompagner une mise en oeuvre efficace et solide de la politique trame verte et bleue, un enjeu crucial est de comprendre jusqu'où les décisions d'aménagement du territoire ayant pour but de conserver la biodiversité peuvent être dépendantes de l'échelle spatiale du diagnostic de connectivité. Dans ce rapport, nous avons testé la robustesse des diagnostics de connectivité aux changements d'échelle spatiale en s'intéressant à la hiérarchisation des taches d'habitat selon leur importance pour la connectivité globale du réseau, mesurée selon 14 indices de connectivité. Nous avons analysé les effets de la taille de la fenêtre d'étude et de la résolution de la carte (grain) sur la hiérarchisation des taches d'habitats, en faisant également varier la distance de dispersion entre les taches. En utilisant la couche CORINE Land Cover 2006, nous avons échantillonné sur le territoire français 5 secteurs couvrant 11309 km² chacun (buffer circulaire de 60 km) et présentant des configurations spatiales variées en termes de taches forestières. Nos résultats montrent que trois indices (area-weighted flux AWF, integral index of connectivity IIC et probability of connectivity PC) sont les plus robustes en termes de hiérarchisation des taches, alors que sept autres indices se sont révélés moins robustes, voire très dépendants de l'échelle d'analyse. Néanmoins, la part "connecteur" des deux indices IIC et PC, c'est-à-dire l'importance d'une tache comme relais dans le réseau (permettant à des taches éloignées d'être connectées), est moins robuste que l'indice global correspondant. De plus, la part connecteur de l'indice probabiliste PC (PCconnector) est plus robuste aux changements d'échelle que la part connecteur de l'indice binaire IIC (IICconnector). Ces résultats nous permettent de proposer des recommandations pour sélectionner correctement les indices de connectivité et les échelles d'analyse (étendue et résolution des cartes) lors de l'élaboration des trames vertes, avec l'assurance que les décisions de planification seront indépendantes de l'échelle spatiale des données utilisées.

Understanding to what extent landscape conservation planning can be dependent on the spatial scale of the connectivity diagnosis is a crucial issue to support an efficient and robust implementation of the ecological network policy. We tested the robustness of connectivity diagnostics to scale impact by studying habitat patch ranking according to their importance for the conservation of the overall landscape connectivity, using 14 connectivity metrics. We analysed the influence of spatial extent, minimum mapping unit on the prioritization of habitat patches using different dispersal distances between patches. Using CORINE Land Cover 2006 data, we sampled 5 study zones in France with an extent of 11309 km² (circular buffer of radius 60 km) and diverse spatial configuration of forest patches. Our results showed that three indices (the area-weighted flux AWF, the integral index of connectivity IIC and the probability of connectivity PC) were the most robust metrics in terms of patch prioritization, while seven indices (number of links NL, number of components NC, class coincidence probability CCP, landscape coincidence probability LCP, Harary's index H, betweenness centrality BC, flux F) were less robust or even strongly scale-dependent. However, the "connector" fraction of IIC and PC, i.e. the importance of a patch as a key stepping-stone in the network (by connecting remote patches), was less robust than the corresponding overall index. In addition, the "connector" fraction of PC (PCconnector) was more robust than the connector fraction of IIC (IICconnector). We provide recommendations for an appropriate selection of connectivity indices and scale of analysis (map extent and resolution) for the implementation of green infrastructures, which should guarantee that management planning will not depend on spatial scale.; Pour accompagner une mise en oeuvre efficace et solide de la politique trame verte et bleue, un enjeu crucial est de comprendre jusqu'où les décisions d'aménagement du territoire ayant pour but de conserver la biodiversité peuvent être dépendantes de l'échelle spatiale du diagnostic de connectivité. Dans ce rapport, nous avons testé la robustesse des diagnostics de connectivité aux changements d'échelle spatiale en s'intéressant à la hiérarchisation des taches d'habitat selon leur importance pour la connectivité globale du réseau, mesurée selon 14 indices de connectivité. Nous avons analysé les effets de la taille de la fenêtre d'étude et de la résolution de la carte (grain) sur la hiérarchisation des taches d'habitats, en faisant également varier la distance de dispersion entre les taches. En utilisant la couche CORINE Land Cover 2006, nous avons échantillonné sur le territoire français 5 secteurs couvrant 11309 km² chacun (buffer circulaire de 60 km) et présentant des configurations spatiales variées en termes de taches forestières. Nos résultats montrent que trois indices (area-weighted flux AWF, integral index of connectivity IIC et probability of connectivity PC) sont les plus robustes en termes de hiérarchisation des taches, alors que sept autres indices se sont révélés moins robustes, voire très dépendants de l'échelle d'analyse. Néanmoins, la part "connecteur" des deux indices IIC et PC, c'est-à-dire l'importance d'une tache comme relais dans le réseau (permettant à des taches éloignées d'être connectées), est moins robuste que l'indice global correspondant. De plus, la part connecteur de l'indice probabiliste PC (PCconnector) est plus robuste aux changements d'échelle que la part connecteur de l'indice binaire IIC (IICconnector). Ces résultats nous permettent de proposer des recommandations pour sélectionner correctement les indices de connectivité et les échelles d'analyse (étendue et résolution des cartes) lors de l'élaboration des trames vertes, avec l'assurance que les décisions de planification seront indépendantes de l'échelle spatiale des données utilisées.

