Preventing plant invasions at early stages of revegetation: The role of limiting similarity in seed size and seed density

Revegetation of roadsides is an opportunity for grassland restoration, yet these habitats are prone to be colonised by invasive alien plant species (IAS). Therefore, the selection of seed mixtures for revegetation should consider potential competition with IAS present in the soil seed bank or arriving by traffic-related seed rain. We investigated whether the limiting similarity hypothesis, in terms of plant seed-size-output strategy, could be used to design native grassland communities resistant to IAS. In a greenhouse experiment, a small- or a large-seeded IAS was sown into factorial combinations of two native communities with small or large seed-size-output strategies at two sowing densities. Height and aboveground biomass of the IAS were measured after four and eight weeks, respectively. Small-seeded native communities at high density were highly effective in suppressing the small- and large-seeded IAS, mostly controlled by a density effect. Thus, limiting similarity in seed-size-output strategy only partly explained resistance to IAS, while density-driven suppression was more effective.