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[Notes_IRSTEA]article n° 117877; International audience; The frequency, duration, and severity of drought events are expected to increase in the Mediterranean area as a result of climate change, with strong impacts on forest ecosystems and in particular individual tree growth. Tree growth response to drought is strongly influenced by local site and stand characteristics that can be quantified using competition indices (CIs) and water stress indices (WSIs). These indices have been widely used to predict tree growth; however, they are numerous, and few studies have investigated them jointly. In this context, we investigated the potential of using CIs and WSIs to investigate tree behaviour under drought. The main objective of this study was to quantify P. halepensis Mill. annual radial growth using tree size from the previous year, CIs and WSIs. We studied twelve 50-year-old Pinus halepensis plots located in the South-East of France distributed in different density treatments (light, medium and dense). At each plot, all trees were measured (height, circumference), spatialized and the ring-widths were measured for ~15 trees. We also developed a two-strata (over- and understorey) forest water balance model to simulate soil water content at a daily resolution based on stand characteristics (LAI values in particular) and soil properties. A mixed modelling approach was eventually used to investigate the drivers of P. halepensis annual radial growth and to test the performance of five CIs and four WSIs. The best growth model included tree size, the sum of Basal Area of Larger trees in a 5 m-radius (BAL; as CI), and the number of days that trees experienced water stress in a year (as WSI) as predictors. This model explained up to 56% of the variance in observed pine tree growth, which increased up to 77% when the individual tree was included as a random effect on the intercept. We found that distance-independent CIs can perform as well as distance-dependent CIs in our study site. The duration of drought alone appeared to better predict tree growth than drought intensity and duration, or drought timing. The selected model led us to reaffirm the positive effect of thinning on tree secondary growth when facing long and intense drought.

International audience; Warming and disturbance of precipitation dynamics are expected in the Mediterranean basin, resulting in longer, more intense drought and heat waves. Here we investigated how litter microbial functioning and responses to stress may be shaped by coastal environmental conditions, and whether this depends on litter type (Pinus halepensis, Pistacia lentiscus and their admixture). Mesocosms of monospecific and mixed litters collected from both inland and coastal areas were subjected to either control (25 C, 60% water holding capacity [WHC]) or stress conditions (five drying-rewetting [D/rW] cycles: 1 week of drying at 35 C, 1 week at 25 C, 60% WHC). Litters were characterised using chemical analyses (C/N ratio and solid-state 13 C nuclear magnetic resonance [NMR] spectroscopy) and indicators of microbial activity (lignocellulolytic activities, basal respiration [BR], active microbial biomass [MB], fungal and bacterial catabolic profiles). Litter type controlled cellulases and basal respiration in litters from the inland area (e.g. positive correlations between these microbial indicators and di-O-alkyl C + O-alkyl C and %N), whereas the litter-type effect was smoothed for the coastal area. Fungal and bacterial catabolic profiles were mainly shaped by the coastal conditions and litter type, respectively, indicating that fungi were more sensitive to coast-specific conditions and bacteria more sensitive to their immediate surrounding (i.e. litter type). After D/rW cycles, microbial catabolic profiles showed: (a) a stronger stress impact on microbial communities from the inland area and (b) pre-exposure to coastal constraints limited the drought effect on decomposers from the coastal area. Our findings reveal that coastal environmental conditions and litter type are major drivers of microbial functioning and responses to drought stress.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; The establishment and development of oak (Quercus spp.) seedlings are frequently impaired by siteheterogeneity resulting from historical anthropogenic disturbances in Mediterranean basin woodlands.In particular, the alteration of forest structure and soil biotic and abiotic components can compromise the natural regeneration of Persian oak (Quercus brantii Lindl.) in western Iran. This study aimed to investigate how soil properties, soil mesofauna diversity and stand structural indices differ between welland poorly regenerated areas. We sampled 105 plots in an oak woodland subjected to past disturbances but protected from human activities for the last 20 years. These 100-m2plots were distributed into two groups: i) poorly regenerated plots (PRP) with only 0 or 1 newly established oak seedling, and ii) well regenerated plots (WRP) with ≥3 seedlings. In each plot, we characterized the forest structure using three structural indices, and determined the soil properties and mesofauna diversity. Structural indices were higher in WRP than in PRP for height (0.83 and 0.23), diameter differentiation (0.74 and 0.36) and species mixture (0.90 and 0.21). Also, richness and diversity of soil mesofauna were lower in PRP than in WRP. Acanonical correspondence analysis (CCA) ordination clearly separated WRP, which were characterized by a clumped spatial distribution of mature oak trees on fertile soils, from PRP that exhibited a uniform spatial distribution of trees established on soils with a higher sand content (63 and 59%) and a higher bulk density (1.7 and 1.3). The uniform spatial distribution of trees, which was less favourable to oak seedling establishment, was inherited from intensive past human disturbances. To favour oak regeneration, we recommend applying management actions in cooperation with land-users, in particular the conservation of small patches of tree clumps to act as islands of fertility and seed sources.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Capacity matrices are widely used for assessment of ecosystems services, especially when based on participatory approaches. A capacity matrix is basically a look-up table that links land cover types to ecosystem services potentially provided. The method introduced by Burkhard et al. in 2009 has since been developed and applied in an array of case studies. Here we adress some of the criticisms on the use of capacity matrices such as expert panel size, expert confidence, and scoring variability. Based on three case-study capacity matrices derived from expert participatory scoring, we used three different approaches to estimate the score means and standard errors: usual statistics, bootstrapping, and Bayesian models. Based on a resampling of the three capacity matrices, we show that central score stabilizes very quickly but that intersample variability shrinks after 10-15 experts while standard error of the scores continues to decrease as sample size increases. Compared to usual statistics, bootstrapping methods only reduce the estimated standard errors for small samples. The use of confidence scores expressed by experts and associated with their scores on ecosystem services does not change the mean scores but slightly increases the standard errors associated with the scores on ecosystem services. Here, computations considering the confidence scores marginally changed the final scores. Nevertheless, many participants felt it important to have a confidence score in the capacity matrix to let them express uncertainties on their own knowledge. This means that confidence scores could be considered as supplementary materials in a participatory approach but should not necessarily be used to compute final scores. We compared usual statistics, bootstrapping and Bayesian models to estimate central scores and standard errors for a capacity matrix based on a panel of 30 experts, and found that the three methods give very similar results. This was interpreted as a consequence of having a panel size that counted twice the minimal number of experts needed. Bayesian models provided the lowest standard errors, whereas bootrapping with confidence scores provided the largest standard errors. These conclusions prompt us to advocate when the panel size is small (less than 10 experts), to use bootstrapping to estimate final scores and their variability. If more than 15 experts are involved, the usual statistics are appropriate. Bayesian models are more complex to implement but can also provide more informative outputs to help analyze results.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; This study assesses the effects of vegetation patterns and environmental factors on the abundance of natural tree and shrub regeneration in semi-arid forests of the Zagros Mountains, western Iran. We sampled 120 releves at different topographic positions in a protected area of the studied region. Floristic composition, slope, elevation and soil properties were recorded at each releve, and woody seedling density was measured. We have first discerned five floristic groups using two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) and then explored the relationships among the floristic group compositions, environmental factors and seedling densities. The indicator species of the 5 groups were Quercus brantii, Acer monspessulanum, Cerasus microcarpa, Rhamnus arvensis and Astragalus licyoides. Our results indicated that these groups were significantly affected by elevation and soil properties and the soil properties refer to: EC (electrical conductivity), N (nitrogen), K (potassium), OM (organic matter), and bulk density. Woody regeneration was composed of Q. brantii, A. monspessulanum, C. microcarpa, Amygdalus scoparia and Crataegus pontica seedlings. The highest density of seedlings was found for Q. brantii (97.14 (±48.00)/hm2) and the lowest for A. scoparia (2.28 (±1.50)/hm2). Quercus brantii was the dominant species and the seedling density was positively correlated with soil pH and P (phosphorus) values. A. scoparia regeneration was negatively correlated with elevation, and the seedling density peaked in C. microcarpa group. There was no significant variation in distribution of C. pontica seedlings among the groups, but the seedling density of this species was positively correlated with slope and potassium. Cerasus microcarpa seedlings were more abundant in the Q. brantii group than in other groups. This study showed that the regeneration of trees and shrub species was unequally distributed in different floristic groups for some species (A. scoparia and C. microcarpa) but not for other (Q. brantii and C. pontica) and was generally correlated with some environmental factors, particularly elevation, slope and soil nutrients (P and K). These results are a first step to implement future management and restoration strategies for promoting forest regeneration.

