The benefits of sward diversity for cultivated grasslands

Increased emphasis on the multifunctionality of European agriculture has called for a reinvestigation of the use of mixtures in productive grasslands. Recent ecological research, carried out in relatively species-rich and nutrient poor systems, has indicated that ecological processes may be more effective when species diversity increases. If this would also be valid under nutrient-rich intensively managed conditions, increased crop diversity in species-poor agronomic systems could improve the provision of ecosystem services. We have recently developed an experimental and modelling framework which allows us to separately estimate the contributions of interactions in species mixtures by manipulating relative abundance. We applied our methodology to data from a common experiment at 28 European sites, using mixtures consisting of four agronomic species belonging to four functional groups. Our results indicate strong benefits of sward diversity in intensive cultivated grassland systems. Generally, mixtures provided more forage yield than could be expected on the basis of the performance of all species in monoculture. Averaged across sites we found that the performance of mixtures generally even exceeded that of the best performing monoculture. Mixtures strongly reduced the incidence of unsown species in the sward. The diversity effect was consistent over a huge range of environmental conditions, thus adding generality to our findings. It appears to persist over three harvest years and even under very intensive management. In contrast to other biodiversity experiments, our methodology has allowed us to determine the significance of species' evenness for diversity effects.