Cut/mow herbaceous plants to maintain or restore disturbance: freshwater marshes

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Twenty studies evaluated the effects, on vegetation, of cutting/mowing to maintain or restore disturbance in freshwater marshes. There were four studies in Belgium, three of which took place in one wetland area so probably shared some experimental plots. There were two studies in each of the UK, the USA and Estonia. There was one study in each of seven other European countries, Japan, Mexico and Brazil. In 15 of the studies vegetation was measured at least six months after the last cut.

VEGETATION COMMUNITY

  • Community composition (6 studies): Four replicated, paired, controlled studies (two also randomized and before-and-after) of freshwater marshes and wet meadows in Belgium, Switzerland, Mexico and Estonia reported that the overall plant community composition differed between cut and uncut sites after 1–5 years, or typically diverged in cut and uncut areas over 3–10 years. One before-and-after study in a freshwater marsh in Belgium reported that the overall plant community composition changed over seven years after resuming annual mowing. One replicated, paired, controlled, before-and-after study in wet grasslands in Germany reported that over 20 years, mowing increased the average moisture preference of the vegetation.
  • Overall richness/diversity (11 studies): Seven studies (including two replicated, paired, controlled) in freshwater marshes in Belgium, the UK, Mexico and Estonia reported that cut marshes had higher plant species richness than uncut marshes. Two of these studies reported the same result for diversity. One before-and-after study in a freshwater marsh in Belgium reported that plant species richness increased over seven years after resuming annual mowing. Three replicated, paired, controlled studies in reedbeds in the UK and wet meadows in Germany and Estonia reported that cutting typically had no clear or significant effect on plant species richness, after 3–5 months or over 5–20 years. The two studies in the UK and Estonia found the same result for diversity.
  • Characteristic plant richness/diversity (1 study): One replicated, paired, controlled, before-and-after study in a temporary marsh in France reported that two years of annual autumn cutting increased the number of habitat-characteristic plant species present.

VEGETATION ABUNDANCE

  • Overall abundance (3 studies): Two replicated, controlled studies (one also randomized, paired, before-and-after) in freshwater marshes in the USA found that cutting had no significant effect on overall vegetation cover over 72 days or three years. One replicated, paired, controlled study in wet grasslands in Belgium reported that plots mown annually for two years contained less above-ground biomass, just before mowing, than unmown plots.
  • Herb abundance (1 study): One replicated, paired, controlled, before-and-after study in wet grasslands in Germany reported that mowing increased sedge cover over 20 years, but had no clear effect on cover of rushes, forbs, ferns, grasses and legumes.
  • Tree/shrub abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in a wet prairie in the USA found that cutting had no significant effect on woody plant cover: there were similar increases, over three years, in cut and uncut plots.
  • Bryophyte abundance (1 study): One replicated study in a freshwater marsh in Belgium reported that total moss cover increased over five years after resuming annual mowing.
  • Individual species abundance (15 studies): Fifteen studies quantified the effect of this action on the abundance of individual plant species. For example, five studies (including one replicated, randomized, paired, controlled) in freshwater marshes in Belgium, the UK and the Czech Republic reported that common reed Phragmites australis was more abundant in cut than uncut areas. Two studies (one site comparison, one before-and-after) in fresh/brackish marshes in Belgium and Denmark reported that cutting reduced common reed cover or density. The two studies in Belgium reported that cutting had no clear effect on common reed frequency. Four studies (including one replicated, randomized, paired, before-and-after) in freshwater marshes in the Netherlands, Switzerland, Japan and Italy found that the effect of cutting on common reed abundance depended on factors such as the year, plant community type, cutting season, cutting intensity and time since mowing.

VEGETATION STRUCTURE

  • Overall structure (1 study): One replicated, randomized, paired, controlled study in wet meadows in Switzerland reported that mown plots experienced a shift in vegetation cover towards lower vegetation layers, over 3–4 years, compared to a shift to upper layers in unmown plots.
  • Visual obstruction (1 study): One replicated, controlled study in a freshwater marsh in Belgium reported that summer-cut plots had lower horizontal vegetation cover than uncut plots (or winter-cut plots) over six years after resuming annual mowing.
  • Height (6 studies): Three replicated, controlled studies (one also randomized and paired) in freshwater marshes in Belgium, the UK and the USA reported that cut marshes had shorter vegetation than uncut marshes. This was true for vegetation overall, vegetation other than common reed Phragmites australis, and for common reed cut in winter or spring (but not summer). Two replicated, paired, controlled, before-and-after studies in a marsh in Mexico and wet grasslands in Germany reported that cutting/mowing had no significant or clear effect on vegetation height, after 12 months or over 20 years. One site comparison study in the Czech Republic found that common reed was taller, when measured in the summer, in a winter-mown reedbed than in an unmown reedbed.
  • Diameter/perimeter/area (5 studies): Two studies (one site comparison, one before-and-after) in fresh/brackish marshes in Belgium and Denmark reported that cutting, or time since last cutting, had no significant or clear effect on the stem diameter of common reed Phragmites australis. Two studies (including one replicated, randomized, paired, controlled) of reedbeds in the UK and the Czech Republic found that cut areas contained thicker reed stems than uncut areas, after one growing season. One replicated, randomized, paired, controlled, before-and-after study in wet meadows in Switzerland found that the effect of cutting on common reed shoot diameter depended on the plant community type and season of mowing.
  • Basal area (1 study): One site comparison study in a fresh/brackish marsh in Denmark found that the basal area of common reed Phragmites australis stems was smaller in a reedbed cut two years previously than in a reedbed cut seven years previously. Only “tall” stems were sampled.