1. In-stream nitrate removal capacity may be used as a proxy for the ecosystem service of water quality regulation. It is well known that this natural function is driven by abiotic and biotic factors in running water environments. With regard to biotic drivers, most of the literature focuses on the microbial community influences, but there has been very little emphasis on the relationship with the benthic macroinvertebrate community. Since this community feeds on microbial assemblages (autotrophic and/or heterotrophic biofilms) that live on the streambed and in the hyporheic zone of the river, macroinvertebrates also have the potential to influence nitrate removal via its influences on microbiological processes. 2. The objective of this study was to examine the potential relationship between the macroinvertebrate communities and nitrate removal. A dataset of in-stream nitrate removal rates measured in nine-third-order streams was analysed. The simultaneous influences of abiotic (hydromorphological, physical and chemical characteristics) and biotic (biofilm and macroinvertebrate) drivers were examined and together explained 56% of the in-stream nitrate removal variance. An analysis of the independent contributions of each driver showed that abiotic drivers (e.g. ammonium, dissolved organic carbon, temperature and transient zone) contributed 40% of this nitrate removal variance, whereas the macroinvertebrate community contributed 39%. 3. The potential relationship between macroinvertebrates and nitrate removal was subsequently explored using trait-based approaches of the macroinvertebrate community. This method allows for the selection of trait modalities assuming a top-down control of microbial communities by macroinvertebrates, with in-stream abiotic conditions correlated with nitrate removal (assuming that environmental conditions affect macroinvertebrate community composition). 4. The main trait modalities positively correlated with nitrate removal were scraper (feeding habit), flagstones/boulders/cobbles/pebbles (substrate preference), crawler and interstitial (locomotion) and detritus (food). The main modalities negatively correlated with nitrate removal were silt and mud with microphytes (as substrate preference), and with fine sediment with microorganisms, and dead animals (as food sources). These results agreed with the hypothesis of top-down control and enhanced understanding of the influence of hydromorphological factors on nitrate removal. 5. This study highlights the involvement of the macroinvertebrate community in in-stream nitrate processing, and demonstrates the usefulness of applying a functional approach to explain relationships between biodiversity and ecosystem function., This study was supported by funding from the STREAMES European project (EVK1-CT-2000-00081) in the 5th Framework Programme.

