Use cutting/mowing to control problematic herbaceous plants: freshwater swamps

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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How is the evidence assessed?

Effectiveness

40%
Certainty

34%
Harms

10%

Calculating overall effectiveness category

Background information and definitions

Cutting or mowing refers to the removal of above-ground parts of herbaceous plants or young trees/shrubs. Roots are left in place. Mowing and cutting can be broad tools affecting all plants in a community, or targeted at specific problematic plants. Whilst cutting may not kill the targeted plants, it may weaken them and may provide desirable plants with an opportunity to grow and outcompete problematic plants. The cut plant material could be left on site or removed and used for construction or energy production, for example (Lishawa et al. 2015). Caution: Mowing with heavy machinery could damage wetland soil and vegetation. Cutting by hand or with specialized vehicles might cause less damage.

This action includes evidence for all forms of cutting/mowing to control problematic plants, but bear in mind that the effects might be highly dependent on how the cutting/mowing is carried out (e.g. extent, timing, frequency, duration, and whether cuttings are left in place or removed) and site conditions (e.g. nutrient availability and water levels) (Rolletschek et al. 2000; Weltzin et al. 2005; Russell & Kraaij 2008; Fogli et al. 2014).

For this action, “vegetation” refers to overall or non-target vegetation. Studies that only report responses of target problematic plants have not been summarized.

^{Fogli S., Brancaleoni L., Lambertini C. & Gerdol R. (2014) Mowing regime has different effects on reed stands in relation to habitat. Journal of Environmental Management, 134, 56–62.}

^{Lishawa S.C., Lawrence B.A., Albert D.A. & Tuchman N.C. (2015) Biomass harvest of invasive Typha promotes plant diversity in a Great Lakes coastal wetland. Restoration Ecology, 23, 228–237.}

^{Rolletschek H., Rolletschek A., Hartzendorf T. & Kohl J. (2000) Physiological consequences of mowing and burning of Phragmites australis stands for rhizome ventilation and amino acid metabolism. Wetlands Ecology and Management, 8, 425–433.}

^{Russell I.A. & Kraaij T. (2008) Effects of cutting Phragmites australis along an inundation gradient, with implications for managing reed encroachment in a South African estuarine lake system. Wetlands Ecology and Management, 16, 383–393.}

^{Weltzin J.F., Keller J.K., Bridgham S.D., Pastor J., Allen P.B. & Chen J. (2005) Litter controls plant community composition in a northern fen. Oikos, 110, 537–546.}

Study locations

Key messages

Two studies evaluated the effects, on vegetation, of cutting/mowing problematic herbaceous plants or small shrubs in freshwater swamps. Both studies were in the USA.

VEGETATION COMMUNITY

Overall richness/diversity (1 study): One replicated, controlled study aiming to restore a swamp in the USA found that mowing canarygrass-invaded vegetation before spraying it with herbicide had no significant effect on overall plant richness or diversity, two growing seasons later, compared to spraying alone.
Native/non-target richness/diversity (1 study): The same study found that mowing canarygrass-invaded vegetation before spraying it with herbicide had no significant effect on native plant species richness, two growing seasons later, compared to spraying alone.

VEGETATION ABUNDANCE

Tree/shrub abundance (2 studies): Two replicated, controlled studies in the USA evaluated the effects, on tree/shrub abundance, of managing canarygrass-invaded vegetation by cutting. One study found that mowing canarygrass-invaded vegetation before spraying it with herbicide had no significant effect on the density of non-planted tree seedlings, two growing seasons later, compared to spraying alone. The other studyfound that managed plots (cut, disked and sprayed with herbicide) contained more non-planted tree seedlings than unmanaged plots, after 1–3 years.
Native/non-target abundance (1 study): One replicated, controlled study aiming to restore a swamp in the USA found that plots in which canarygrass-invaded vegetation was managed (by cutting, along with disking and applying herbicide) contained at least as much non-canarygrass herb cover, after 1–3 years, to plots in which vegetation was not managed.
Individual species abundance (1 study): One replicated, controlled study aiming to restore a swamp in the USA reported that mowing canarygrass-invaded vegetation before spraying it with herbicide affected the abundance of some individual plant species two growing seasons later.

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, controlled study in 2002–2004 aiming to restore a swamp in a reed canarygrass Phalaris arundinacea stand in Wisconsin, USA (Hovick & Reinartz 2007) reported that mowing before spraying herbicide affected the abundance of some individual plant species compared to spraying alone, but found no additional effect on plant diversity, plant richness, or the number of tree seedlings. After two growing seasons, overall plant diversity did not significantly differ between mown/sprayed plots and plots that had only been sprayed (data reported as a diversity index). The same was true for overall plant richness (mown/sprayed: 8.4; sprayed: 6.6 species/m²), native plant richness (mown/sprayed: 5.7; sprayed: 4.0 species/m²) or density of non-planted tree seedlings (mown/sprayed: 46; sprayed: 25 seedlings/m²). However, the study did report differences between treatments in the abundance of some individual plant species (statistical significance not assessed). For example, eastern common ragweed Ambrosia artemisiifolia was more abundant in mown/sprayed plots (20% of quadrats; 33% cover) than sprayed plots (0% of quadrats). Reed canarygrass was less abundant in mown/sprayed plots (80% of quadrats; 31% cover) than sprayed plots (100% of quadrats; 73% cover). Methods: Twenty plots were established in a canarygrass-invaded wetland. Twelve plots were mown in August 2002. All 20 plots were then sprayed with herbicide (Roundup®) in November 2002, and planted with tree/shrub seedlings (roughly 1 seedling/m²) in spring 2003. In August 2004, plant species and their cover were surveyed in ten 1-m² quadrats/treatment, ignoring planted trees/shrubs.
Study and other actions tested
Referenced paper
Hovick S.M. & Reinartz J.A. (2007) Restoring forest in wetlands dominated by reed canarygrass: the effects of pre-planting treatments on early survival of planted stock. Wetlands, 27, 24-39.
A replicated, controlled study in 2006–2009 in a floodplain swamp clearing invaded by reed canarygrass Phalaris arundinacea in Wisconsin, USA (Thomsen et al. 2012) found that cutting, disking and applying herbicide to invaded plots increased tree seedling abundance after 1–3 years, and increased cover of herbs other than canarygrass after three years. In three of three years following intervention, treated plots contained more tree seedlings (4–44 seedlings/m²) than untreated plots (0–5 seedlings/m²). At the same time, treated plots had lower reed canarygrass cover (7–31%) than untreated plots (83–92%). Cover of herbs other than reed canarygrass did not significantly differ between treated and untreated plots in the first two years after intervention (treated: 15–47%; untreated: 16–22%), but was higher in treated than untreated plots in the third year (treated: 35–58%; untreated: 12%). Methods: In November 2006, twenty plots (roughly 810 m²) were established in a storm-created clearing within a floodplain swamp. Sixteen canarygrass-dominated plots were treated by cutting the vegetation (with a mechanical mulcher), disking the soil, and applying herbicide (four combinations of herbicide type and dose; repeated applications in summer and autumn until November 2008). The other four plots received none of these interventions. The study does not distinguish between the effects of cutting, disking and applying herbicide. Some tree species were planted and/or sown across the whole clearing. Vegetation (excluding planted trees) was surveyed in August 2007–2009, in four 2.25-m² quadrats/plot.
Study and other actions tested
Referenced paper
Thomsen M., Brownell K., Groshek M. & Kirsch E. (2012) Control of reed canarygrass promotes wetland herb and tree seedling establishment in an Upper Mississippi River floodplain forest. Wetlands, 32, 543-555.

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

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

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