Big Cities, Big Impacts? A spatial analysis of 3,335 ecological offsets in France since 2012

This paper assesses the French policy of mitigation hierarchy, with the aim of no net loss of biodiversity, by studying the geographical aspects of the application of the concept of ecological offsets in equivalence between losses and gains using spatialized data. We seek to know whether the dynamics of urban and interurban development (notably built-up and transport infrastructures) lead to a spatially integrated implementation of biodiversity offsets taking into account local characteristics and areas under pressure from land artificialization. Our main finding reveals that the majority of ecological offsets are generated by projects related to transport infrastructures (38%) and urban planning and construction projects (23%). However, if there are fewer, the ecological offsets of projects such as waste storage or energy development are mostly located in natural preserved areas, revealing a potential risk of non additionnality of offset measures and a risk that the private sector (through ecological offsets) will gradually replace the state in the protection of biodiversity. Our analysis also points out that despite the diversity of projects, habitats and protected species across France, there is a typical spatial layout profile of ecological offsets, pleading for a "one size fits all" offsetting in the French policy context of tenuous regulators' availability in time and competence level due to weakness of refresh training and downsizing of public services in the environment. This last result argues for a stronger control from environmental agencies between two tremendously tricky concepts of offsetting, the equivalence valuation methods and the adjustments coefficients (time delay and ecological risk), to drive ecological offsetting future decisions at local but above all regional- and national-level planning documents.

Optimizing detectability of the endangered fan mussel using eDNA and ddPCR

Spatial and temporal monitoring of species threatened with extinction is of critical importance for conservation and ecosystem management. In the Mediterranean coast, the fan mussel (Pinna nobilis) is listed as critically endangered after suffering from a mass mortality event since 2016, leading to 100% mortality in most marine populations. Conventional monitoring for this macroinvertebrate is done using scuba, which is challenging in dense meadows or with low visibility. Here we developed an environmental DNA assay targeting the fan mussel and assessed the influence of several environmental parameters on the species detectability in situ. We developed and tested an eDNA molecular marker and collected 48 water samples in two sites at the Thau lagoon (France) with distinct fan mussel density, depths and during two seasons (summer and autumn). Our marker can amplify fan mussel DNA but lacks specificity since it also amplifies a conspecific species (Pinna rudis). We successfully amplified fan mussel DNA from in situ samples with 46 positive samples (out of 48) using ddPCR, although the DNA concentrations measured were low over almost all samples. Deeper sampling depth slightly increased DNA concentrations, but no seasonal effect was found. We highlight a putative spawning event on a single summer day with much higher DNA concentration compared to all other samples. We present an eDNA molecular assay able to detect the endangered fan mussel and provide guidelines to optimize the sampling protocol to maximize detectability. Effective and non-invasive monitoring tools for endangered species are promising to monitor remaining populations and have the potential of ecological restoration or habitat recolonization following a mass mortality event.

Offset sizing tools: A review of practices used in the field and their operationality

The mitigation hierarchy (avoid, minimize, restore/rehabilitate and, lastly, offset or compensate) is one of the key regulatory mechanisms that exists to include biodiversity protection in land-use planning. Implementing the mitigation hierarchy requires the use by practitioners (developers, environmental consultants and government agencies) of operational mitigation assessment methods, or offset sizing methods. This study focused on one aspect of operationality: usefulness. Through an approach based on ergonomics, we analysed practices used in the field in order to concretely identify in what way an offset sizing method is useful to developers, consultants and public officials. The findings showed that sizing offset measures is a collective process involving all these stakeholders, that these practitioners vary significantly in their level of knowledge about ecology and their degree of expertise in the mitigation hierarchy, and that each method is not equally useful for each type of stakeholder. Our conclusion is that to improve operationality, these methods must be adapted into tools that are relevant to the specific user and context.