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; Abiotic and biotic factors affect plants in various ways which in turn affect associated arthropod communities through direct and/or indirect bottom-up interactions. Several review articles have synthesized studies examining the indirect effects of abiotic factors on plant-arthropod interactions, mainly focusing on soil nitrogen, soil water status, and climate change. However, these studies have mostly focused on bitrophic interactions, whereas most ecological systems are composed of at least three trophic levels. Lately, research on plant-mediated multitrophic interactions in plant-arthropod food web has received increasing interest. Both the intensification of agriculture and the global climate change have the potential to trigger bottom-up effects that cascade through trophic links. In this review article, we synthesize the most recent studies describing how abiotic changes could modulate plant-mediated bottom-up forces and how it could affect arthropod communities and associated biocontrol services. We discuss potential for increasing the sustainability of managed and natural ecosystems, and highlight road maps for future studies.

[Departement_IRSTEA]Territoires [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; Changes in global fire activity are influenced by a multitude of factors including land-cover change, policies, and climatic conditions. This study uses 17 climate models to evaluate when changes in fire weather, as realized through the Fire Weather Index, emerge from the expected range of internal variability due to anthropogenic climate change using the time of emergence framework. Anthropogenic increases in extreme Fire Weather Index days emerge for 22% of burnable land area globally by 2019, including much of the Mediterranean and the Amazon. By the midtwenty-first century, emergence among the different Fire Weather Index metrics occurs for 33-62% of burnable lands. Emergence of heightened fire weather becomes more widespread as a function of global temperature change. At 2 °C above pre-industrial levels, the area of emergence is half that for 3 °C. These results highlight increases in fire weather conditions with human-caused climate change and incentivize local adaptation efforts to limit detrimental fire impacts.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Dynamiques spatiales d'anthropisation; International audience; Among plant characteristics promoting flammability, terpenes have received far less attention, especially regarding the vegetation surrounding housing. Here, mono-, sesqui-, and diterpenes were screened in live and dead leaves of ornamental species found in Wildland-Urban Interfaces (WUI) of southeastern France. Terpene content and composition were compared among species and between fuel types. Their influence on flammability was assessed through several variables and compared to that of leaf thickness and moisture content. Six of the 17 species examined contained terpenes. Terpene diversity and content differed among species but not between fuel types. Mono-, sesqui-, and diterpenes (especially the highly concentrated compounds) were involved to varying degrees in both leaf and litter flammability. Their effects could be the opposite according to the flammability variable and the fuel type considered. Leaf sesquiterpene content and litter total terpene content had the strongest influence on maximum temperature; the former also mainly drove leaf flaming duration. The other flammability variables were more strongly associated with either moisture content or leaf thickness. Our findings underlined the idea that fire management in WUI must also acknowledge the potential for ornamental species containing terpenes, such as P. halepensis, in affecting fire behaviour.

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Environmental changes such as global warming can affect ecological communities by altering individual life histories and species interactions. Recent studies focusing on the consequences of environmental change on species interactions highlighted the need for a wider, multi-species context including both trophic and non-trophic interactions (e.g. predator interference). However, the effects of biotic and abiotic factors on trophic and non-trophic interactions remain largely unexplored. To fill this gap, we combined laboratory experiments and functional response modelling to investigate how temperature and prey density influence trophic and non-trophic interactions in multiple predator communities. The system under study consisted of predatory dragonfly larvae (Aeshna cyanea) and omnivorous marbled crayfish (Procambarus virginalis) preying on common carp fry (Cyprinus carpio). We estimated the functional response of each predator in single-predator experiments and used this information to disentangle the trophic and non-trophic interactions and their dependence on environmental conditions in multiple predator trials. We found that consumer identity, prey density, and temperature all affect the magnitude of trophic and non-trophic interactions. Non-trophic interactions mostly decreased predator feeding rates, corroborating previous observations that interference prevails in aquatic communities. Moreover, trophic interactions depended primarily on the environmental variables whereas non-trophic interactions depended mainly on consumer identity. Our results indicate that non-trophic interactions among true predators and omnivores can be substantial and that biotic and abiotic conditions further modify the magnitude and direction of these interactions, which can affect food web dynamics and stability.

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes [ADD2_IRSTEA]Dynamiques spatiales d'anthropisation; International audience; The hierarchical branching nature of river networks can have a strong influence on the assembly of freshwater communities. This unique structure has spurred the development of the network position hypothesis (NPH), which states that the strength of different assembly processes depends on the community position in the river network. Specifically, it predicts that (1) headwater communities should be exclusively controlled by the local environment given that they are more isolated and environmentally heterogeneous relative to downstream reaches. In contrast, (2) downstream communities should be regulated by both environmental and dispersal processes due to increased connectivity given their central position in the riverscape. Although intuitive, the NPH has only been evaluated on a few catchments and it is not yet clear whether its predictions are generalizable. To fill this gap, we tested the NPH on river dwelling fishes using an extensive dataset from 28 French watersheds. Stream and climatic variables were assembled to characterize environmental conditions and graph theory was applied on river networks to create spatial variables. We tested both predictions using variation partitioning analyses separately for headwater and downstream sites in each catchment. Only 10 catchments supported both predictions, 11 failed to support at least one of them while in 7 the NPH was partially supported given that spatial variables were also significant for headwater communities. We then assembled a dataset at the catchment scale (e.g. topography, environmental heterogeneity, network connectivity) and applied a classification tree analysis (CTA) to determine which regional property could explain these results. The CTA showed that the NPH was not supported in watersheds with high heterogeneity in connectivity among sites. In more homogeneously connected watersheds, the NPH was only supported when headwaters were more environmentally heterogeneous than downstream sites. We conclude that the NPH is context dependent even for taxa dispersing exclusively within streams.

