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

Overall effectiveness category Likely to be beneficial
Number of studies: 8
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How is the evidence assessed?

Effectiveness

55%
Certainty

55%
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

Eight studies evaluated the effects, on vegetation, of cutting/mowing problematic herbaceous plants or small shrubs in freshwater marshes. Six studies were in the USA, one was in Mexico and one was in Canada.

VEGETATION COMMUNITY

Community composition (1 study): One replicated, randomized, paired, controlled, before-and-after study in a cattail-dominated marsh in the USA found that cutting altered the overall plant community composition over the following two years.
Relative abundance (1 study): One replicated, randomized, paired, controlled study in a grass-invaded marsh in Mexico found that cut and uncut plots supported a similar relative abundance of six common plant species after 4–8 months.
Overall richness/diversity (4 studies): Two replicated, randomized, paired, controlled studies in invaded marshes/wet meadows in the USA found that cut plots typically had greater overall plant species richness and/or diversity than uncut plots, after 1–3 growing seasons. One of the studies carried out other interventions along with cutting. Two replicated, controlled studies in freshwater marshes in the USA and Mexico found that cut and uncut plots had similar overall plant richness and/or diversity, after 1–2 growing seasons.
Native/non-target richness/diversity (2 studies): One controlled, before-and-after study in a reed-dominated freshwater marsh in the USA found that cutting/mowing (along with applying herbicide) increased non-reed species richness three years later. One replicated, controlled, before-and-after study in cattail-invaded marshes in the USA found that mown and unmown marshes had similar native plant species richness after 1–12 months

VEGETATION ABUNDANCE

Overall abundance (3 studies): Two replicated, controlled studies in freshwater marshes in the USA and Mexico found that cut and uncut plots contained a similar amount of vegetation after 1–2 growing seasons. This was true for cover of wetland plants and density of all plants. One replicated, randomized, paired, controlled, before-and-after study in iris-invaded lakeshore marshes in Canada reported that cutting reduced overall vegetation cover, one year later, in a permanently flooded marsh but had no clear effect on cover in an intermittently flooded marsh.
Herb abundance (1 study): One replicated, randomized, paired, controlled study in a cattail-invaded wet meadow in the USA found that plots in which cattail was cut four times over two growing seasons developed greater cover of sedges Carex than uncut plots, but that cutting cattail only twice had no significant effect on sedge cover.
Native/non-target abundance (3 studies): Two controlled studies (one also replicated, randomized, paired; one also before-and-after) in reed- or canarygrass-dominated wetlands in the USA found that cut plots typically contained more native or non-target vegetation than uncut plots, after 1–3 growing seasons. Both studies carried out other interventions along with cutting. One replicated, controlled, before-and-after study in cattail-invaded marshes in the USA found that mown and unmown marshes supported a similar native vegetation density after 1–12 months, and similar native vegetation biomass after 12 months.
Individual species abundance (2 studies): Three studies quantified the effect of this action on the abundance of individual plant species, other than the species being controlled. For example, one replicated, randomized, paired, controlled study in a grass-invaded marsh in Mexico found that five of five monitored native species had similar cover in cut and uncut plots after 4–8 months.

