Considering habitat connectivity in urban development and the application of the mitigation hierarchy : From project scale to planning

La biodiversité est confrontée à une érosion accélérée et est devenue une préoccupation environnementale mondiale ces dernières décennies. En France, la séquence Éviter–Réduire–Compenser (ERC) est un des outils réglementaires mis en place dans un contexte de destruction et de fragmentation des habitats d’espèces. Elle permet le développement des territoires tout en visant une absence de perte nette de biodiversité. Cependant, malgré les récentes évolutions réglementaires européennes et françaises, le triptyque ERC présente de nombreuses limites et enjeux d’ordre opérationnel. En positionnant nos travaux à l’interface entre recherche et opérationnalité, nous proposons un cadre méthodologique basé sur plusieurs approches de modélisation afin d’améliorer les processus d’évaluation et décisionnels aux différentes étapes d’aménagement, de la planification à l’opérationnel au moment de l’autorisation des projets. Dans une première partie du travail, nous intégrons les enjeux spatio-temporels de la biodiversité à l’ensemble de la séquence ERC, de l’évaluation des impacts potentiels au dimensionnement des mesures écologiques. À partir du cas précis de l’aménagement du Grand Stade de Lyon, nous montrons l’intérêt de combiner les modèles de distribution d’espèces et les graphes paysager pour identifier les réseaux écologiques et poser un cadre de calcul de l’équivalence écologique basé sur le volet fonctionnel de la biodiversité. Intégrer les dimensions spatiales et temporelles permet d’accroitre la connectivité des habitats et améliorer la conception des projets. Nous montrons ensuite qu’organiser la compensation à l’échelle des territoires en les intégrant aux réseaux écologiques améliore davantage les bénéfices et réduit le risque d’échecs des mesures. Notre démarche est présentée dans le contexte périurbain de l’Ouest de Lyon. Enfin, nous démontrons les implications d’une démarche anticipée et planifiée de la séquence ERC dans la planification stratégique des territoires. Pour cela, nous montrons dans le cadre de la Métropole de Toulouse l’intérêt d’étudier conjointement les dynamiques urbaines et écologiques pour mettre en place une stratégie de conservation de la biodiversité à l’horizon 2040 en assurant l’absence de perte nette sur les habitats d’espèces et leur connectivité selon différentes trajectoires d’urbanisation et de ratio de compensation. Cette thèse offre une approche globale pour orienter les décideurs et améliorer la prise en compte des fonctionnalités écologiques à différentes échelles spatiales et temporelles dans l’aménagement des territoires et l’application de la séquence ERC. Ce travail est basé sur des logiciels novateurs et accessibles pour tous les acteurs et constitue une contribution intéressante à l’appui des maitres d’ouvrage qui souhaitent s’assurer de l’absence d'effets significatifs ou irréversibles sur la biodiversité, et des autorités environnementales qui veillent à ce que l’ensemble des enjeux environnementaux soient bien pris en compte dans la conception des projets d’aménagement.Over the past decades, biodiversity erosion has speeded up and become a global environmental concern since. Anthropization has led to. The mitigation hierarchy (avoidance, reduction and offsetting of impacts) is a regulatory tool implemented in a context of habitat destruction and fragmentation, disrupting species’ life cycle. The objective is to achieve “no net loss” of biodiversity following urban development. Although biodiversity conservation regulations have recently better addressed ecosystem functioning, the mitigation hierarchy is still being implemented with little concern for the spatial configuration of ecosystems in the landscape. This thesis hypothesizes that the major difficulties encountered by stakeholders are, in part, methodological and technical. Situating our research at the knowledge-action interface, we propose a methodological framework based on several modeling approaches, to respond to the different scientific and operational challenges. This thesis joins forces with other scientific projects and stakeholders’ networks by exploring complementary axes. To this end, we first integrate spatio-temporal issues of biodiversity into overall mitigation hierarchy application, focusing on potential impacts and dimensioning at “territorial development project” scale through a case study on the new stadium in Lyon (Southern France). Combining species distributions models and spatial graphs improves habitat connectivity and therefore the design of the development projects. Next, we demonstrate the positive impacts on peri-urban habitat connectivity of pooling and anticipating offsets in the suburbs of Lyon. In the last part, we demonstrate the implications of an anticipated and planned approach to the mitigation hierarchy on a planning scale. We consider both ecological connectivity and urban dynamics, in an attempt to minimize the ecological impacts of urban sprawl by avoiding urbanization of areas of highest ecological value and then enhance the application of biodiversity offsetting. This method is tested on projections for the Toulouse conurbation (Southern France) by 2040. Thus, this thesis presents an overall approach that can help to increase habitat connectivity and to improve the design of territorial development projects at different spatial and temporal scales. This methodology is based on freeware available to all practitioners. It will serve planners, designers, and decision-makers needing to ensure that there are no significant or irreversible effects on biodiversity, and environmental authorities making sure that all environmental issues are taken into account in the design of development projects