International audience; Pinus pinea is an important species for ecological and economic reasons in the Mediterranean area and especially in Lebanon. However, conditions of its natural regeneration have received little attention. Our study aimed to test the influence of soil disturbances, predation and autotoxicity on pine regeneration. A seed sowing field experiment was conducted in a mature stand in which two types of soil disturbances were tested (soil scarification and litter burning) in presence or absence of predation. In addition, a laboratory experiment evaluating the influence of litter (present, absent or burned) and green needle leachates (i.e. in order to mimic potential autotoxicity) on seed germination and seedling growth was conducted. Results showed a strong effect of soil disturbance, in particular soil scarification which promoted seedling emergence and early survival, whereas the role of predation was low. Forty to sixty days after seed installation, seedling density peaked at 14.9 ± 0.4 seedling.m in the scarification treatment, 13.1 ± 0.4 in the burning treatment and 8.4 ± 0.4 in the control treatment. However, an unexpected high mortality rate was recorded at the end of the field experiment in all treatments, as after seven months seedling density dropped to 0.2 ± 0.02. In the laboratory experiment, we emphasized an autotoxic effect of green needle aqueous extract on seed germination and seedling growth in the presence of litter. This allelopathic effect could be potentially linked to the presence of quinic acid which was measured as the major metabolite detected in needle aqueous extracts. In conclusion, we recommend soil preparation treatments to favour seedling emergence in combination with thinning to achieve seedling development on the long term.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; Background & Aims: Oak seedling establishment is difficult and may be partly explained by littermediated interactions with neighbors. Litter effects can be physical or chemical and result in positive or negative feedback effects for seedlings. Mediterranean species leaves contain high levels of secondary metabolites which suggest that negative litter effects could be important.Methods: Seedlings of Quercus ilex and Quercus pubescens were grown for two years in pots with natural soil and litter inputs from 6 Mediterranean woody species, artificial litter (only physical effect) or bare soil.Results: Litter types had highly different mass loss (41-80%), which correlated with soil organic C, total N and microbial activity. Litter of Q. pubescens increased soil humidity and oak seedlings aerial biomass. Litters of Cotinus coggygria and Rosmarinus officinalis, containing high quantities of phenolics and terpenes respectively, decomposed fast and led to specific soil microbial catabolic profiles but did not influence oak seedling growth, chemistry or mycorrhization ratesConclusions: Physical litter effects through improved soil humidity seem to be predominant for oak seedling development. Despite high litter phenolics content, we detected no chemical effects on oak seedlings. Litter traits conferring a higher ability to retain soil moisture in dry periods deserve further attention as they may be critical to explain plant-soil feedbacks in Mediterranean ecosystems.

International audience; Questions: How does connectivity affect animal-dispersed plant assemblages in woodlots of agriculture-dominated landscapes? Is this effect dependent on zoochorous dispersal modes? Location Long-Term Socio-Ecological Research (LTSER) site of "Zone Atelier Armorique" (ca. 150 km(2)), Brittany, western France.Methods: We sampled 26 small post-agricultural woodlots embedded in an agricultural matrix (1-7 ha). We assessed the connectivity of each woodlot using habitat reachability metrics (i.e. Proportion of Total Potential Dispersal Flux in the Landscape) calculated along a range of dispersal distances from 100 to 1,500 m. This metric was based on graph theory and was calculated as a function of landscape matrix permeability to animal movement (i.e. seed plant dispersal vectors). We analysed the composition of plant assemblages in the core and margins of woodlots. We calculated the proportion of species richness and cover of zoochorous species within these assemblages and for specific zoochorous modes (i.e. epi-, endo- and dys-zoochorous species). We analysed the effects of Proportion of Total Potential Dispersal Flux at different dispersal distances and woodlot sizes on the functional dispersal structure of the plant community using linear models.Results: We demonstrated that overall plant zoochorous assemblages only depend on woodlot size in the range of dispersal distances tested. The proportion of richness of zoochorous species within the community increased with habitat size. Connectivity influenced only the relative proportions of the different zoochorous modes, except for the dys-zoochorous group, which was primarily influenced by woodlot size. Both epi-zoochorous and endo-zoochorous species were impacted by the interaction between connectivity and woodlot area. Connectivity increased the proportion of epi-zoochorous species richness and the proportion of endo-zoochorous cover in assemblages in large woodlots. These effects were detected at short dispersal distances. Our results were supported in both total and core plant assemblages.Conclusion: This study indicates that both habitat isolation and decrease in habitat size contribute towards shaping the functional structure of the plant community, but they act at different levels of dispersal mode. Our results suggest that in these fragmented landscapes long-distance dispersal has been lost either because of the selection of small-sized animal movements or of the rareness of plant species needing large habitat size. Maintaining woodlot connectivity in the woodland surroundings seems to be sufficient to preserve short-distance dispersal, although a more thorough restoration of landscape connectivity is necessary to recover the functional composition of the community with the whole set of dispersal patterns.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; The concept of ecosystem disservices (EDS) has received much less attention than the concept of ecosystem services (ES). Using an expert-based matrix approach, we assessed the capacity of ecosystem types of the Scarpe-Escaut Regional Natural Park (France) to both provide ES and generate EDS. The matrix is a look-up table that provide for each ecosystem types a score expressing its ES capacity. Our results point to a lower capacity of the considered ecosystems to provide EDS than ES. On average the EDS scores were 60% lower than the ES scores. Of EDS, those linked to human health are the most critical, with higher capacity scores and higher expert' confidence scores than other EDS than those linked with economic or ecological impacts. We analysed correlations between ES and EDS, the presence of strong and significant positive correlations suggests that the same ecosystem characteristics, ecological functions or species groups may generate both ES and EDS. We emphasise that it is important to evaluate both EDS and ES to implement management of the ecosystems, while respecting the functioning of the ecosystems, to develop positive effects while limiting negative ones.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; In response to the negative effects of habitat fragmentation on biodiversity, habitat network conservation and restoration has become a central objective in conservation planning. Evaluating landscape functional connectivity and mapping habitat networks are key steps for implementing effective actions, but both remain challenging. Habitat suitability models (HSM) and spatial graphs provide conservation managers with useful information for landscape planning. To tackle their respective drawbacks, we proposed to combine HSM and spatial graphs in a four-step methodological framework: (i) collect and prepare input data; (ii) model habitat suitability using MaxEnt to map the species' habitat suitability index (HSI); (iii) transform the HSI map into spatial graph inputs using GIS; and, (iv) perform spatial graph connectivity analysis using Graphab. The outputs of this species-specific and quantitative approach were maps of the species' habitat network. Habitat patches and dispersal linkages were ranked according to their importance for overall habitat availability and landscape connectivity. This prioritization identified locations where conservation biologists and landscape planners should focus conservation and restoration efforts. This framework is illustrated here with a case study on the woodlark (Lullula arborea) - a bird species - in a French Mediterranean area, and the method's limitations and alternatives are discussed. The quantitative-based graphical outputs of the framework can valuably support decision-making for landscape planning, complement local expert opinion, and encourage appropriate stakeholders to cooperate at regional scale.

