Effects of year-round grazing on the vegetation of nutrient-poor grass- and heathlands-Evidence from a large-scale survey

Year-round grazing by cattle and horses has recently become a common practice in conservation management in north-western Europe. Though many projects claim positive effects on vegetation development, evidence is still largely anecdotal. There are no comprehensive regional surveys allowing the detection of general patterns beyond single case studies. This applies even more to nutrient-poor sites where year-round grazing systems were only recently established and concerns about potentially negative effects on plant diversity are still prevalent. Hence, this study investigates the impacts of year-round grazing on plant species richness, species composition, and vegetation structure on nutrient-poor sites using a regional multi-site approach. Surveys were carried out at five different study sites in the diluvial plain of northwestern Germany and the Netherlands comprising sand grasslands, dry grasslands, and heathlands. Results show overall positive effects of grazing: Plant species richness, the number of endangered plant species, and the proportion of open soil were increased significantly. Contrary, green biomass, litter cover, vegetation height, and the cover of woody species significantly decreased. At grazed sites there were more small, light-demanding species than taller, mesophilic species. A distinct decrease of ruderal species and an increase of species following a competitive strategy was observed at abandoned sites. Based on broad regional evidence, we conclude that year-round grazing is a suitable tool for the restoration and management of open habitats on nutrient-poor sandy sites. Low sward biomass and poor nutritional quality raise, however, concerns about adequate fodder supply and animal welfare.