Les enjeux de l’équivalence écologique pour la conception et le dimensionnement de mesures compensatoires d’impacts sur la biodiversité et les milieux naturels,

L’évolution du contexte réglementaire a renforcé l’obligation de compenser " en nature " les impacts sur la biodiversité qui n’ont pas pu être évités ou réduits. Dans ce contexte, l’évaluation de l’équivalence entre les pertes causées par ces impacts et les gains de biodiversité attendus des actions de compensation suscite des questions scientifiques et techniques quant aux concepts et connaissances à mobiliser et aux méthodes d’évaluation à développer et mettre en ½uvre. On y trouve en particulier l'identification des éléments de biodiversité à considérer, le développement d’indicateurs appropriés permettant de comparer pertes et gains, la sélection d’un état de référence pour le calcul des pertes et gains, et la prise en compte des dynamiques écologiques et des incertitudes dans l’évaluation du devenir des sites de compensation. Par ces questions, l'équivalence écologique donne un cadre de raisonnement explicite à la conception et au dimensionnement de la compensation qui est appropriable par chacun des acteurs concernés. / Since 2007 France has seen a radical strengthening of its legislation concerning the mitigation of development impacts on biodiversity and ecosystems. Under pressure from the European Union and as an outcome of a national consultative process called the “Grenelle de l’Environnement”, the scope of the mitigation hierarchy of avoiding, reducing and offsetting impacts of plans, programs and projects has been expanded. It now includes stronger requirements in terms of monitoring and effective implementation. These changes – which have strong financial and legal implications for developers - have revealed the lack of technical guidelines for designing and sizing offsets. Assessing the ecological equivalence between losses caused by impacts and the gains expected from offset actions raises scientific and technical issues that remain unresolved. These include the identification of relevant components of biodiversity, the development of appropriate indicators, the identification of reference states and the incorporation of ecological dynamics and uncertainties into offset design and sizing

Discrete-time controlled markov processes with average cost criterion: a survey

This work is a survey of the average cost control problem for discrete-time Markov processes. The authors have attempted to put together a comprehensive account of the considerable research on this problem over the past three decades. The exposition ranges from finite to Borel state and action spaces and includes a variety of methodologies to find and characterize optimal policies. The authors have included a brief historical perspective of the research efforts in this area and have compiled a substantial yet not exhaustive bibliography. The authors have also identified several important questions that are still open to investigation

Un cadre méthodologique pour évaluer l'équivalence entre pertes et gains de biodiversité induits par les projets d'aménagement et leurs mesures compensatoires

In France, the Mitigation hierarchy aims to achieve the "no net loss" (NNL) of biodiversity at the development projects scale. One of the key issues to achieve this goal is to demonstrate the ecological equivalence between the gains associated with offsets and the losses caused by the impacts. Despite regulatory improvements, the French law does not include a method to follow for determining equivalence, and none is unanimously recognized. This leads to heterogeneous practices and difficulty in reaching the NNL. In this context, we have developed a methodological framework for assessing equivalence adapted to the French regulatory and ecological context and combining three challenges: operationality, scientific basis and comprehensiveness. This methodological framework makes it possible 1 / to evaluate the biodiversity found on impacted and compensating sites by taking into account ordinary biodiversity and the one of interest, with a focus on functionalities; 2 / to estimate the value of the indicators after impact and MC, in the short and long term, taking into account associated uncertainties; and 3 / calculating losses and gains leading to a quantitative and transparent equivalence assessment. The use of the methodological framework favors dialogue between actors and also allows monitoring of offsets over time.En France, la séquence « Eviter Réduire Compenser » (ERC) a pour objectif d'atteindre « l'absence de perte nette (APN) » de biodiversité à l'échelle des projets d'aménagement. Un des enjeux clé pour y arriver consiste à démontrer l'équivalence écologique entre les gains associés aux mesures compensatoire (MC) et les pertes occasionnées par les impacts. Malgré les avancées règlementaires, le cadre français n'inclut pas de méthode à suivre pour déterminer l'équivalence et aucune n'est unanimement reconnue. Cela amène à des pratiques hétérogènes et une difficulté d'atteindre l'APN. Dans ce contexte, nous avons développé un cadre méthodologique d'évaluation de l'équivalence adapté au contexte règlementaire et écologique français, répondant à trois défis : opérationnalité, bases scientifiques et exhaustivité. Ce cadre méthodologique permet 1/ d'évaluer la biodiversité des sites impactés et compensatoires en tenant compte de la biodiversité ordinaire et à enjeu en insistant sur les fonctionnalités, 2/ d'estimer la valeur des indicateurs après impact et MC à court et long terme, en prenant en compte les incertitudes associées et 3/ de calculer les pertes et des gains, aboutissant ainsi à une évaluation quantitative et transparente de l'équivalence. L'utilisation du cadre méthodologique favorise la concertation entre acteurs et permet également un suivi des MC dans le temps

New method for rapid assessment of the functional composition of herbaceous plant communities

International audienceWe propose a rapid sampling method to assess the functional composition of herbaceous plant communities without prior knowledge of the floristic composition. To determine the community-level value of traits ('aggregated trait values') for a plant community, a standardized population-centred method exists, but requires substantial manpower and reliable botanical knowledge. We tested an alternative method, the trait transect, using four subalpine pastures in the Beaufortain region (Northern French Alps) selected along a fertility gradient. We applied both methods to measure five commonly used 'soft traits' known to be responsive to soil nutrient availability: plant vegetative and reproductive height, specific leaf area, leaf dry matter and nitrogen contents. We tested whether the variation of these traits along the gradient detected with the population-centred method was also detected with the trait transect. Both methods detected expected trends in the traits in response to the fertility gradient. The trait transect method was as efficient as the population-centred method and is recommended as an appropriate tool for monitoring ecosystem changes in response to environmental conditions and management, especially in species-rich communities

