The transition from invasive species control to native species promotion and its dependence on seed density thresholds

Abstract

AbstractQuestion: Does the seed density of invasive species affect establishment by native species in a bare ground context (following invasive species control efforts), and is it possible to promote transition to a native species dominated state by manipulating sowing density of the native community?Location: Experimental wetland basin in Chanhassen, Minnesota, USA.Methods: A mesocosm experiment investigated the influence of Phalaris arundinacea (invasive species) propagule pressure on establishment of native wet meadow species in the context of a newly restored wetland. Mesocosms were sown with P. arundinacea (0, 10, 50, 100, or 500 seeds/m2) and a mix of native species (3000 or 15000 seeds/m2).Results: When planted at densities > 100 seeds/m2, P. arundinacea increased suppression of native species. Also, high native seed density suppressed P. arundinacea biomass production. This effect was more pronounced when P. arundinacea seed density was high (> 100 seeds/m2), but high native seed density (15000 seeds/m2) did not suppress recruitment of P. arundinacea from seed.Conclusions: The transition from post‐control bare ground (a common result of efforts to control invasive species) to native species establishment depends on both native species and invader seed density. These results suggest that a threshold of P. arundinacea propagule pressure exists, beyond which transition to a native community is less likely without management intervention. P. arundinacea can establish in the presence of a newly developing native plant community, even at very low densities of P. arundinacea seed. Invader control (following initial site clearing efforts) is essential to native species establishment.