creation of diverse prairie-like communities

We tested the prediction that we are more likely to create persistent, species-rich plant communities by increasing the number of species sown and allowing communities to assemble over six or seven growing seasons. Treatments consisted of four initial seed mixtures comprising 4, 8, 12 and 16 species that represent four functional groups C3 graminoids, C4 grasses, N-fixing species, and late-flowering composites) that predominate within North American prairies. Once seeded, half of the plots were left alone to develop without subsequent reseeding. To provide multiple opportunities for establishment, we reseeded the remaining plots with any target species that failed to establish after two growing seasons. There were two 16 x 16 m (256 m2) replicates per treatment established in 1994 and 1996 on former agricultural land. Annually, we measured total species richness and evenness, total cover, and establishment success defined as target species richness and total percentage cover by target species, collectively. In some instances, significant treatment x year interactions indicated that treatment effects on variables varied among years. Both richness and rate of establishment of target communities were higher in the more species-rich mixtures. Moreover, richness of resident species in the plots declined with increasing target species richness. Reseeding had no measurable effect on any of the variables, nor on the eventual establishment of target communities or individual target species. Our results, indicating that establishment of species-rich plant communities can be enhanced by starting with larger numbers of species at the outset, have implications for projects in which community biodiversity creation and maintenance are key goals.