Utilisation du système d'information géographique comme outil de gestion de zones humides d'altitude : le cas du domaine skiable de Val Thorens

Dans quelle mesure l'utilisation d'un système d'information géographique peut-elle aider à la gestion des zones humides de montagne ? Quel est l'intérêt d'un outil de cartographie dans la définition des mesures de gestion et de restauration ? Premiers éléments de réponse et perspectives d'utilisation pour les gestionnaires des zones humides d'altitude du domaine skiable de Val Thorens

Importance and intensity of competition along a fertility gradient and across species

International audienceQuestions: 1. Can the importance and the intensity of competition vary independently along a nutrient gradient? 2. Are these variations species dependent? Location: Sub-alpine pastures of the northern French Alps. Methods: Competition intensity measures how much competition decreases the performances of an organism. Competition importance measures how much competition contributes to affect performance, among other processes (such as environmental stress or disturbance). Competition intensity and importance were measured on three co-occurring species: Festuca rubra, a perennial grass, and two forbs of contrasting basal area, Chaerophyllum hirsutum and Alchemilla xanthochlora. A neighbour removal experiment was performed on Festuca rubra in three sub-alpine grassland communities differing in fertility and on Chaerophyllum hirsutum and Alchemilla xanthochlora in the two more fertile of these communities. The importance of competition was quantified using an index proposed by Brooker et al. (2005). Results: Competition intensity and importance showed different patterns of variation along the fertility gradient for Festuca rubra: competition importance decreased with decreasing fertility whereas competition intensity did not change. The largest forb was the least affected by competition. Our results suggest that the importance of competition for all three species depended on their individual tolerance to low nutrient availability. Conclusions: 1. The distinction between the importance and the intensity of competition is helpful to explain conflicting results obtained on the variations of competition indices along productivity gradients. 2. The choice of a phytometer can affect the conclusions drawn from empirical studies

De la réparation à la restauration. La revégétalisation des pistes de ski à l'Alpe d'Huez

consultable en ligne: URL : http://rga.revues.org/1249International audienceA partir d'une approche sociologique empirique, ce texte propose une analyse de la mise en œuvre de la revégétalisation sur la station de l'Alpe d'Huez depuis les années 1970. Il montre comment la revégétalisation est passée d'un objectif de réparation des cicatrices provoquées par les aménagements à une entreprise plus complexe de restauration. S'il s'agissait au départ de répondre à un objectif technique de lutte contre l'érosion, la revégétalisation a pris rapidement une tournure paysagère (reverdissement) ; elle a ensuite été pensée dans une perspective de restauration des écosystèmes ainsi que de restauration d'un paysage culturel " typique ". Aujourd'hui, gestionnaires de la station, techniciens, agriculteurs et chercheurs impliqués partagent un désir d'autochtonie qui touche dans certains cas à la foklorisation. Loin d'une perspective éthique surplombante, cette étude suggère ainsi comment les caractéristiques physiques du territoire, son histoire et la configuration des acteurs locaux informent largement les arbitrages et les choix techniques qui président à la restauration écologique, ainsi que les débats qui l'entourent. En conclusion, nous discutons de la spécificité de nos résultats et de leur validité pour d'autres stations alpines

Évolution des stocks de carbone en fonction des trajectoires de gestion en zone humide

Ecosystem services (ES) are now taken into account in management schemes and impact studies. Given current climate change, global climate regulation by ecosystem carbon storage is an ES of great concern. This is especially the case for wetland protection and restoration, which as fragile ecosystems are already managed for conservation. We used a state-and-transition model for 24 wetland plots to determine whether such management actions can change their carbon stock. Aboveground biomass of forested wetlands stored twice as much carbon as herbaceous undrained wetlands. Soil organic carbon stock was unchanged across the three studied main states, and was thus independent of their vegetation. This study highlights the importance of the wetland soil carbon pool for global climate regulation, as it represented > 50 % of the total carbon stock for the three studied states, but also the difficulties to manage this complex pool. Also, it points out the advantage of state-and-transition models to follow and/or project management effects on ES. This approach could be used in the context of the mitigation hierarchy for No Net Loss of biodiversity and ecosystem services

Évolution des stocks de carbone en fonction des trajectoires de gestion en zone humide

Ecosystem services (ES) are now taken into account in management schemes and impact studies. Given current climate change, global climate regulation by ecosystem carbon storage is an ES of great concern. This is especially the case for wetland protection and restoration, which as fragile ecosystems are already managed for conservation. We used a state-and-transition model for 24 wetland plots to determine whether such management actions can change their carbon stock. Aboveground biomass of forested wetlands stored twice as much carbon as herbaceous undrained wetlands. Soil organic carbon stock was unchanged across the three studied main states, and was thus independent of their vegetation. This study highlights the importance of the wetland soil carbon pool for global climate regulation, as it represented > 50 % of the total carbon stock for the three studied states, but also the difficulties to manage this complex pool. Also, it points out the advantage of state-and-transition models to follow and/or project management effects on ES. This approach could be used in the context of the mitigation hierarchy for No Net Loss of biodiversity and ecosystem services