The research project for this PhD set out to provide a best practice example of bringing together industry (Hanson Heidelberg Cement Group), a charitable body (The Parks Trust), non-departmental public body (Environment Agency) and academia (Cranfield University). The Parks Trust (landowner) and Hanson (quarry operator) worked together with the vision of creating a new floodplain forest landscape along a 1 km reach of the River Great Ouse following extraction of gravels from the site. It was the first project of its kind in the United Kingdom where planning permission was obtained specifically for the creation of a floodplain forest habitats post quarrying. The aim of the PhD research was to determine appropriate ecological approaches to apply to the assessment and future monitoring of habitat outcomes of a floodplain forest restoration project at a mineral extraction site. A central element of the research was the design of a scientifically justified monitoring programme, with key variables determined being: soil characteristics, water quality, vegetation development, site topography and water table level data. An Adaptive Monitoring Framework (AMF) was chosen to set the proposed monitoring within which was complemented with the hypothesis - The ratio of wet/dry vegetation within the floodplain forest is determined by the site topography and water table level. The hypothesis was tested by analysis of the key variables through fieldwork and existing data sources supplemented with a study of the water table level interaction with two typical floodplain forest tree species (Salix viminalis and Populus trichocarpa x deltoides) in a glasshouse experiment. Findings from the field and experimental research were then used within a spatially based landscape ecology scenario approach to identify the most suitable areas of the study site for specific species planting according to soil-water levels and topography in the floodplain forest. Outputs of this research enhance understanding of the key aspects to consider when assessing floodplain forest re-creation/restoration and enable guidelines and recommendations to be developed for land managers based on a long-term and an adaptive ecological monitoring approach. These management guidelines and recommendations based on a systematic scientific approach applied within the research should be appropriate to other similar restoration projects. The research provides the background evidence on what should be measured to determine the environmental changes of the floodplain forest habitat restoration as it develops towards restoration success.

Mining has caused ecosystem losses worldwide, with surface mining disturbing >2.4 million hectares in the United States since 1930. The Appalachian region of the US is home to extensive temperate deciduous forests that provide many ecosystem services and economic benefits. However, >400,000 hectares of forest have been lost due to surface coal mining, with most not being restored back to native forests or other productive land uses. These areas are left fragmented, heavily modified, unmanaged, and densely invaded by non-native plants. Autumn olive (Elaeagnus umbellata) is one of the most prevalent invasive species on reclaimed mines in Appalachia and viewed as one of the main hindrances to the successful reclamation of mined land to restore native forests. In order to better assess the impact autumn olive can have on reclamation success, we characterize autumn olive's performance in various reclamation scenarios and also how the management of autumn olive affects hardwood tree establishment. We review how exotic species impact restoration outcomes, and advocate for a better understanding of how these species could contribute towards a more ecological understanding of reclamation. Reclamation goals are currently assessed after 5 years, prioritizing short-term goals (e.g. erosion control) instead of longer-term goals such as the return of ecosystem function. With a better understanding of plant function and ecological processes, we hope to continue to advance successful reclamation on surface mined lands. / Master of Science in Life Sciences

L’écologie de la restauration est une discipline scientifique qui a vu le jour il y a une quarantaine d’années pour tenter de compenser les impacts négatifs du développement des sociétés sur les écosystèmes. Aujourd’hui, suite à des méta-analyses planétaires révélant le succès relatif des opérations de restauration écologique, une nouvelle question émerge : faut-il restaurer activement ou laisser en libre évolution les écosystèmes dégradés ? C’est dans ce contexte que ce projet de thèse a eu lieu avec une démarche qui s’est voulue pluridisciplinaire et a porté sur l’étude de l’impact de carrières sur la steppe méditerranéenne de Crau (Bouches-du-Rhône, France). Deux cas ont été pris en compte, (i) d’anciennes carrières exploitées dans les années 1970 et abandonnées présentant une diversité de modalités d’exploitation ou de réaménagement et, (ii) une carrière encore en cours d’exploitation dont la législation oblige la remise en état. L’objectif est de mieux identifier les éventuels verrous scientifiques en matière de connaissances pour la restauration et mieux définir les attentes sociétales afin de proposer au final une stratégie générale destinée à servir à la gestion future de