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 1993–1995 in five freshwater marshes undergoing restoration in New York State, USA (Brown & Bedford 1997) found that mowing typically had no significant effect on richness or total cover of wetland plants, and cover of cattails Typha spp. Over two years after intervention, mown and unmown plots contained a statistically similar number of wetland plant species in six of six comparisons (mown: 1.9–4.5; unmown: 1.4–4.7 species/plot). Mown and unmown plots had statistically similar cover of wetland plants in five of six comparisons (for which mown: 10–107%; unmown: 5–96%; other comparison higher in mown plots). After two years, mown and unmown plots had statistically similar cattail cover in three of three comparisons (mown: 2%; unmown: 0–7%). Methods: The study used five degraded wetland sites, drained for ≥40 years. In summer 1993, areas within three sites were mown. Cuttings were not removed. In autumn 1993, all five sites were rewetted. Plant species and cover were recorded in 1994 and 1995 (precise date not reported), in 30 quadrats in the mown areas and 39 quadrats in nearby unmown areas. Quadrats spanned a range of elevations.
Study and other actions tested
Referenced paper
Brown S.C. & Bedford B.L. (1997) Restoration of wetland vegetation with transplanted wetland soil: an experimental study. Wetlands, 17, 424-437.
A controlled, before-and-after study in 1995–1998 in a freshwater marsh dominated by common reed Phragmites australis in Connecticut, USA (Farnsworth & Meyerson 1999) found that cutting/mowing the vegetation (along with applying herbicide) increased the evenness of the plant community and the abundance and richness of non-reed species. After three years, treated plots contained a more even plant community, less dominated by one or two species, than an untreated plot (data reported as a coefficient of variation; see original paper for data on individual species abundance). Treated plots also had greater plant species richness (cut/herbicide: 5; mow/herbicide: 7; untreated: 3 species/m², excluding common reed) and contained a greater density of non-reed stems (cut/herbicide: 78; mow/herbicide: 97; untreated: 15 stems/m²). Common reed was less abundant in treated plots, in terms of stem density (cut/herbicide: 19; mow/herbicide: 6; untreated: 36 stems/m²) and frequency (cut/herbicide: 64%; mow/herbicide: 45%; untreated: 98% of surveyed quadrats contained common reed). Before intervention, all plots had relatively similar plant species richness (2–3 species/m², excluding common reed), non-reed density (7–23 stems/m²) and reed density (33–40 stems/m²). Methods: In 1995, two 0.4-ha plots were treated in a reed-dominated, tidal, freshwater marsh. In August, each plot was sprayed with herbicide (Rodeo® 1%). In autumn, one plot was cut by hand and one was mown mechanically; cuttings were left in place. A third adjacent plot was neither sprayed with herbicide nor cut/mown. The study does not distinguish between the effects of cutting/mowing and applying herbicide. In late summer before (1995) and after (1996–1998) intervention, plant stems were identified and counted in fifty 1-m² quadrats/plot.
Study and other actions tested
Referenced paper
Farnsworth E.J. & Meyerson L.A. (1999) Species composition and inter-annual dynamics of a freshwater tidal plant community following removal of the invasive grass, Phragmites australis. Biological Invasions, 1, 115-127.
A replicated, randomized, paired, controlled study in a freshwater marsh invaded by antelope grass Echinochloa pyramidalis in eastern Mexico (López Rosas et al. 2006) found that cutting the vegetation had no significant effect on overall plant density, richness or diversity, the relative abundance of common plant species, or the absolute abundance of common native plant species. After 4–8 months, cut and uncut plots contained a statistically similar overall plant density (six of six comparisons; cut: 56–126; uncut: 54–93 plants/0.49 m²), species richness (six of six comparisons; cut: 4–8; uncut: 3–5 species/0.49 m²) and diversity (two of two comparisons; data reported as a diversity index). Accordingly, all six monitored plant species had a similar relative abundance in cut and uncut plots (five native species, plus antelope grass; see original paper for data). The five native plant species had statistically similar cover in cut and uncut plots in 14 of 14 comparisons (both treatments: 0–19% cover/species). In contrast, antelope grass had lower cover in cut plots in five of six comparisons (for which cut: 38–92%; uncut: 94–100%). Methods: In January (year not reported), twenty-one 0.49-m² plots were established (in seven sets of three) in a degraded marsh, invaded by antelope grass. In 14 plots (two random plots/set), vegetation was clipped to ground level. In seven of these, the most abundant native plant species was deliberately not clipped. In the final seven plots (one random plot/set), no vegetation was clipped. All 21 plots were enclosed, underground, by a plastic barrier. Vegetation was surveyed between May and September later that year (relative biomass in September only).
Study and other actions tested
Referenced paper
López Rosas H., Moreno-Casasola P. & Mendelssohn I.A. (2006) Effects of experimental disturbances on a tropical freshwater marsh invaded by the African grass Echinochloa pyramidalis. Wetlands, 26, 593-604.
A replicated, randomized, paired, controlled study in 2006–2008 in a wet meadow being invaded by hybrid cattail Typha x glauca in Wisconsin, USA (4) found that cutting cattail four times over two growing seasons increased cover of sedges Carex spp., but that cutting twice had no significant effect. After two growing seasons, sedge cover was higher in plots where cattails had been cut four times (33–66%) than in uncut plots (11–38%). However, plots where cattails had only been cut twice had statistically similar sedge cover (20–59%) to the uncut plots. Additional plots where all vegetation had been cut one month before sampling had 4–9% sedge cover. No sedge seedlings were found in any plot. Methods: Thirty-two 4 x 8 m plots were established (in two sets of 16) on the boundary between native wet meadow vegetation and a patch of hybrid cattail. In May 2006, all cattail stems were cut and removed from 24 plots (12 random plots/set). Eight of these plots (4 random plots/set) received each follow-up treatment over the next two growing seasons: cutting cattail four times upon regrowth to 1 m, cutting cattail twice upon regrowth to 1 m, or cutting all vegetation once in September 2007. The final eight plots (4 random plots/set) were never cut. Sedge cover was surveyed in October 2007, in four 1-m² quadrats/plot.
