Effects of restoration on plant species richness and composition in Scandinavian semi-natural grasslands

Plant species richness in rural landscapes of northern Europe has been positively influenced by traditional management for millennia. Owing to abandonment of these practices, the number of species-rich semi-natural grasslands has decreased, and remaining habitats suffer from deterioration, fragmentation, and plant species decline. To prevent further extinctions, restoration efforts have increased during the last decades, by reintroducing grazing in former semi-natural grasslands. To assess the ecological factors that might influence the outcome of such restorations, we made a survey of semi-natural grasslands in Sweden that have been restored during the last decade. We investigated how plant species richness, species density, species composition, and abundance of 10 species that are indicators of grazing are affected by (1) the size of the restored site, (2) the time between abandonment of grazing and restoration, (3) the time elapsed since restoration, and (4) the abundance of trees and shrubs at the restored site. Only two factors, abundance of trees and shrubs and time since restoration, were positively associated with total species richness and species density per meter square at restored sites. Variation in species composition among restored sites was not related to any of the investigated factors. Species composition was relatively similar among sites, except in mesic/wet grasslands. The investigated factors had small effects on the abundance of the grazing-indicator species. Only Campanula rotundifolia responded to restoration with increasing abundance and may thus be a suitable indicator of improved habitat quality. In conclusion, positive effects on species richness may appear relatively soon after restoration, but rare, short-lived species are still absent. Therefore, remnant populations in surrounding areas may be important in fully recreating former species richness and composition.