Using a two-phase sowing approach in restoration: sowing foundation species to restore, and subordinate species to evaluate restoration success

Questions: Is it possible to restore a target herbaceous plant community on ex-arable land by sowing foundation species? What is the impact of sheep grazing on the restoration of this ecosystem? How can we rapidly evaluate the success of restoration methods? Location: Nature reserve of the plain of La Crau, southeast France (43° 31′ N, 4° 50′ E) Methods: In an ex-arable field, we sowed an indigenous species mix in 2007. This was composed of two perennial species dominant in the reference grassland ecosystem (Brachypodium retusum, Thymus vulgaris) and one annual species (Trifo-lium subterraneum) also found on the reference grassland and which is well-known for its ability to quickly cover bare soil. These three species are called foundation species as they play an essential role in structuring the restored ecosystem community. To investigate the significances of the foundation species on community dynamics, four subordinate species were sown 1 yr later: Taeniathe-rum caput-medusae, Linum strictum, Evax pygmaea and Asphodelus ayardii. The subordinate species are typical plants of the reference grassland which describe well this vegetation type. Results: Sowing foundation species was an effective means of reintroducing them. Their presence in the ex-arable field very rapidly promoted establishment of grassland species and impeded establishment of weeds. When grazing was excluded, the foundation species covered the ground, particularly with Trifolium subterraneum, which reached 54% ground cover. Subordinate species established better on the foundation species sown treatment and on the grazed treatment. Conclusion: In the short term, sowing indigenous foundation species and maintaining grazing seems to be a good method to restore grassland plant communities that have a poor ability to re-establish spontaneously. This study also demonstrates that sowing and monitoring of subordinate species is an effective method to rapidly test whether a particular restoration protocol will have a positive effect on community assembly and development.