Ecosystem restoration has been identified as one approach to slow down the loss of biodiversity and to protect all the biodiversity-based goods and services from which humankind benefits. Restoration feeds from knowledge coming from both community ecology and restoration ecology. The objectives of the thesis are to provide insights on both the dynamics of a mediterranean steppe after changes in land-use and the implementation of techniques which could be applied to restore this ecosystem after severe anthropogenic disturbances. The thesis takes as a study object the La Crau Mediterranean steppe, and especially former cultivated fields to study the recovery after cultivation and the Cossure large scale rehabilitation project to experiment rehabilitation and restoration techniques. Concerning dynamics after severe exogenous anthropogenic disturbances, we confirmed the low resilience of the steppe plant community both at mid- (30-40 years) and long-term (150 years) while the resilience of soil parameters and mycorrhizal infestation rate are effective on the long-term. Moreover we confirmed the role played by the three filters in the plant community recovery and found that for the La Crau steppe, this is firstly driven by the abiotic filter, then by the dispersion filter and finally by the biotic filter. Given this low resilience, we tested several restoration techniques applied at large-scale within the Cossure rehabilitation project: nurse species seeding, topsoil removal, hay transfer and soil transfer. In order to assess the efficiency of restoration techniques we developed indices to measure the community structure integrity, disentangling lower and higher abundances compared to the reference. The best results were obtained with soil transfer, followed by topsoil removal, then nurse species seeding and finally hay transfer. The research conducted for this thesis shows that current knowledge in ecological restoration makes it possible to restore at least partially some La Crau ecosystem components, but ought to lead us to understand the importance of in situ conservation of natural habitats as a better alternative to restore them after they were destroyed
