Plant communities and the reproductive success of native plants after the invasion of an ornamental herb

Abstract

The effects of plant invasions on plant communities are often assessed at a few sites or in a particular type of habitat, while studies in different habitat types are scarce. We investigated plant communities in the presence and absence of the invasive ornamental herb, Lupinus polyphyllus, in four habitat types: meadow, forest, road verge and wasteland, in two geographic regions by comparing vascular plant species richness, vegetation structure based on species traits, community composition and the reproductive success of native plant species at invaded and non-invaded locations. The invader was associated with declines in the number of vascular plant species in all habitat types but was unassociated with differences in plant community composition in terms of species identity or species relative cover. However, sites with large lupin invasions (≥1,000 m2) contained fewer vascular plant species, a larger proportion of clonal species and more lighter-seeded species than sites with small invasions. The reproductive output of native plants varied across habitats from declines to increases in the presence of L. polyphyllus, and depended on species status (meadow, non-meadow species) rather than species identity, with meadow species generally showing an increase in the reproductive output in the presence of the invader. Overall, our results demonstrate that lupin invasions are associated with declines in local plant species richness across habitats. Although we did not detect systematic differences in species composition between invaded and non-invaded locations, species with particular traits may still be more persistent in invaded plant communities than others.