Propagule pressure is a known mechanism linked to invasion worldwide and serves as a strong predictor of invasion success. The role of propagule pressure in determining invasion success into a community is mediated by the biotic resistance of the receiving community, as well as by the traits of the arriving species. The integration of factors related to invasion success can provide a framework for restoration wherein invasion mechanisms are used in reverse to promote restoration. By applying a gradient of five native propagule pressures to sites dominated by invasive species, we explored how increasing native propagule pressure contributes to native reestablishment in invaded annual plant communities in Southern California. We also tested the biotic resistance to native species reestablishment in communities that varied in invasive species composition. Specifically, we tested how functional trait composition of the invasive communities affected native species reestablishment.
Results/Conclusions
Increased levels of native propagule pressure reduced the abundance and seed production of resident invasive species and increased the abundance and seed production of native species. Effects of negative density dependence were observed in high propagule pressure treatments but did not reduce native species establishment or total seed production across propagule pressure treatments. The functional trait composition of the varying invasive communities did not predict the success of native species establishment in any propagule pressure treatments, indicating that native species establishment was achieved solely through seeding at high density. Our results highlight the importance of large native species introduction events for successful native reestablishment and the reduction of invasive species abundances in restoration efforts.