La prise en compte des fonctionnalités écologiques dans l'aménagement des territoires et l'application de la séquence Éviter-Réduire-Compenser : De l'échelle projet à la planification

Over the past decades, biodiversity erosion has speeded up and become a global environmental concern since. Anthropization has led to. The mitigation hierarchy (avoidance, reduction and offsetting of impacts) is a regulatory tool implemented in a context of habitat destruction and fragmentation, disrupting species’ life cycle. The objective is to achieve “no net loss” of biodiversity following urban development. Although biodiversity conservation regulations have recently better addressed ecosystem functioning, the mitigation hierarchy is still being implemented with little concern for the spatial configuration of ecosystems in the landscape. This thesis hypothesizes that the major difficulties encountered by stakeholders are, in part, methodological and technical. Situating our research at the knowledge-action interface, we propose a methodological framework based on several modeling approaches, to respond to the different scientific and operational challenges. This thesis joins forces with other scientific projects and stakeholders’ networks by exploring complementary axes. To this end, we first integrate spatio-temporal issues of biodiversity into overall mitigation hierarchy application, focusing on potential impacts and dimensioning at “territorial development project” scale through a case study on the new stadium in Lyon (Southern France). Combining species distributions models and spatial graphs improves habitat connectivity and therefore the design of the development projects. Next, we demonstrate the positive impacts on peri-urban habitat connectivity of pooling and anticipating offsets in the suburbs of Lyon. In the last part, we demonstrate the implications of an anticipated and planned approach to the mitigation hierarchy on a planning scale. We consider both ecological connectivity and urban dynamics, in an attempt to minimize the ecological impacts of urban sprawl by avoiding urbanization of areas of highest ecological value and then enhance the application of biodiversity offsetting. This method is tested on projections for the Toulouse conurbation (Southern France) by 2040. Thus, this thesis presents an overall approach that can help to increase habitat connectivity and to improve the design of territorial development projects at different spatial and temporal scales. This methodology is based on freeware available to all practitioners. It will serve planners, designers, and decision-makers needing to ensure that there are no significant or irreversible effects on biodiversity, and environmental authorities making sure that all environmental issues are taken into account in the design of development projects.La biodiversité est confrontée à une érosion accélérée et est devenue une préoccupation environnementale mondiale ces dernières décennies. En France, la séquence Éviter–Réduire–Compenser (ERC) est un des outils réglementaires mis en place dans un contexte de destruction et de fragmentation des habitats d’espèces. Elle permet le développement des territoires tout en visant une absence de perte nette de biodiversité. Cependant, malgré les récentes évolutions réglementaires européennes et françaises, le triptyque ERC présente de nombreuses limites et enjeux d’ordre opérationnel. En positionnant nos travaux à l’interface entre recherche et opérationnalité, nous proposons un cadre méthodologique basé sur plusieurs approches de modélisation afin d’améliorer les processus d’évaluation et décisionnels aux différentes étapes d’aménagement, de la planification à l’opérationnel au moment de l’autorisation des projets. Dans une première partie du travail, nous intégrons les enjeux spatio-temporels de la biodiversité à l’ensemble de la séquence ERC, de l’évaluation des impacts potentiels au dimensionnement des mesures écologiques. À partir du cas précis de l’aménagement du Grand Stade de Lyon, nous montrons l’intérêt de combiner les modèles de distribution d’espèces et les graphes paysager pour identifier les réseaux écologiques et poser un cadre de calcul de l’équivalence écologique basé sur le volet fonctionnel de la biodiversité. Intégrer les dimensions spatiales et temporelles permet d’accroitre la connectivité des habitats et améliorer la conception des projets. Nous montrons ensuite qu’organiser la compensation à l’échelle des territoires en les intégrant aux réseaux écologiques améliore davantage les bénéfices et réduit le risque d’échecs des mesures. Notre démarche est présentée dans le contexte périurbain de l’Ouest de Lyon. Enfin, nous démontrons les implications d’une démarche anticipée et planifiée de la séquence ERC dans la planification stratégique des territoires. Pour cela, nous montrons dans le cadre de la Métropole de Toulouse l’intérêt d’étudier conjointement les dynamiques urbaines et écologiques pour mettre en place une stratégie de conservation de la biodiversité à l’horizon 2040 en assurant l’absence de perte nette sur les habitats d’espèces et leur connectivité selon différentes trajectoires d’urbanisation et de ratio de compensation. Cette thèse offre une approche globale pour orienter les décideurs et améliorer la prise en compte des fonctionnalités écologiques à différentes échelles spatiales et temporelles dans l’aménagement des territoires et l’application de la séquence ERC. Ce travail est basé sur des logiciels novateurs et accessibles pour tous les acteurs et constitue une contribution intéressante à l’appui des maitres d’ouvrage qui souhaitent s’assurer de l’absence d'effets significatifs ou irréversibles sur la biodiversité, et des autorités environnementales qui veillent à ce que l’ensemble des enjeux environnementaux soient bien pris en compte dans la conception des projets d’aménagement

