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Réhabilitation écologique d’écosystèmes dégradés par l’exploitation des carrières : faire avec, refaire ou laisser faire la nature ?

Abstract : 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).
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Submitted on : Monday, March 18, 2019 - 10:46:11 AM
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  • HAL Id : tel-02070639, version 1
  • IRSTEA : PUB00060100

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Julie Chenot. Réhabilitation écologique d’écosystèmes dégradés par l’exploitation des carrières : faire avec, refaire ou laisser faire la nature ?. Biologie végétale. Université d'Avignon, 2018. Français. ⟨NNT : 2018AVIG0344⟩. ⟨tel-02070639⟩

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