Introduce organisms to control problematic plants: freshwater swamps

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 swamps. The study was in the USA. It involved introducing plants to compete with problematic plants.


  • Overall richness/diversity (1 study): One replicated, randomized, controlled study in a petunia-invaded floodplain swamp in the USA found that plots planted with wetland herbs had greater overall plant species richness than unplanted plots, over the year after planting.
  • Native/non-target richness/diversity (1 study): The same study found that planted plots had greater native plant species richness than unplanted plots, over the year after planting.




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, controlled study in 2013–2014 in a floodplain swamp invaded by Mexican petunia Ruellia simplex in Florida, USA (Smith et al. 2016) found that amongst plots sprayed with herbicide, planting native wetland herb species increased plant species richness. Four herb species were planted, with survival rates of 2–57% after one year. Over this year, planted plots had higher plant species richness (total: 5.2; native: 3.8 species/2.25 m2) than unplanted plots (total: 1.8; native: 0.6 species/2.25 m2). However, planted and unplanted plots contained a statistically similar amount of Mexican petunia. This was true for density (planted: 8–31 stems/0.56 m2; unplanted: 5–35 stems/0.56 m2), cover (planted: 39%; unplanted: 55%) and, after 12 months, biomass (planted: 4 g/m2; unplanted: 8 g/m2). Methods: Fourteen 1.5 x 1.5 m plots were established in a floodplain swamp, where invasive Mexican petunia had been controlled (but not eradicated) with herbicide. In November 2013, seven random plots were planted with greenhouse-reared herbs (four species; four plants/species/plot; individual plants 30 cm apart). The other seven plots were not planted. Vegetation was surveyed for one year after planting.

    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?

List of journals searched by synopsis

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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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