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

AbstractQuestions: Is it possible to restore a target herbaceous plant community on ex-arable land by sowing foundation species? What is the impact of sheep grazingontherestorationofthisecosystem?Howcanwerapidlyevaluatethesuccessofrestorationmethods?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.Thiswascomposedoftwoperennialspeciesdominantinthereferencegrasslandecosystem(Brachypodiumretusum,Thymusvulgaris)andoneannualspecies(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 calledfoundation species as they play an essential role in structuring the restored eco-systemcommunity.Toinvestigatethe significances ofthe foundationspecies oncommunity dynamics, four subordinate species were sown 1 yr later: Taeniathe-rum caput-medusae, Linum strictum, Evax pygmaea and Asphodelus ayardii. The sub-ordinate speciesare typical plantsofthe referencegrassland which describe wellthisvegetationtype.Results: Sowing foundation species was an effective means of reintroducingthem. Their presence inthe ex-arable fieldveryrapidly promoted establishmentof grassland species and impeded establishment of weeds. When grazing wasexcluded,thefoundation species covered the ground,particularlywithTrifoliumsubterraneum,whichreached54% groundcover.Subordinatespeciesestablishedbetteronthefoundationspeciessowntreatmentandonthegrazedtreatment.Conclusion:Intheshortterm,sowingindigenousfoundationspeciesandmain-taining grazing seems to be a good method to restore grassland plant communi-ties that have a poor ability to re-establish spontaneously. This study alsodemonstrates that sowing and monitoring of subordinate species is an effectivemethod to rapidlytestwhetheraparticularrestorationprotocolwillhaveaposi-tiveeffectoncommunityassemblyanddevelopment.IntroductionGrassland ecosystems are under threat in many parts ofthe world. Their destruction and fragmentation are conse-quences of human use, in particular agricultural activities(Walker et al. 2004). Ploughing, stone removal and fertil-ization decrease their plant species richness, and changetheir floristic composition even after crop abandonment(Lawson et al. 2004; Romermann et al. 2005). Plant com-munities shift towards a dominance of indigenous weeds(Romermann et al. 2005), which are spontaneous speciespromoted by human activities and characterized by highreproduction, dispersion and colonization capacity (Zim-dahl 2007). Grassland species, in particular perennial spe-cies, are not adapted to modern cultural landscapes(Lawson et al. 2004; Critchley et al. 2006; Nordbakken