OTHER

  • Survival (1 study): One replicated, randomized, paired, controlled study in a wet prairie in the USA found that mowing had no significant effect on woody plant survival over the following year.

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, paired, controlled study in 1972–1975 in a created reedbed in the Netherlands (van der Toorn & Mook 1982) reported mixed effects of winter mowing on the subsequent density of common reed Phragmites australis. Statistical significance was not assessed. In two of three comparisons (both in 1972), the maximum annual reed density was lower in mown plots (340–450 stems/m2) than in unmown plots (520–730 stems/m2). In the other comparison (in 1974), the maximum annual reed density was higher in a mown plot (470 stems/m2) than in an unmown plot (250 stems/m2). Methods: In 1971, two pairs of plots were established in a young reedbed (sown in 1968). One pair was in a wetter area (flooded spring to autumn). One pair was in a drier area (water table 30–100 cm below surface). Between 1972 and 1975, one plot/pair was mown each winter. The other plots were not mown. All standing reed stems were counted between April and October each year (0.25–0.50 m2 quadrats; 4–6 quadrats/plot/sampling date).

    Study and other actions tested
  2. A replicated, paired, controlled study in 1977–1982 in a freshwater marsh in Belgium (Gryseels 1989) reported that winter-mown plots developed a different plant community to unmown plots, typically with more plant species, higher cover of common reed Phragmites australis and lower cover of two weedy herb species. Statistical significance was not assessed. Over five years, mown and unmown plots contained distinct plant communities (data reported as a graphical analysis). More plant species were recorded in winter-mown plots than unmown plots in 25 of 25 comparisons (mown: 9–29 species/plot; unmown: 4–11 species/plot) – but a larger area was probably sampled in mown plots. The mown plots had higher common reed cover in 20 of 25 comparisons (for which mown: 55–90%; unmown: 25–86%), but lower cover of bindweed Calystegia sepium in 23 of 30 comparisons (for which mown: 5–67%; unmown: 27–84%) and lower cover of common nettle Urtica dioica in 25 of 25 comparisons (for which mown: 3–31%; unmown: 27–86%). Mowing had no clear effect on the frequency of each species (see original paper for data). Total moss cover increased in mown plots, from 0–9% after one annual mow to 18–58% after five annual mows (data for unmown plots not reported). Methods: Five pairs of plots  (each 200–300 m2) were established in areas of degraded, weed-invaded marsh (where “traditional management” had ceased, and which had been partially drained). Each winter between 1977/1978 and 1981/1982, one plot in each pair was mown. The other plots were not mown. Each summer between 1978 and 1982, plant species and their cover were recorded in 3–12 permanent quadrats/plot (quadrat size not reported). Some of the plots in this study may also have been used in (4), but this was not clearly reported.

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  3. A before-and-after study in 1978–1986 in a freshwater marsh in Belgium (Gryseels 1989) reported that following the reinstatement of summer mowing, the plant community composition changed, species richness increased and cover of dominant herbs decreased. Statistical significance was not assessed. Over eight years, the overall plant community composition in the mown plot changed (data reported as a graphical analysis). The plot contained 15 plant species before mowing, compared to 25 species after seven years of mowing. Typical wet meadow species were only present after mowing (not quantified). Over the same time period, cover of the dominant herb species decreased: common reed Phragmites australis from 82% to 30%, bindweed Calystegia sepium from 66% to 7%, purple small-reed Calamagrostis canescens from 51% to 24%, and common nettle Urtica dioica from 24% to 1%. However, only common nettle occurred in fewer quadrats after eight years of mowing than before (decline from 75% to 18%). Common reed and bindweed maintained near 100% frequency, and the frequency of purple small-reed increased from 18% to 75%. Methods: Each summer between 1979 and 1985, one 225-m2 plot in a degraded, reed-dominated marsh (where “traditional management” had ceased, and which had been partially drained) was mown (once or twice per year). Cuttings were removed. In July 1978–1982 and 1986 (before mowing when applicable), plant species and their cover were recorded in 12 permanent quadrats in the plot (quadrat size not reported). The plot in this study may also have been used in (4), but this was not clearly reported.