[Departement_IRSTEA]EAUX [TR1_IRSTEA]ARCEAU; International audience; This paper presents a comparison of two water transfer schemes implemented in land surface models: a three-layer bulk reservoir model based on the force-restore scheme (FR) and a multilayer soil diffusion scheme (DIF) relying on explicit mass-diffusive equations and a root profile. The performances of each model at simulating evapotranspiration (ET) over a 14-yr Mediterranean crop succession are compared when the standard pedotransfer estimates versus the in situ values of the soil parameters are used. The Interactions between Soil, Biosphere, and Atmosphere (ISBA) generic land surface model is employed. When the pedotransfer estimates of the soil parameters are used, the best performance scores are obtained with DIF. DIF provides more accurate simulations of soil evaporation and gravitational drainage. It is less sensitive to errors in the soil parameters compared to FR, which is strongly driven by the soil moisture at field capacity. When the in situ soil parameters are used, the performance of the FR simulations surpasses those of DIF. The use of the proper maximum available water content for the plant removes the bias in ET and soil moisture over the crop cycle with FR, while soil water stress is simulated too early and the transpiration is underestimated with DIF. Increasing the values of the root extinction coefficient and the proportion of homogeneous root distribution slightly improves the DIF performance scores. Spatiotemporal uncertainties in the soil parameters generate smaller uncertainties in ET simulated with DIF compared to FR, which highlights the robustness of DIF for large-scale applications.

