Environmental mitigation hierarchy and biodiversity offsets revisited through habitat connectivity modelling.

Biodiversity loss is accelerating because of unceasing human activity and land clearing for development projects (urbanisation, transport infrastructure, mining and quarrying …). Environmental policy-makers and managers in different countries worldwide have proposed the mitigation hierarchy to ensure the goal of "no net loss (NNL) of biodiversity" and have included this principle in environmental impact assessment processes. However, spatial configuration is hardly ever taken into account in the mitigation hierarchy even though it would greatly benefit from recent developments in habitat connectivity modelling incorporating landscape graphs. Meanwhile, national, European and international commitments have been made to maintain and restore the connectivity of natural habitats to face habitat loss and fragmentation. Our objective is to revisit the mitigation hierarchy and to suggest a methodological framework for evaluating the environmental impact of development projects, which includes a landscape connectivity perspective. We advocate the use of the landscape connectivity metric equivalent connectivity (EC), which is based on the original concept of "amount of reachable habitat". We also refine the three main levels of the mitigation hierarchy (impact avoidance, reduction and offset) by integrating a landscape connectivity aspect. We applied this landscape connectivity framework to a simple, virtual habitat network composed of 14 patches of varying sizes. The mitigation hierarchy was addressed through graph theory and EC and several scenarios of impact avoidance, reduction and compensation were tested. We present the benefits of a habitat connectivity framework for the mitigation hierarchy, provide practical recommendations to implement this framework and show its use in real case studies that had previously been restricted to one or two steps of the mitigation hierarchy. We insist on the benefits of a habitat connectivity framework for the mitigation hierarchy and for ecological equivalence assessment. In particular, we demonstrate why it is risky to use a standard offset ratio (the ratio between the amount of area negatively impacted and the compensation area) without performing a connectivity analysis that includes the landscape surrounding the zone impacted by the project. We also discuss the limitations of the framework and suggest potential improvements. Lastly, we raise concerns about the need to rethink the strategy for biodiversity protection. Given that wild areas and semi-natural habitats are becoming scarcer, in particular in industrialised countries, we are convinced that the real challenge is to quickly reconsider the current vision of "developing first, then assessing the ecological damage", and instead urgently adopt an upstream protection strategy that would identify and protect the land that must not be lost if we wish to maintain viable species populations and ecological corridors allowing them the mobility necessary to their survival.

Ecological Equivalence Assessment Methods: What Trade-Offs between Operationality, Scientific Basis and Comprehensiveness?

In many countries, biodiversity compensation is required to counterbalance negative impacts of development projects on biodiversity by carrying out ecological measures, called offset when the goal is to reach "no net loss" of biodiversity. One main issue is to ensure that offset gains are equivalent to impact-related losses. Ecological equivalence is assessed with ecological equivalence assessment methods taking into account a range of key considerations that we summarized as ecological, spatial, temporal, and uncertainty. When equivalence assessment methods take into account all considerations, we call them "comprehensive". Equivalence assessment methods should also aim to be science-based and operational, which is challenging. Many equivalence assessment methods have been developed worldwide but none is fully satisfying. In the present study, we examine 13 equivalence assessment methods in order to identify (i) their general structure and (ii) the synergies and trade-offs between equivalence assessment methods characteristics related to operationality, scientific-basis and comprehensiveness (called "challenges" in his paper). We evaluate each equivalence assessment methods on the basis of 12 criteria describing the level of achievement of each challenge. We observe that all equivalence assessment methods share a general structure, with possible improvements in the choice of target biodiversity, the indicators used, the integration of landscape context and the multipliers reflecting time lags and uncertainties. We show that no equivalence assessment methods combines all challenges perfectly. There are trade-offs between and within the challenges: operationality tends to be favored while scientific basis are integrated heterogeneously in equivalence assessment methods development. One way of improving the challenges combination would be the use of offset dedicated data-bases providing scientific feedbacks on previous offset measures.

Relative contribution of soil, management and traits to co-variations of multiple ecosystem properties in grasslands.

Ecological intensification promotes the better use of ecosystem functioning for agricultural production and as a provider of additional regulation and cultural services. We investigated the mechanisms underpinning potential ecological intensification of livestock production in the Vercors mountains (France). We quantified the variations in seven ecosystem properties associated with key ecosystem services: above-ground biomass production at first harvest, fodder digestibility, plant species richness, soil organic matter content, soil carbon content, total microbial biomass and soil bacteria:fungi ratio across 39 grassland plots representing varying management types and intensity. Our analyses confirmed joint effects of management, traits and soil abiotic parameters on variations in ecosystem properties, with the combination of management and traits being most influential. The variations explained by traits were consistent with the leaf economics spectrum model and its implications for ecosystem functioning. The observed independence between ecosystem properties relevant to production (forage biomass, digestibility and nutrient turnover) on the one hand and soil stocks (organic matter, carbon and microbial stocks) on the other hand suggests that an intensification of fodder production might be compatible with the preservation of the soil capital. We highlight that appropriate choices regarding various practices, such as the first date of grazing or mowing being dependent on soil moisture, have important consequences on a number of ecosystem properties relevant for ecosystem services and may influence biodiversity patterns. Such avenues for ecological intensification should be considered as part of further landscape- and farm-scale analyses of the relationships between farm functioning and ecosystem services.

A global meta-analysis of the relative extent of intraspecific trait variation in plant communities.

Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.

The Cultural Dimensions of Freshwater Wetland Assessments: Lessons Learned from the Application of US Rapid Assessment Methods in France.

Given 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.