Introduce organisms to control problematic plants: freshwater marshes

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One study evaluated the effects, on vegetation, of introducing organisms (other than large vertebrate grazers) to control problematic plants in freshwater marshes. The study was in the USA. It involved introducing plants to compete with problematic plants.


  • Overall richness/diversity (1 study): One replicated, randomized, paired, controlled study in canarygrass-invaded wet meadows in the USA found that plots planted with upland vegetation (after mowing and applying herbicide) had greater overall plant species richness than untreated plots, after 1–3 growing seasons.


  • Native/non-target abundance (1 study): One replicated, randomized, paired, controlled study in canarygrass-invaded wet meadows in the USA found that plots planted with upland vegetation (after mowing and applying herbicide) typically had greater cover of unplanted native vegetation than untreated plots, after 1–3 growing seasons.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. 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
Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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