National audience; Two complementary technical approaches are used worldwide to guide the definition of e-flows, at the scale of stream reaches and/or stream catchments. Hydrological approaches are based on the description of the alteration of many components of the flow regime; they rely on the (difficult) identification of relationships between flow alteration and biological alteration. Hydraulic-habitat approaches essentially deal with low to medium flow rates. They combine hydraulic models of reaches with biological models in order to translate some hydrological changes into habitat changes for aquatic organisms. They sometimes provided convincing predictions of the biological effects of low flow changes. These two approaches do not directly provide e-flow values. Here, we formalize a technical framework for defining e-flows, based on the comparison of management scenarios and an improved combination of hydrological and habitat approaches. Four steps are involved: (1) the description of the natural and current hydrological contexts, current water uses and management scenarios; (2) the description of the ecological context; (3) the identification of appropriate metrics (based on hydrology or habitat) to describe the effects of scenarios (changes in water uses and ecological effects); (4) the comparison of scenarios. Applying this framework requires expertise, well defined objectives shared by stakeholders and appropriate monitoring of e-flow implementation.; Deux types d’approches techniques complémentaires sont utilisées pour guider l’établissement des débits écologiques, à l’échelle des tronçons de cours d’eau (ex. : débits réservés) comme à l’échelle de bassins versants (ex. : débits objectifs d’étiage). Les approches « hydrologiques » visent à quantifier les altérations de multiples caractéristiques du régime hydrologique et reposent sur l’identification (délicate) de relations empiriques entre altérations hydrologiques et biologiques. Les approches « habitat hydraulique », ciblées sur les débits bas à moyens, couplent des modèles hydrauliques et des modèles biologiques pour traduire certaines modifications hydrologiques en modification de qualité de l’habitat hydraulique pour les organismes. Elles ont parfois apporté des prédictions convaincantes des effets biologiques des modifications de débits d’étiage. Ces deux approches techniques ne fournissent pas directement de valeurs de débits écologiques. Nous formalisons ici une démarche technique de définition des débits écologiques, basée sur la comparaison de scénarios de gestion et une meilleure combinaison des deux approches. La démarche comprend quatre étapes : (1) la description du contexte hydrologique naturalisé et actuel, des usages actuels et des scénarios de gestion envisagés (2) la description du contexte écologique au sens large, (3) l’identification des métriques pertinentes (hydrologiques et/ou habitats et/ou autres) pour décrire les effets des scénarios (modifications des usages, effets sur le milieu) et (4) la comparaison des scénarios. Cette démarche ne se passe pas d’expertise et doit s’accompagner d’une définition des objectifs partagée par les acteurs ainsi que de retours d’expérience, aspects non détaillés ici.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; This paper explains the spatial variation of the fire metrics throughout SE France which was divided into three regions, each characterized by environmental and socio-economic trends. The most deleterious causes were identified as well as their evolution throughout the year. Using the regional fire database Prométhée, which has gathered information on wildfires in SE France since 1973, different fire metrics such as occurrence, burned area have been investigated in the study area. A general trend was identified in SE France showing that most fires occurred and had the highest impact, in terms of burned area, in summer. When the fire causes were known (only 33.7% of the total ignitions), undetermined arson and negligence during professional work were the most frequently involved. However, because of the interactions between region, season, and cause, the fire metrics could differ from this trend, varying spatially and seasonally according to their cause. Fires due to deliberate causes (especially undetermined arson) were concentrated and impacted mainly region 3 in summer, usually presenting a large mean burned area. In contrast, unintentional fires due to forestry and agricultural works were gathered and had a higher impact mainly in region 1 in winter, and fires due to private work, smaller in size, presented the same pattern but occurred mainly in spring in region 3. This pattern was mainly due to the seasonality of these works. The spatioseasonal variation of natural (lightning) and accidental fires (especially due to power lines and garbage dumps) were mainly driven by climate conditions (regarding lightning and power lines) and/or population density (regarding garbage dumps). When fires smaller than 1ha were removed from the analyses, results could differ regarding the region or season of maximum occurrence and/or mean burned area for fires due to lightning, professional works and negligence during leisure activities. Locating the hotspots of fire occurrence for the main causes will help to improve fire prevention in better allocating law-enforcement and educational measures.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; The application of the GEMAPI ("Management of aquatic lands and flood prevention") skill in France calls to solutions aiming at reconciling flood prevention and integrated management of aquatic lands. Nature-based solutions, based on healthy, resilient, functional and diversified ecosystems for answering the effects of global change, such as climate change and increase of natural risks, shall be eligible for this purpose. These kinds of solution based on the use of eco- and bio-engineering structures, complementary to civil engineering ones, should allow better preventing floods while restoring lands, with an integrated approach at the catchment scale. However, the evaluation of the efficiency of this kind of solutions, in particular on flood prevention, remains a major challenge to which scientists try to answer, through an interdisciplinary approach seeking to assess their ecological and security-based benefits in the framework of the GEMAPI law.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; Suffusion, a particular case of internal erosion in soils, is a particle-scale mechanism involving the selective erosion of fine particles within the matrix of coarse particles under the effect of water seepage. Modifications in the micro-structure as a consequence of the loss of a fine fraction may affect both the hydraulic and the mechanical properties of the soil. Thus leading, in some cases, to drastic consequences. In this study, a discrete numerical model methodology is introduced to investigate the initiation and development of suffusion as well as to analyse its effects on the soil mechanical properties. For that purpose, an original numerical extraction procedure was developed allowing us to mimic the suffusion process by taking into account both the micro-structure of the granular packing and the hydraulic loading in the suffusion development. Such a procedure is based on a one-way fluid-solid coupling where the interstitial flow is solved with a finite volume approach defined at the pore scale. Numerical soil samples subjected to different hydraulic gradients show that depending on the amount and the role of eroded particles in the granular assembly, the eroded medium either shows negligible deformations during erosion but then collapses suddenly once sheared or it deforms significantly during erosion and recovers part of its strength once subjected to shear forces. A non-linear non-monotonic relation between the eroded mass and the mechanical properties of the soil was found.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; Management of aquatic environments and flood prevention are not always compatible, especially when dealing with the complex issue of vegetation on flood protection works, such as dikes. The integration of GEMAPI with dykes must then be assessed on a case-by-case basis, depending on the condition of the structures and the protection issues. This article proposes some ways to reconcile civil engineering and ecological engineering, with an exemplary case study of taking into account aspects of GEMA (management of aquatic environments) and PI (protection of floods) on the dikes of the Leysse in Chambéry.; Gestion des milieux aquatiques et prévention des inondations ne sont pas toujours compatibles, notamment quand on aborde la question complexe de la végétation sur les ouvrages de protection des crues, tels que les digues. L’intégration de la GEMAPI à des linéaires de digues doit alors être évaluée au cas par cas, en fonction de l’état des ouvrages et des enjeux de protection. Cet article propose quelques pistes pour concilier génie civil et génie écologique, avec un cas d’étude exemplaire de prise en compte des aspects GEMA (gestion des milieux aquatiques) et PI (protection des inondations) sur les digues de la Leysse à Chambéry.

