Plant species richness increases resistance to invasion by non‐resident plant species during grassland restoration

Abstract

AbstractQuestionsDuring restoration of bare subsoil, are planted grassland communities with low species richness more susceptible to invasion by non‐residents than communities augmented by additional species? What are the mechanisms of invasion resistance in early succession?LocationLexington, Virginia, USA (37.8°N, −79.4°W).MethodsWe planted 62 3 × 3 m plots on compacted clay subsoil with 20–21 replicates of three, 12 and 24 native species. Plots were sampled non‐destructively using a stratified random point‐intercept method each summer for 5 yr to determine number of species and percentage cover per species, which were classified as residents (planted), internal non‐residents (planted in other plots) or external non‐residents.ResultsA negative relationship between planted species richness and invasion developed by the fourth year after planting and strengthened thereafter. Plots consisting of a single, highly dominant, resident C3 grass species were vulnerable to invasion. With the exception of one species, which seems to have overcome resistance with a high seed rain, external non‐resident species were less diverse and less abundant in higher diversity plots.ConclusionsIncreased planted species richness was correlated with increased resistance to invasion by non‐residents, and we attribute this effect to a combination of the sampling effect and species complementarity, potentially augmented by high species dominance/low evenness in the low species richness plots.