Introduce organisms to control problematic plants: freshwater marshes
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
This action involves biological control: managing the abundance or distribution of problematic organisms via their enemies. Enemies of problematic plants could be disease-causing microorganisms (e.g. a virus or a fungus), insects, fish or even other plants (to compete with or parasitize problematic plants). Biological control could be particularly effective for non-native problematic plants: their success in their new range may be due to escape from natural enemies in their native range (Keane & Crawley 2002). Caution: Organisms introduced for biological control can themselves become problematic pests (e.g. the harlequin ladybird; Roy et al. 2016), and could damage non-target plants or restrict their establishment (Iannone & Galatowitsch 2008). Introductions should not be carried out without thorough assessment of likely negative impacts, non-target effects and effectiveness of control.
To be summarized as evidence for this action, studies must have successfully introduced a biocontrol agent that persisted in the environment. The agent must have been introduced with a clear aim to control problematic plants.
For this action, “vegetation” refers to overall or non-target vegetation. Studies that only report responses of target problematic plants have not been summarized.
Related actions: Use grazing to control problematic plants.
Iannone B.V. III & Galatowitsch S.M. (2008) Altering light and soil N to limit Phalaris arundinacea reinvasion in sedge meadow restorations. Restoration Ecology, 16, 689–701.
Keane R.M. & Crawley M.J. (2002) Exotic plant invasions and the enemy release hypothesis. Trends in Ecology and Evolution, 17, 164–170.
Roy H.E., Brown P.M.J., Adriaens T. et al. (2016) The harlequin ladybird, Harmonia axyridis: global perspectives on invasion history and ecology. Biological Invasions, 18, 997–1044.
Supporting evidence from individual studies
A replicated, randomized, paired, controlled, before-and-after study in 2005–2008 in five wet meadows in South Dakota, USA (Bahm et al. 2014) found that controlling problematic plants by mowing, applying herbicide and planting native upland plants increased plant species richness and cover of unplanted native species. All plots were initially dominated by reed canarygrass Phalaris arundinacea (>80% cover). After 1–3 growing seasons, plant species richness was higher in treated than untreated plots in 19 of 21 comparisons (for which treated: 2–5 species/0.25 m2; untreated: 2 species/0.25 m2). Treated plots also had greater cover of unplanted native species in 17 of 21 comparisons (for which treated: 8–57%; untreated: 3–21%) and lower cover of reed canarygrass in 21 of 21 comparisons (treated: 1–66%; untreated: 91–93%). Methods: Forty 3 x 40 m plots were established across five canarygrass-invaded wet meadows (eight plots/meadow). Between autumn 2005 and spring 2006, thirty-five plots (seven random plots/meadow) were mown, sprayed with herbicide and planted with 14 native upland grasses and forbs (2–23% cover after 1–3 growing seasons). Subsequent targeted mowing of “noxious weeds” was also carried out. The study does not distinguish between the effects of these interventions. Vegetation was surveyed at the end of each growing season 2006–2008, in nine 0.25-m2 quadrats/plot.Study and other actions tested