Invasion of non-native species is considered a major threat to global biodiversity. Here we present a comprehensive overview of the occurrence, richness and biomass contribution of non-native fish species in 1943 standing water bodies from 14 countries of the Western Palearctic, based on standardised fish catches by multi-mesh gillnetting. We expected strong geographical gradients to emerge in the occurrence of non-natives. We further hypothesised that the contribution by non-natives to the local fish community biomass was correlated with local richness and the trophic level of native and non-native species. Non-native fish species occurred in 304 of 1943 water bodies (16%). If the average number of occupied water bodies per country was weighted by number of water bodies per country, the grand mean occurrence of non-natives in Western Palearctic water bodies was 10%. Exotic (non-native to the Palearctic) and translocated (non-native only to parts of the Palearctic) species were found in 164 (8.4%) or 235 (12.1%) of the water bodies, respectively. The occurrence and local richness of non-native fish species increased with temperature, precipitation and lake area and were substantially higher in reservoirs than in natural lakes. High local biomass contributions of non-native species were strongly correlated with low richness of native species and high richness of non-native species, whereas the trophic level of the fish species had only a weak effect. Single non-native species rarely dominated community biomass, but high biomass contributions and thus strong community and ecosystem impacts can be expected if several non-native species accumulate in a water body. Fil: Trochine, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Limnología; Argentina Fil: Brucet, Sandra. University of Vic; España. Catalan Institution for Research and Advanced Studies; España. Institució Catalana de Recerca i Estudis Avancats; España Fil: Argillier, Christine. Aix En Provence; Francia Fil: Arranz, Ignasi. University of Vic; España Fil: Beklioglu, Meryem. Middle East Technical University; Turquía Fil: Benejam, Lluís. University of Vic; España Fil: Ferreira, Teresa. Universidade de Lisboa; Portugal Fil: Hesthagen, Trygve. Norwegian Institute for Nature Reasearch; Noruega Fil: Holmgren, Kerstin. Swedish University of Agricultural Sciences; Suecia Fil: Jeppesen, Erik. Sino-danish Centre For Education And Research; China. University Aarhus; Dinamarca Fil: Kelly, Fiona. Inland Fisheries Ireland; Irlanda Fil: Krause, Teet. Estonian University of Life Sciences; Estonia Fil: Rask, Martti. Natural Resources Institute Finland; Finlandia Fil: Volta, Pietro. Consiglio Nazionale delle Ricerche; Italia Fil: Winfield, Ian J.. Lancaster Environment Centre; Reino Unido Fil: Mehner, Thomas. Leibniz - Institute of Freshwater Ecology and Inland Fisheries; Alemania

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Lake biological parameters show important spatio-temporal heterogeneities. This is why explaining the spatial patchiness of phytoplankton abundance has been a recurrent ecological issue and is an essential prerequisite for objectively assessing, protecting and restoring freshwater ecosystems. The drivers of these heterogeneities can be identified by modelling their dynamics. This approach is useful for theoretical and applied limnology. In this study, a 3D hydrodynamic model of LakeGeneva (France/Switzerland) was created. It is based on the Delft3D suite software and includes the main tributary (Rhône River) and two-dimensional high-resolution meteorological forcing. It provides 3D maps of water temperature and current velocities with a 1 h time step on a 1 km horizontal grid size and with a vertical resolution of 1 m near the surface to 7 m at the bottom of the lake. The dynamics and the drivers of phytoplankton heterogeneities were assessed by combining the outputs of the model and chlorophyll-a concentration (Chl-a) data from MERIS satellite images between 2008 and 2012. Results highlight physical mechanisms responsible for the occurrence of seasonal hot-spots in phytoplankton abundance in the lake. At the beginning of spring, Chl-a heterogeneities are usually caused by an earlier onset of phytoplankton growth in the shallowest and more sheltered areas; spatial differences in the timing of phytoplankton growth can be explained by spatial variability in thermal stratification dynamics. In summer, transient and locally higher phytoplankton abundances are observed in relation to the impact of basin-scale upwelling.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Widespread tree mortality associated with drought has been observed on all forested continents and global change is expected to exacerbate vegetation vulnerability. Forest mortality has implications for future biosphere–atmosphere interactions of carbon, water and energy balance, and is poorly represented in dynamic vegetation models. Reducing uncertainty requires improved mortality projections founded on robust physiological processes. However, the proposed mechanisms of drought-induced mortality, including hydraulic failure and carbon starvation, are unresolved. A growing number of empirical studies have investigated these mechanisms, but data have not been consistently analysed across species and biomes using a standardized physiological framework. Here, we show that xylem hydraulic failure was ubiquitous across multiple tree taxa at drought-induced mortality. All species assessed had 60% or higher loss of xylem hydraulic conductivity, consistent with proposed theoretical and modelled survival thresholds. We found diverse responses in non-structural carbohydrate reserves at mortality, indicating that evidence supporting carbon starvation was not universal. Reduced non-structural carbohydrates were more common for gymnosperms than angiosperms, associated with xylem hydraulic vulnerability, and may have a role in reducing hydraulic function. Our finding that hydraulic failure at drought-induced mortality was persistent across species indicates that substantial improvement in vegetation modelling can be achieved using thresholds in hydraulic function

[Departement_IRSTEA]Eaux; International audience; The Pyrenean desman, a threatened, semiaquatic mammal, is considered a specialist predator feeding on aquatic benthic invertebrates. This categorization comes from visual identification of prey in scat or gut contents, often based on a limited number of samples and locations. We combined diet analyses using next-generation sequencing methods with an extensive survey to explore the summer diet of Pyrenean desmans across the French Pyrenees. This study thus provides an unprecedented level of detail on the trophic ecology of Pyrenean desmans. Our results revealed a diverse diet containing a high proportion of rare prey and substantial consumption of terrestrial prey, which suggests a more generalist diet than previously understood. Three diet groups were identified, with significant differences in prey composition. These differences were not related to geographic location, but rather to local environmental variables. The spatial variation in diet was likely induced by local abiotic parameters that affect prey availability or use of foraging habitats.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Current decreasing precipitation and increasing temperatures promote the likelihood of extreme drought events and may alter the recruitment capacities of tree species. Spanish black pine (Pinus nigra ssp. salzmannii) initial recruitment is being one of the most affected pine species by changing conditions with alterations in the future species distribution. In this context, a cross-exchange experiment was implemented using an outdoor nursery located in a warmer and drier location for testing different Spanish Black pine seeds and soil provenance combinations in relation to early recruitment and initial seedling growth. Soil and seeds were collected at a high (HA, 1641 m.a.s.l.) and low (LA, 1099 m.a.s.l.) altitude in Cuenca Mountains (Spain). Then, a cross-sown experiment using HA and LA soils and seeds was set up in an outdoor nursery, which is located in Albacete (704 m.a.s.l.). Soil quality, seedling emergence, seedling survival, initial seedling growth and total seedling dry mass were measured after one year. We found higher seed emergence and seedling survival by combining LA soil with LA seeds or HA soil with HA seeds. Seedlings from LA seeds with both soil origins and seedlings from HA seeds with LA soils allocated more biomass to roots than seedlings from HA sites growing in HA soils under drier and warmer conditions. These results support the idea that autochtonous provenances have the potential to adapt to changing climatic conditions in their habitats.