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  4. A replicated, controlled study in 1978–1984 in a freshwater marsh in Belgium (Decleer 1990) reported that cut plots consistently contained more plant species, less of two weedy herb species and shorter vegetation than uncut plots, but reported that other effects on vegetation depended on the season/frequency of cutting. Statistical significance was not assessed. After six years, cut plots contained 17–23 plant species (compared to only 6–11 species in uncut plots). Bindweed Calystegia sepium and common nettle Urtica dioica were less abundant in cut than uncut plots, whereas common reed Phragmites australis was more abundant in cut plots (data reported as abundance classes). In cut plots, vegetation other than common reed was only 58–93 cm tall (vs uncut: 111–135 cm). In winter-cut plots, common reed was only 84 cm tall (vs summer-cut: 128–154 cm; uncut: 130–154 cm). Summer-cut plots had only 57–62% horizontal vegetation cover (vs winter-cut: 95%; uncut: 80–99%). Summer-cut plots had 5% cover of bare ground (i.e. not covered by vegetation or litter; vs 0% in winter-cut and uncut plots). Methods: Ten 300-m2 plots were established in areas of degraded, weed-invaded marsh. Vegetation in the marsh was historically cut, but had not been since the 1950s. The marsh was also partially drained. Three plots were cut by hand: two plots once each winter (November–March) from 1977/1978, and one plot twice each summer (July and September) from 1978. The other seven plots were left uncut. Vegetation was surveyed in summer (May–August) 1984. Horizontal cover was measured by viewing vegetation against a vertical board. This study may have used the same plots as (2) and (3), but this was not clearly reported.

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  5. A replicated, randomized, paired, controlled study in 1983–1986 in two wet meadows in Switzerland (Buttler 1992) reported that resuming annual mowing affected plant community composition and shifted the vegetation cover into lower layers. Statistical significance was not assessed. Within each of the two studied community types, the overall plant community composition became less similar in mown and unmown plots over 3–4 years (partial data reported as a graphical analysis). Meanwhile, mown plots experienced a shift in vegetation cover towards lower layers, whilst vegetation cover in unmown plots shifted towards the upper layers. This was true for vegetation overall, and for the dominant species in each community (partial data reported, as number of times survey pins touched living vegetation). These community and structural responses were similar whether cutting was done in summer or winter. However, responses of other individual species (e.g. density, shoot diameter and biomass of common reed Phragmites australis) differed between community types and mowing seasons (see Action: Change season/timing of cutting/mowing and original paper). Methods: Three sets of three plots (each 121–169 m2) were established in two historically mown lakeside wet meadows, that had been abandoned for “many years”. One random plot/set received each treatment: winter mowing (from early 1983), late summer mowing (from 1983) or no mowing. Cuttings were removed. Vegetation was surveyed each summer 1983–1986 (before annual mowing, where applicable).

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  6. A replicated, paired, site comparison study in 1988 of reedbeds in 12 sites in England, UK (Cowie et al. 1992) found that cut reedbeds had a significantly higher density of reed stems than uncut reedbeds, but also had significantly greater plant species richness and diversity (data not reported). Of 42 common, non-reed plant species for which data were reported, 25 were significantly more frequent in cut reedbeds (present in 2–93% of samples) than in uncut reedbeds (in 0–44% of samples). Three species were significantly less frequent in cut reedbeds (in <1–10% of samples) than in uncut reedbeds (in 4–23% of samples). Methods: In July and August 1988, vegetation was surveyed in two adjacent reedbeds in each of 12 sites. One reedbed/site had been cut “regularly” for 20 years (cuttings were removed), with the other unmanaged (neither cut nor burned) for ≥3 years. Reed stems (both live and dead) were counted in twenty 0.25-m2 quadrats/reedbed. Plant species were recorded in each quarter of each quadrat.

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  7. A replicated, randomized, paired, controlled study in 1988 in a reedbed in England, UK (Cowie et al. 1992) found that cut plots contained more (but shorter and slightly thicker) reed stems than uncut plots after one growing season, but similar plant richness and diversity. After 3–5 months, cut plots contained a higher density of reed stems (720 stems/m2) than uncut plots (484 stems/m2). On average, reed stems were shorter but thicker in cut plots (148 cm tall; 3.7 mm diameter) than uncut plots (177 cm tall; 3.5 mm diameter). Cut and uncut plots had statistically similar plant species richness (data reported but units not clear) and diversity (data reported as a diversity index). Of 17 common, non-reed plant species for which data were reported, 12 were more frequent in cut plots than in uncut plots (statistical significance not assessed; see original paper for data). Methods: Five pair of 30 x 40 m plots were established in a reedbed that had not been managed for ≥10 years. In March 1988, one random plot/pair was cut. Cuttings were removed. The other plots were left unmanged. All plots were flooded from April 1988. Vegetation was surveyed in July and August 1988. Live and dead reed stems were counted, and plant species were recorded, in 0.25-m2 quadrats (number not clear). Forty live reed stems/plot were measured. This summary takes some contextual and methodological details from Ditlhogo et al. (1992).