ces écosystèmes. Les recherches de cette thèse se sont basées sur deux grandes questions, réflexions : (1) Les opérations de restauration écologique mises en place permettent-elles de restaurer l’écosystème de référence (= ici l’écosystème préexistant) ? En comparant différents traitements de restauration sur le long terme (transfert de sol selon différentes modalités, dépôts de matériaux anthropogéniques, absence de réhabilitation), nous avons pu montrer que le transfert de sol reste une bonne méthode, surtout lorsque les caractéristiques initiales du sol sont respectées. Néanmoins, il ne compense toujours pas à moyen-terme (35 ans) la destruction de l'écosystème préexistant : le sol et la communauté végétale de la steppe de référence ne sont pas encore complètement rétablis. Une deuxième technique de mélange de sol lorsque le sol originel n’est plus disponible a également été testée, mais elle ne présente pas non plus un succès total de restauration à court terme (3 ans). Une deuxième question s’est donc posée en parallèle: (2) Sans restauration active, quelle est la valeur de la biodiversité générée par les activités humaines ? Et plus globalement, quelles natures voulons-nous ? Les carrières ont détruit l’écosystème steppique qui préexistait mais ont créé également de nouvelles conditions (pédologiques, de nouveaux habitats) qui soutiennent le fonctionnement et la connectivité d’espèces pionnières et abritent une importante biodiversité patrimoniale absente de l’écosystème d’origine. De plus, la comparaison entre les paysages de carrières et l’écosystème de référence auprès de différents acteurs territoriaux et du grand public a montré que les anciennes carrières sont perçues comme étant beaucoup plus naturelles que la steppe de référence et qu’elles sont également associées à une importante biodiversité. Ces résultats pourraient donc réorienter les choix de restauration ou de gestion, afin de choisir entre 1) ce qui est actuellement recommandé (une restauration active appliquée en fin d’exploitation avec l’écosystème historique en référence) et 2) une libre expression de la nature férale encore appelée restauration passive (avec ou pas réaffectation initiale ; i.e. où l’écosystème de référence est différent de l’écosystème préexistant). / Restoration ecology is a scientific discipline that has emerged forty years ago to try to compensate the negative impacts of society development on ecosystems. Today, following global meta-analyzes revealing the relative success of ecological restoration, a new question emerges: should we actively or passively restore degraded ecosystems? It is in this context that this thesis project took place with a multidisciplinary approach and focused on the study of quarrying impacts on the Mediterranean steppe of Crau (Bouches-du-Rhône, France). Two cases were taken into account: (i) old quarries operated in the 1970s and abandoned then, presenting a variety of exploitation types or rehabilitation modalities, and (ii) a quarry still in the process of exploitation, the legislation now requiring repairs. The aim is to better identify possible scientific obstacles in the field of knowledge for ecological restoration and better define societal expectations in order to finally propose a general strategy intended to serve the future management of these ecosystems. The research of this thesis was based on two major questions, reflections: (1) Do ecological restoration actions restore the reference ecosystem (= the pre-existing ecosystem)? By comparing different long-term restoration treatments (various types of soil transfers, anthropogenic deposits, lack of rehabilitation), we were able to show that soil transfer is still the best method, especially when the initial characteristics of the soil are respected. However, it still does not compensate in the medium term (35 years) for the destruction of the pre-existing ecosystem: the soil and the plant community of the reference steppe are not completely restored yet. A second soil mixing technique used when the original soil is no longer available has also been tested, but it is not very successful either in the short-term (3 years). A second question arose in parallel: (2) Without active restoration, what is the value of biodiversity generated by human activities? And more generally, what kind of nature do we want? Quarries have destroyed the pre-existing steppe ecosystem but have also created new conditions (soil, new habitats) that support the functioning and connectivity of pioneer species and shelter important heritage biodiversity that is absent from the pre-existing ecosystem. In addition, the comparison between the quarry landscapes and the reference ecosystem landscapes with different stakeholders and the general public has shown that the old quarries are perceived as being much more natural than the reference steppe and that they are also associated to an important biodiversity. These results could therefore reorient the choice of restoration or management, in order to choose between 1) what is currently recommended (active restoration applied after the end of quarry exploitation with the historical ecosystem as a reference) and 2) the free expression of feral nature also called passive restoration (with or without reclamation, i.e. where the reference ecosystem is different from the pre-existing ecosystem).