Introduce organisms to control problematic plants: freshwater swamps

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

54%
Certainty

24%
Harms

0%

Calculating overall effectiveness category

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.}

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.

VEGETATION COMMUNITY

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.

VEGETATION ABUNDANCE

VEGETATION STRUCTURE

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

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
Referenced paper
Smith A.M., Reinhardt Adams C., Wiese C. & Wilson S.B. (2016) Re-vegetation with native species does not control the invasive Ruellia simplex in a floodplain forest in Florida, USA. Applied Vegetation Science, 19, 20-30.

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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This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

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