Dispersal limitation of plant diversity influences biomass production in montane European grasslands

Recently, there has been an increasing demand for the incorporation of dispersal limitation issues into biodiversity-ecosystem function research. Dispersal can influence the local diversity of a habitat, but its potential role for ecosystem processes such as productivity has not been considered. We set up a seed addition experiment across 20 semi-natural montane grassland sites in Germany, where plant species diversity was not related to biomass production in control plots. Local plant species richness increased after adding seeds to the established plant communities, and this increase was highest in grasslands with intermediate productivity. This indicates that the hump-shaped model is the limiting outline of the natural diversity-productivity relationship. Moreover, increased diversity after adding seeds was associated with increased biomass production, extending results of earlier garden experiments to natural grasslands. Finally, overcoming dispersal limitation resulted in a hump-shaped relationship between diversity and productivity, indicating that dispersal limitation was the reason why this had not been observed in control plots. We conclude that in natural communities the effects of dispersal on local diversity substantially affect ecosystem processes.