Ruellia simplex

Abstract: Question Planting or seeding native species after control of invasive species can limit re-invasion and hasten establishment of native species. Ruellia simplex (Mexican petunia) invades floodplain forests in Florida, and is controlled with glyphosate herbicide. Will herbicide application used to control this weed allow establishment of native vegetation and limit R. simplex? Location Floodplain forest altered by stormwater run-off, Lake Jesup Conservation Area, Sanford, FL, US. Methods We evaluated re-vegetation following herbicide application to control R. simplex. For re-vegetation, we planted or seeded native species (Andropogon glomeratus, Juncus effusus, Panicum longifolium, Solidago fistulosa) and measured stem density, percentage cover, above-ground biomass and species richness for 1 yr. We compared the results to those from control plots (i.e. no herbicide, no re-vegetation) and plots where R. simplex was sprayed with herbicide but not planted or seeded with native species. Results Unassisted re-colonization (i.e. plots where R. simplex was sprayed but not planted or seeded with native species) did not result in native plant restoration. Re-vegetation treatments (i.e. plots where R. simplex was sprayed and planted or seeded with native species) did not restore native vegetation; nor did re-vegetation treatments reduce R. simplex stem density, percentage cover or biomass compared to control plots. However, total species richness, including native and exotic species richness, increased in plots planted with a native plug mix compared to control plots (i.e. no herbicide, no re-vegetation). Native species failed to germinate in all seeding treatments. Plugs had adequate survival (2–57% depending on species) but did not prevent re-invasion of R. simplex. Re-invasion of R. simplex occurred in plots despite application of glyphosate herbicide and re-vegetation treatments. Conclusions Re-vegetation by seeding or planting did not establish native vegetation in the first year, instead, R. simplex reinvaded. Abiotic and biotic site conditions, e.g. invasive species propagule pressure and altered soil nutrients, may have limited seed germination and survival of planted seedlings. More research is necessary to determine if a reduction in invasive species propagules through repeated herbicide application coupled with planting native species results in native plant restoration in the longer term.

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