Ecological equivalence assessment: The potential of genetic tools, remote sensing and metapopulation models to better apply the mitigation hierarchy

Within the framework of the mitigation hierarchy, biodiversity offsetting is the main tool promoted to reach No Net Loss. One of the determining factors of offsetting success is the evaluation of ecological equivalence. Various equivalence assessment methods (EAMs) have been developed to provide a framework to evaluate the balance between expected biodiversity losses and gains. In the context of achieving No Net Loss, EAMs must address challenges of Operationality, Currency, Uncertainty, Spatial scale and Time frame. In this study, we investigated the way the most widely used EAMs address these challenges, positing that certain tools from ecological science could limit the trade-offs between these challenges and improve the ecological assessment process. To this end, we analysed the risks and benefits associated with the inclusion of genetic tools (landscape genetics and eDNA), remote sensing and metapopulation models in selected EAMs. Our results revealed trade-offs between these five challenges, in particular between Operationality and Currency. The EAMs varied strongly in these two aspects, depending on the general assessment approach and the biodiversity component they focus on. To a lesser degree, Time frame and Spatial scale also differed between the methods. We identified that the integration of the different tools differs among them, being easier for remote sensing and metapopulation models than for the genetic tools. Nevertheless, the integration resulted in benefits compared to the current use of the methods - benefits that included improving the objectivation of the assessment and the automatization potential. The tools also show potential for automatization, which could have major benefits for operationality. In terms of risks, the integration of these tools increases the technical complexity of the methods, requiring new skills, and would change the overall approach of the ecological assessment.

The inclusion of biodiversity in environmental impact assessment: Policy-related progress limited by gaps and semantic confusion

Natural habitat loss and fragmentation, as a result of development projects, are major causes of biodiversity erosion. Environmental impact assessment (EIA) is the most commonly used site-specific planning tool that takes into account the effects of development projects on biodiversity by integrating potential impacts into the mitigation hierarchy of avoidance, reduction, and offset measures. However, the extent to which EIA fully address the identification of impacts and conservation stakes associated with biodiversity loss has been criticized in recent work. In this paper we examine the extent to which biodiversity criteria have been integrated into 42 EIA from 2006 to 2016 for small development projects in the Montpellier Metropolitan territory in southern France. This study system allowed us to question how EIA integrates biodiversity impacts on a scale relevant to land-use planning. We examine how biodiversity inclusion has changed over time in relation to new policy for EIA and how the mitigation hierarchy is implemented in practice and in comparison with national guidelines. We demonstrate that the inclusion of biodiversity features into EIA has increased significantly in relation to policy change. Several weaknesses nevertheless persist, including the continued absence of substitution solution assessment, a correct analysis of cumulative impacts, the evaluation of impacts on common species, the inclusion of an ecological network scale, and the lack of monitoring and evaluation measures. We also show that measures for mitigation hierarchy are primarily associated with the reduction of impacts rather than their avoidance, and avoidance and offset measures are often misleadingly proposed in EIA. There is in fact marked semantic confusion between avoidance, reduction and offset measures that may impair stakeholders' understanding. All in all, reconsideration of stakeholders routine practices associated with a more strategic approach towards impact anticipation and avoidance at a land-use planning scale is now necessary for the mitigation hierarchy to become a clear and practical hierarchy for "no net loss" objectives based on conservation priorities.

Improving marine biodiversity offsetting: A proposed methodology for better assessing losses and gains

Although the limitations of implementing the mitigation hierarchy have been widely discussed in scientific literature, these studies have drawn mainly on feedback concerning terrestrial ecosystems. In the case of development projects in marine and coastal environments, certain issues must be tackled to improve existing practice. This article focuses on the methodologies used to assess both the ecological losses resulting from a development project and the ecological gains generated by an offset measure. The originality of this article is to propose a standardized, operational approach regardless of the development project and the ecosystem impacted that (i) enhances avoidance and reduction efforts and (ii) assesses biodiversity offset needs based on data available in Environmental Impact Assessments (EIAs). The proposed hybrid method combines a multi-criteria analysis of the state of the environment, inspired by the Unified Mitigation Assessment Method (UMAM), and a more accurate assessment at indicator level inspired by Habitat Equivalency Analysis (HEA). The steps of the method, from the selection of biophysical indicators to offset sizing, are described and are then applied to two EIA case studies: one related to a port extension and the other to an offshore wind farm.