[Departement_IRSTEA]Territoires [ADD1_IRSTEA]Dynamiques spatiales d'anthropisation [ADD2_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; Context Land use and land cover (LULC) change is a major part of environmental change. Understanding its long-term causes is a major issue in landscape ecology.Objectives Our aim was to characterise LULC transitions since 1860 and assess the respective and changing effects of biophysical and socioeconomic drivers on forest, arable land and pasture in 1860, 1958 and 2010, and of biophysical, socioeconomic and distance from pre-existing forest on forest recovery for the two time intervals.Methods We assessed LULC transitions by superimposing 1860, 1958 and 2010 LULCs using a regular grid of 1 9 1 km points, in a French Mediterranean landscape (195,413 ha). We tested the effects of drivers using logistic regressions, and quantified pure and joint effects by deviance partitioning.Results Over the whole period, the three main LULCs were spatially structured according to land accessibility and soil productivity. LULC was driven more by socioeconomic than biophysical drivers in 1860, but the pattern was reversed in 2010. A widespread forest recovery mainly occurred on steeper slopes, far from houses and close to pre-existing forest, due to traditional practice abandonment. Forest recovery was better explained by biophysical than by socioeconomic drivers and was more dependent on distance from pre-existing forest between 1958 and 2010.Conclusions: Our results showed a shift in drivers of LULC and forest recovery over the last 150 years. Contrary to temperate regions, the set-aside of agricultural practices on difficult land has strengthened the link between biophysical drivers and LULC distribution over the last

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Hydrosystèmes et risques naturels [ADD2_IRSTEA]Dynamique et fonctionnement des écosystèmes [ADD2_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; The analysis of concentration-discharge (C-Q) relationships provides useful information on the processes controlling the mobilization and delivery of chemical elements into streams as well as biogeochemical transformations in river networks. Previous metrics developed to characterize export regimes seldom considered the possibility for the C response to Q dynamics to differ between short-term Q variations during storm events and seasonal Q variations during baseflow periods. Here, we present the “C-Qquick-slow” model, which considers the possibility for C-Q relationships to vary across temporal scales. This model was applied in 219 French catchments with various sizes (11–2500 km2), land use and hydrological contexts. We evidenced contrasting export regimes for nitrate (NO3 −), total phosphorus (TP) and soluble reactive phosphorus (SRP), and surprisingly consistent C-Q patterns at the seasonal scale for each parameter. For instance, NO3 −-Q relationships were positive at the seasonal scale in 75% cases and relationships during storms showed either a dilution pattern (24% cases), a non-significant pattern (50%), or a mobilization pattern (12%). TP and SRP relationships with Q at the seasonal scale were almostsystematically negative (95%), and patterns during storm events were in most cases mobilization for TP (77%) or non-significant for SRP (69%). We linked the different C-Q relationships with catchment descriptors and found that indicators of diffuse source loading determined NO3 − seasonal amplitudes, and hydrological drivers could explain the behavior during storms. By contrast, point sources determined P seasonal amplitudes, and diffuse sources controlled P dynamics during storms. The C-Qquick-slow model has the potential to improve nutrient loadestimations because of the good predictability of appropriate C-Q archetypes and the possibility to interpolate low frequency concentration data to a daily frequency

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; 1. Significant pine mortality has been observed in mountainous areas with a Mediterranean climate over recent decades, impacting ecosystem function and economic management of these forests. Despite this, few studies have examined how forest management can interact with disturbances to influence pine mortality.2. We used process-based models to quantify the spatial distribution of a typical vegetation assemblage of Corsican pine forests, and evaluate how different landscape patterns and fire regimes (i.e. burned area and fire intensity) affect plant communities. For all 18 scenarios examined, fire return interval was fixed at 100 ± 70 years that corresponded to the mean ± standard deviation reconstructed for the last 6000 years in this ecosystem.3. Results indicate that the most species diverse Corsican pine ecosystems over the past 6000 years of history are best explained by a high fire frequency of small fires that cover a large area in total in a climate comparable with today. An increase in mean annual temperature of 1 or 2 °C is sufficient to decrease the diversity of the ecosystem. In addition, a mosaic landscape pattern is correlated with high plant species diversity, and is associated with medium to low fire intensity, and small burned areas (3 to 5% of the landscape).4. Synthesis and applications: The diversity of the Corsican pine forest as recorded in the past 6000 years is likely explained by frequent fires of medium to low intensity. Thus, we encourage pine forest managementin Corsica (and in the Mediterranean mountain belt) to use frequent disturbances, such as clear felling, to promote a mosaic landscape that facilitates species diversity and presence of Corsican black pine.