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

Authors

  • Carrie Reinhardt Adams,

    Corresponding author
    1. University of Minnesota, Department of Horticultural Science, 305 Alderman Hall, 1970 Folwell Avenue, St. Paul, MN 55108, USA
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  • Susan M. Galatowitsch

    1. University of Minnesota, Department of Horticultural Science, 305 Alderman Hall, 1970 Folwell Avenue, St. Paul, MN 55108, USA
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  • Nomenclature: Gleason & Cronquist (1991).

Corresponding author; present address University of Florida, Environmental Horticulture Department, PO Box 110675, Gainesville, FL 32611–0675, USA; Tel. +1 352392183; Fax +1 3523921413; E-mail creinhardt@ifas.ufl.edu;

Abstract

Question: 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.

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