Study and other actions tested
Referenced paper
Hall S.J. & Zedler J.B. (2010) Constraints on sedge meadow self-restoration in urban wetlands. Restoration Ecology, 18, 671-680.
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, overall 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/set) were mown (15–25 cm height; cuttings removed), sprayed with herbicide and planted with 14 native upland species. 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
Referenced paper
Bahm M.A., Barnes T.G. & Jensen K.C. (2014) Evaluation of herbicides for control of reed canarygrass (Phalaris arundinacea). Natural Areas Journal, 34, 459-464.
A replicated, randomized, paired, controlled, before-and-after study in 2011–2013 in a freshwater marsh dominated by hybrid cattail Typha x glauca in Michigan, USA (Lishawa et al. 2015) found that cutting the cattail-dominated vegetation changed the plant community composition and increased plant species richness and diversity. In the two years following cutting, the overall plant community composition significantly differed between cut and uncut plots (data reported as a graphical analysis). After two years (but not one), cut plots contained more plant species than uncut plots (14 vs 8 species/16 m²) and had greater plant diversity (reported as a diversity index). At this time, hybrid cattail was also less dominant in cut than uncut plots (63 vs 87% of total cover). After one year (but not two), cut plots contained less above-ground cattail biomass than uncut plots (280 vs 700 g/m²). Before intervention, plots destined for each treatment contained statistically similar plant communities with similar species richness (5–7 species/16 m²), diversity, cattail relative cover (85–87%), and cattail biomass (data not reported). Methods: Sixteen 4-m² plots were established in two areas of a freshwater marsh that had been invaded by hybrid cattail (one for >30 years, one for <20 years). In August 2011, all vegetation was cut at ground level in eight plots (four random plots/area). Cuttings were removed. No vegetation was cut in the other eight plots. Roots and rhizomes (underground horizontal stems) were cut around the edge of each plot. Vegetation was surveyed in July before (2011) and for two years after (2012–2013) intervention. Above-ground dry biomass was estimated, after intervention only, from the height of cattail stems.
Study and other actions tested
Referenced paper
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: harvesting Typha promotes plant diversity. Restoration Ecology, 23, 228-237.
A replicated, controlled, before-and-after study in 2013–2014 in twelve artificial marshes invaded by hybrid cattail Typha x glauca in Michigan, USA (Lawrence et al. 2016) found that a single mow had no significant effect on native plant richness, density or biomass one year later. After one year, mown and unmown marshes had statistically similar native plant richness (mown: 1.8–4.5; not mown: 4–4.5 species/2 m²), density (mown: 190–560; not mown: 300 stems/m²) and above-ground biomass (mown: 160–180; not mown: 440 g/m²). The same was true for cattail density (mown: 17; not mown: 44 stems/m²) although above-ground cattail biomass was lower in mown plots (mown: 90; not mown: 750 g/m²). Most outcomes also did not significantly differ between treatments after one month, the exceptions being native plant biomass (mown: <10; not mown: 260 g/m²) and cattail density (mown: 5–6; not mown: 55 stems/m²). Before mowing, vegetation was statistically similar in marshes destined for each treatment (native richness: 2.7–4.3 species/2 m²; native density: 150–230 stems/m²; native biomass: 320–380 g/m²; cattail density: 63–69 stems/m²; cattail biomass: 1,080–1,130 g/m²). Methods: In July 2013, all vegetation was mown in eight experimental marshes (1 x 2 m area, 1 m soil depth). The marshes had been created in 2002 and planted (i.e. deliberately invaded) with hybrid cattail in 2004. Cuttings were left in four marshes but removed from the other four. Four additional marshes were not mown. Plant species, density and height were recorded in all marshes immediately before, one month after and one year after mowing. Above-ground dry biomass was calculated from height measurements.
Study and other actions tested
Referenced paper
Lawrence B.A., Lishawa S.C., Rodriguez Y. & Tuchman N.C. (2016) Herbicide management of invasive cattail (Typha × glauca) increases porewater nutrient concentrations. Wetlands Ecology and Management, 24, 457-467.
A replicated, randomized, paired, controlled, before-and-after study in 2014–2015 in two lakeshore marshes invaded by yellow flag iris Iris pseudacorus in British Columbia, Canada (Tarasoff et al. 2016) reported that the effect of cutting yellow flag iris on recolonizing vegetation depended on the water level. Statistical significance was not assessed. Before cutting, all study plots were completely covered by yellow flag iris. One year later, in the permanently flooded marsh, cut plots had only 5% vegetation cover (mixture of yellow flag iris seedlings and broadleaf cattail Typha latifolia; species cover not quantified) whilst uncut plots had 100% vegetation cover (yellow flag iris only). In the intermittently flooded marsh, both cut and uncut plots were completely covered by yellow flag iris. Methods: Nine pairs of plots (approximately 1 m²) were established in iris-dominated marshes on the shores of two lakes. In one random plot/pair, yellow flag iris was cut to 0–4 cm above the sediment. Cuttings were removed. The other plots were left uncut. Vegetation cover was surveyed in July 2015.
Study and other actions tested
Referenced paper
Tarasoff C.S., Streichert K., Gardner W., Heise B., Church J. & Pypker T.G. (2016) Assessing benthic barriers vs. aggressive cutting as effective yellow flag iris (Iris pseudacorus) control mechanisms. Invasive Plant Science and Management, 9, 229-234.

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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This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

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