International audience; The impacts of climate change on fires are expected to be highly variable spatially and temporally. In heavily anthropized landscapes, the great number of factors affecting fire regimes further limits our ability to predict future fire activity caused by climate. To address this, we develop a new framework for analysing regional changes in fire regimes from specific spatio-temporal patterns of fires and climate, so-called pyroclimates. We aim to test the trends of fire activity and climate (1973–2009) across the Mediterranean and mountain ecosystems of south-eastern France, and to define the spatial distribution of pyroclimates. Stepwise-PCA and cluster analyses reveal that three pyroclimates capture the spatio-temporal patterns associated with fire regime and climatic conditions. Trend tests indicate a high significant increase in spring temperature and fire weather severity for most of the study area. In contrast, a general decreasing pattern of fire activity is observed since the early 1990s, specifically during summer in historically burned regions. However, winter and spring fires are becoming more frequent and extensive in less fire-prone mountains. Cross-correlation analyses indicate that inter-annual variations in extreme fire weather and fire activity were highly correlated. However, the intensity of relationships is pyroclimate-dependent. Our findings reveal that fire-climate relationships changed rapidly over space and time, presumably according to regional changes in land-use and fire policy. Assessing pyroclimates offers new perspectives for fire management and policy by delineating homogeneous zones with respect to fire, climate and their recent trends, and by revealing geographic contrasts in the underlying fire drivers.

In France, more than 10 thousand km of dikes along rivers and canals, and several thousand small dams are concerned by the tending and management of vegetation. This vegetation may contribute to their attractiveness but simultaneously call their safety into question. This book aims at filling a gap in terms of information, methods and support to managers and consultants for the management of vegetation on earthen dikes and dams. It proposes operational approaches for a comprehensive diagnosis of wooded or overgrown embankments, and to design management or rehabilitation programs aiming at guarding them against failure. Crossing multiple skills - ecology, forestry, civil works and hydraulics - this technical guide proposes a multidisciplinary approach and the synthesis of an extensive feed-back with owners, managers and public control services, based on dozens of real cases studied during 20 years.; En France, plus de 10 000 km de digues fluviales et de canaux, et plusieurs milliers de petits barrages sont concernés par l’entretien et la maîtrise de la végétation qui s’y développe. Végétation qui en constitue un attrait fort, mais qui en même temps entraîne des risques de détérioration. Ce livre comble un manque en termes d’informations, de méthodologies et d’accompagnement des propriétaires et des bureaux d’études sur la gestion de la végétation des ouvrages hydrauliques en remblai. Il apporte des méthodes opérationnelles aux professionnels du domaine pour leur permettre d’établir un diagnostic approfondi d’un ouvrage boisé ou embroussaillé, et d’élaborer un véritable plan de gestion ou un programme de travaux de confortement, garants de la sécurité des ouvrages. Au croisement de plusieurs compétences – écologie, génie civil et hydraulique –, ce guide apporte les connaissances plurielles et la synthèse d'une recherche pluridisciplinaire, tout en s’appuyant sur un important retour d’expérience issu de cas réels. Le temps de préparation de cet ouvrage - 5 ans - révèle la difficulté de cette tâche : elle est l'aboutissement d'un travail considérable, près de 20 ans d'études, et de nombreux échanges avec les gestionnaires et les administrations, pour aboutir à un manuel cohérent, clair et facile d’emploi que la profession pourra aisément s’approprier.

In France, more than 10 thousand km of dikes along rivers and canals, and several thousand small dams are concerned by the tending and management of vegetation. This vegetation may contribute to their attractiveness but simultaneously call their safety into question. This book aims at filling a gap in terms of information, methods and support to managers and consultants for the management of vegetation on earthen dikes and dams. It proposes operational approaches for a comprehensive diagnosis of wooded or overgrown embankments, and to design management or rehabilitation programs aiming at guarding them against failure. Crossing multiple skills - ecology, forestry, civil works and hydraulics - this technical guide proposes a multidisciplinary approach and the synthesis of an extensive feed-back with owners, managers and public control services, based on dozens of real cases studied during 20 years.; En France, plus de 10 000 km de digues fluviales et de canaux, et plusieurs milliers de petits barrages sont concernés par l’entretien et la maîtrise de la végétation qui s’y développe. Végétation qui en constitue un attrait fort, mais qui en même temps entraîne des risques de détérioration. Ce livre comble un manque en termes d’informations, de méthodologies et d’accompagnement des propriétaires et des bureaux d’études sur la gestion de la végétation des ouvrages hydrauliques en remblai. Il apporte des méthodes opérationnelles aux professionnels du domaine pour leur permettre d’établir un diagnostic approfondi d’un ouvrage boisé ou embroussaillé, et d’élaborer un véritable plan de gestion ou un programme de travaux de confortement, garants de la sécurité des ouvrages. Au croisement de plusieurs compétences – écologie, génie civil et hydraulique –, ce guide apporte les connaissances plurielles et la synthèse d'une recherche pluridisciplinaire, tout en s’appuyant sur un important retour d’expérience issu de cas réels. Le temps de préparation de cet ouvrage - 5 ans - révèle la difficulté de cette tâche : elle est l'aboutissement d'un travail considérable, près de 20 ans d'études, et de nombreux échanges avec les gestionnaires et les administrations, pour aboutir à un manuel cohérent, clair et facile d’emploi que la profession pourra aisément s’approprier.