Is there a spatial match between roadkill and mitigation measures identified by functional connectivity modeling?

Linear transportation infrastructure affects the ability of wildlife species to live and move through anthropized landscapes. Mitigation measures are thus needed to maintain population viability. Several methods have been employed to determine optimal locations for these measures, including connectivity modeling, which targets areas with the strongest connectivity and/or potential connectivity gains. However, these results are seldom compared to biological data, such as roadkill. The objective of our study is to: i) to gain a deeper understanding of the relationships between roadkill and connectivity, ii) to spatially identify road sections with a high risk of roadkill and, iii) to compare high-risk roadkill areas with the locations identified for potential mitigation measures. We performed a generalized linear model to explain occurrence and abundance of roadkill and predict high-risk roadkill areas. The mitigation measures corresponded to either i) existing crossing structures that could be enhanced to facilitate wildlife passage, selected from the initial connectivity or ii) new wildlife crossings designed to reconnect habitats identified through connectivity gains.Our results indicate that connectivity significantly influences the occurrence and abundance of roadkill. However, the high-risk roadkill areas only partially align with the locations designated for mitigation measures. Since some roadkill occurs outside of high-connectivity areas, factors other than connectivity must also be taken into consideration. This study offers valuable insights and underscores the complexity of the relationships between connectivity, roadkill, and mitigation efforts. Furthermore, by integrating spatial modeling, mitigation strategies, and roadkill data, this study contributes to a deeper understanding of corridor restoration areas and their importance in species conservation

Maximizing habitat connectivity in the mitigation hierarchy. A case study on three terrestrial mammals in an urban environment

International audienceEnvironmental policies and the objective of no net loss highlight the importance of preserving ecological networks to limit the fragmentation of natural habitats and biodiversity loss, especially due to urbanization. In the environmental impact assessment context, habitat connectivity and the spatio-temporal dynamics of biodiversity are crucial to obtaining reliable predictions that can support decision-making. We propose a methodological framework 1) to quantify the overall impact of a development project on the functioning of an ecological network, and 2) to select the best locations for implanting new habitat patches intended to enhance landscape connectivity. The amount of reachable habitat concept was applied to three representative terrestrial mammal species: the red squirrel, the Eurasian badger and the European hedgehog. All three species are recognized as vulnerable to human pressures and potentially affected by the construction of a new stadium in our study site, Lyon (Southern France). The method combines the species distribution model Maxent with the landscape functional connectivity model Graphab. The results showed that using any one of the avoidance and reduction measures on its own was unsuccessful in achieving the objective of no net loss when habitat connectivity is considered. However, the combination of new habitat patches and corridors offered a higher gain than distinct measures. This is especially important in the short term, when new hedgerow plantations have not yet developed enough to be used by the target species. Our findings indicate, first, the need to take the temporal scale into account in environmental impact assessment. We also show that applying the optimal scenario, constructed using a cumulative patch addition followed by a similar process testing a set of potential land-use changes, maximizes habitat connectivity. Our methodology provides a useful tool to increase target species' habitat connectivity within the mitigation hierarchy and to enhance development project design for increased environmental efficiency

