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

La dimension culturelle des évaluations de zones humides d'eau douce : enseignements issus de l'application en France des méthodes d’évaluation rapide des zones humides développées aux États-Unis

International audienceGiven the recent strengthening of wetland restoration and protection policies in France, there is need to develop rapid assessment methods that provide a cost-effective way to assess losses and gains of wetland functions. Such methods have been developed in the US and we tested six of them on a selection of contrasting wetlands in the Isère watershed. We found that while the methods could discriminate sites, they did not always give consistent rankings, thereby revealing the different assumptions they explicitly or implicitly incorporate. The US assessment methods commonly use notions of "old-growth" or "pristine" to define the benchmark conditions against which to assess wetlands. Any reference-based assessment developed in the US would need adaptation to work in the French context. This could be quite straightforward for the evaluation of hydrologic variables as scoring appears to be consistent with the best professional judgment of hydrologic condition made by a panel of French local experts. Approaches to rating vegetation condition and landscape context, however, would require substantial reworking to reflect a novel view of reference standard. Reference standard in the European context must include acknowledgement that many of the best condition and biologically important wetland types in France are the product of intensive, centuries-long management (mowing, grazing, etc.). They must also explicitly incorporate the recent trend in ecological assessment to focus particularly on the wetland’s role in landscape-level connectivity. These context-specific, socio-cultural dimensions must be acknowledged and adjusted for when adapting or developing wetland assessment methods in new cultural contexts