Populations of a shrub-feeding butterfly thrive after introduction of restorative shrub cutting on formerly abandoned calcareous grassland

Abstract

Calcareous grasslands are one of the most species-rich semi-natural habitat types. However, area and species richness have considerably decreased, particularly due to the cessation of grazing or mowing. Accordingly, habitat restoration has become an important issue in the conservation of these grasslands. The aim of this study was to analyse the role of shrub cutting as a measure to restore habitats of the target butterfly Satyrium spini (Denis and Schiffermuller 1775) on formerly abandoned calcareous grasslands. We compared host plant density and occupancy, as well as egg batch density and size between cut, regularly managed and fallow patches. In total, we counted 3372 Rhamnus cathartica host plants on 17 calcareous grassland patches. On 309 (9 %) of these plants, we found a total of 490 batches containing 1168 eggs. Both R. cathartica and S. spini responded rapidly to restoration: Shrub cutting promoted the rejuvenation of the host plant, resulting in a strong population increase of the butterfly species four years after shrub cutting. The density of the preferred small host plants (growth height < 130 cm), their occupancy, as well as the density and size of the batches on these plants, clearly exceeded those of small plants on fallow and even on traditionally managed calcareous grasslands. Based on this study, we recommend shrub cutting on calcareous grasslands as both a restorative and regular management measure for S. spini habitats. Due to the increasing demand for fuel wood, shrub cutting in overgrown grasslands might even no longer be constrained by economic reasons.