Coupling spatial modeling with expert opinion approaches to restore multispecies connectivity of major transportation infrastructure

International audienceIt is widely recognized that major transportation infrastructures such as highways degrade habitats, increase the risk of collision mortality, and cause alterations in landscape connectivity by reducing connections between habitats due to the barrier effect. Wildlife crossings (underpasses and overpasses) have therefore become standard practice to reduce these effects on wildlife. Most studies aim to identify relevant locations for the creation of new wildlife crossings, but it is very rare for results based on modeling tools or animal movement records, for example, to be confronted with expert opinion and knowledge. Our paper provides a methodological framework combining modeling tools and field expertise from a multi-scale perspective. We used complementary connectivity metrics from graph theory to accurately quantify and spatialize the most relevant areas to improve habitat connectivity with multispecies conservation goals. The connectivity analysis was coupled with field expertise to take into account the local context, and technical and land feasibility. We prioritized existing road structures for improvement, found the best locations for new wildlife crossings, and made specific, costed technical recommendations. We empirically tested this approach on a large highway network in Northern France. This allowed us to define work principles to improve 109 existing road structures and to create underpasses or overpasses on 15 road sections. This innovative study for operational purposes has been a useful tool to assist the decision-making process of land-use planners who wish to improve wildlife crossings on major transportation infrastructures

Pooling biodiversity offsets to improve habitat connectivity and species conservation

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Environmental impact assessment of development projects improved by merging species distribution and habitat connectivity modelling

International audienceEnvironmental impact assessment (EIA) is performed to limit potential impacts of development projects on species and ecosystem functions. However, the methods related to EIA actually pay little attention to the landscape-scale effects of development projects on biodiversity. In this study we proposed a methodological framework to more properly address the landscape-scale impacts of a new stadium project in Lyon (France) on two representative mammal species exemplary for the endemic fauna, the red squirrel and the Eurasian badger. Our approach combined species distribution model using Maxent and landscape functional connectivity model using Graphab at two spatial scales to assess habitat connectivity before and after development project implementation. The development project had a negative impact on landscape connectivity: overall habitat connectivity (PC index) decreased by-6.8% and-1.8% and the number of graph components increased by +60.0% and +17.6% for the red squirrel and the European badger respectively, because some links that formerly connected habitat patches were cut by the development project. Changes affecting landscape structure and composition emphasized the need to implement appropriate avoidance and reduction measures. Our methodology provides a useful tool both for EIA studies at each step of the way to support decision-making in landscape conservation planning. The method could be also developed in the design phase to compare the effectiveness of different avoidance or mitigation measures and resize them if necessary to maximize habitat connectivity

Integrating a landscape connectivity approach into mitigation hierarchy planning by anticipating urban dynamics

International audienceUrbanization leads to land-use changes and landscape fragmentation, impacting natural habitats and their connectivity. In principle, many local decision-makers are obliged to adopt a mitigation hierarchy whereby development projects must be designed to avoid impacts on biodiversity, reduce, and ultimately compensate for the remaining impacts to reach the goal of no net loss (NNL) of biodiversity. In practice, however, both developers and regulators lack relevant practical tools to support their strategies to better anticipate and plan this mitigation hierarchy. More importantly, the available tools generally ignore connectivity issues and ecological constraints. Here, we propose an original methodology that anticipates future urban needs under different development scenarios and selects the most relevant strategies for biodiversity offsets (BO). We used a spatialized digital simulator (called SimUrba) to model fine-scale urban dynamics, combining it with ecological networks modelling based on graph theory to assess the environmental impacts of urbanization on a habitat connectivity index for focal species. We test the different outcomes produced by adopting two offset ratios (1:1 and 2:1) using this approach. The methodology is applied to empirical data on the future urban sprawl of a large French city up to 2040 under two realistic development scenarios currently discussed by policy-makers, and on 20 species that we grouped by type of habitat. Our results reveal that that the most highly impacted species are those associated with open and semi-open areas, and cultivated plots. Then, we identify the most promising cells for BO implementation to compensate for negative effects on habitat area, according to gains in habitat connectivity. We further show that using both private and public land can maximize habitat connectivity by including larger plots and reducing the number of plots needing long-term monitoring. Finally, we demonstrate that using standard offset ratios that ignore connectivity issues is very risky and can compromise any BO objective. Overall, we show that this framework provides decision-makers with a valuable and precise strategic tool that articulates land-use planning with ecological constraints to identify whether, how and where NNL objectives can be achieved

