Applying biodiversity and assembly theory to increasing extensive grassland productivity whilst maintaining high diversity

Recent advances in plant ecology include research on concrete effects of plant diversity on ecosystem functions and processes, with a main focus on the stimulation of community productivity and nutrient cycling. Much of this experimental research has occurred in mesic relatively productive grassland habitats, and has included weeding to maintain diversity gradients. More recent work however, has started to focus on whether naturally assembling communities may also benefit from higher diversity in terms of both allowing sustained productivity as well as maintaining diversity.Grassland productivity as well as diversity are set to become an important simultaneous goal for land managers and farmers, who are interested in increasing both productivity as well as diversity of their land. Bullock et al. (2001, 2007) sowed high and low diversity seed mixtures onto ex-arable land to restore them to species-rich chalk grasslands and found that sowing diversity significantly improved both overall productivity as well as diversity of the sites. In community assembly, the timing of arrival of different plant functional groups may affect productivity even more than the richness of species sown. My group has been testing how priority effects (species that arrive first influencing further development) of sowing different plant functional groups earlier than others affects productivity and diversity of the ensuing community. Initial results confirm biodiversity-ecosystem functioning studies in that sowing more diverse mixtures but especially manipulating the timing of arrival of different functional groups can drive further assembly and positively affect ecosystem properties. The stability and strength of different priority effects over time is now being investigated in a field experiment in Jülich called the Priority Effect Experiment