Améliorer la transparence écologique des grandes infrastructures de transport. Le cas du réseau autoroutier du groupe Sanef

International audienceMajor transport infrastructures affect landscape connectivity and lead to implement mitigation measures such as wildlife crossings. We propose in this study a methodological framework applied to a large highway network in the North of France that allows to identify i) existing road structures to be improved as a priority through an ecological functionality index, and ii) favorable locations to create new wildlife crossing regarding habitat connectivity gains. We implemented a multispecies approach using 9 characteristic species included in the French list for national consistency of the green and blue corridor, defined by the French National Museum of Natural History, and grouped from their habitat preferences. The originality of this study lies in the identification of existing road structures to be improved and new wildlife crossings to be created to improve ecological continuity, but above all by the combining of a modeling approach and operational expertise to specify technical details. This innovative study for operational purposes was a useful tool to support decision-making of land-use planning stakeholders which want to improve the crossing of transport infrastructure by wildlife.Les grandes infrastructures de transport affectent les réseaux écologiques et nécessitent la mise en place de mesures d’atténuation tels que les passages à faune. Nous proposons dans cet article un cadre méthodologique, appliqué à un vaste réseau autoroutier dans le Nord de la France, qui permet d’identifier i) les ouvrages existants à améliorer en priorité à travers un indicateur de fonctionnalités écologiques permettant d’identifier les zones les plus stratégiques en termes de connectivité où une amélioration des fonctionnalités des ouvrages serait le plus profitable pour la faune, et ii) les emplacements favorables pour créer de nouveaux ouvrages au regard des gains générés sur la connectivité des habitats. Une analyse multi-espèces a été mise en œuvre à partir de 9 espèces caractéristiques de la Trame verte et bleue réparties en 3 groupes liées aux préférences d’habitats. L'originalité de notre approche réside en l’identification des ouvrages existants à améliorer et des nouveaux ouvrages à créer pour favoriser les continuités écologiques, mais surtout par le couplage d’une approche de modélisation et d’une expertise opérationnelle tenant compte du contexte local pour préciser les détails techniques. Cette étude innovante à visée opérationnelle a été une véritable aide à la décision pour le maitre d'ouvrage et les services de l'État, soucieux d'améliorer le franchissement des infrastructures de transport par la faune

From single to multiple habitat connectivity: The key role of composite ecological networks for amphibian conservation and habitat restoration

International audienceMany graph-based studies consider just one habitat type (breeding habitat) and one ecological process (dispersal) when measuring connectivity. However, in the course of their life cycle, some species use different habitats and are particularly sensitive to their spatial arrangement. We propose a new graph modeling approach that considers heterogeneous habitats and movements when assessing connectivity. Our hypothesis is that a multiple habitat approach is more relevant than a single habitat approach for studying the relationships between connectivity and composite habitat species occurrence. We constructed a bipartite graph with separate categories of nodes for aquatic and terrestrial habitats and an inter-habitat link set. Different connectivity values were measured from the graph depending on the ecological process under study. We then compared our models against field observation data for amphibian communities and tested whether multiple habitat connectivity models provide better predictions. Multiple habitat connectivity was as effective as single habitat connectivity, and often more so, in explaining the presence, abundance, and species richness of amphibian communities. Application to habitat restoration revealed that connectivity gains vary greatly depending on the ecological process, emphasizing the importance of links connecting habitats of different types. Multiple habitat graphs appear promising for incorporating habitat and movement heterogeneity into ecological network modeling. We encourage further theoretical and empirical work on multiple habitat connectivity to consolidate the results and evaluate its full potential, especially for global change issues