    Additional Reference: Ditlhogo M.K.M., James R., Laurence B.R. & Sutherland W.J. (1992) The effects of conservation management of reed beds. I. The invertebrates. Journal of Applied Ecology, 29, 265–276.

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  8. A replicated, paired, controlled study in 1986–1988 in five wet grasslands in Belgium (Dumortier et al. 1996) reported that plots in which annual mowing continued contained less plant biomass than unmown plots after two years, and were more dominated by a single species but contained more plant species. Statistical significance was not assessed. After two years, mown plots contained less above-ground plant biomass (550 g/m2 standing vegetation; 710 g/m2 including litter) than unmown plots (770 g/m2 standing vegetation; 1,120 g/m2 including litter). Acute sedge Carex acuta comprised 92% of the standing vegetation biomass in mown plots, compared to only 65% in unmown plots. However, mown plots contained more plant species (17–20 species/6 m2) than unmown plots (16 species/6 m2). The exact nature of changes in biomass and species richness over time depended on the month in which mowing was carried out (see Action: Change season/timing of cutting/mowing). The study also reported data on the cover of some example individual plant species (see original paper). Methods: In spring 1986, seven 7 x 7 m plots were established in each of five adjacent wet grasslands (mown annually for the previous 10 years). From 1986, one plot/grassland was mown in each month between June and November. Cuttings were removed. In the other plot in each grassland, mowing was stopped. Vegetation was surveyed each summer between 1986 and 1988. Biomass was cut and collected from five 30 x 30 cm quadrats/plot/year, before any mowing in that year, then dried and weighed.

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  9. A site comparison study in 1994 of two reedbeds in a fresh/brackish wetland in Denmark (Kristiansen 1998) found that a recently cut reedbed supported a lower density of tall common reed Phragmites australis with a smaller basal area than a more mature reedbed, although reed diameter was similar in both areas. In a reedbed cut two years before measurement, tall common reed stems were less dense (217 stems/m2) than in a more mature reedbed, cut seven years before measurement (422 stems/m2). However, the diameter of these reed stems did not significantly differ between the reedbeds (recently cut: 2.9; more mature: 3.1 mm). Combining these metrics, tall reed stems occupied a smaller proportion of the more recently cut reedbed (1,497 mm2/m2) than the more mature reedbed (3,014 mm2/m2). Methods: In 1994, vegetation was surveyed around 14 points in each of two reedbeds: one last cut in 1992 and one last cut in 1987. The reedbeds had been commercially harvested for “many years” previously. Most points were around (but approximately 2 m from) greylag goose Anser anser nests. At each point, all reed stems >75 cm tall were counted in four 0.25-m2 quadrats. Twenty stems/quadrat were measured.

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  10. A site comparison study in 1996 of two adjacent reedbeds in the Czech Republic (Rolletschek et al. 2000) found that a mown reedbed contained more, taller and thicker common reed Phragmites australis shoots than an unmown reedbed. The mown reedbed contained 79 reed shoots/m2, compared to 49 shoots/m2 in the unmown reedbed (statistical significance not assessed). Reed shoots in the mown reedbed were significantly taller (mown: 256 cm; unmown: 171 cm) and thicker (mown: 7.1 mm; unmown: 6.0 mm). Methods: In August 1996, vegetation was surveyed in two reedbeds with comparable nutrient levels: one mown in the previous winter, and one that had not been mown. The reedbeds were flooded between mowing and measurement. Surveys involved measurements of 25 shoots/reedbed, and counts of shoots in five 1-m2 quadrats/reedbed.

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  11. A replicated, randomized, paired, controlled, before-and-after study in 1994–1997 in an ephemeral wet prairie in Oregon, USA (Clark & Wilson 2001) found that mowing did not significantly affect the overall vegetation cover, forb cover, cover of the dominant herb species, and woody plant cover or survival. Over three years, mown and unmown plots experienced similar proportional changes in overall vegetation cover (increase; mown: 60%; unmown: 31%), native forb cover (decrease; mown: 14%; unmown: 77%), non-native forb cover (increase; mown: 43%; unmown: 28%), cover of the dominant herb species, tussock grass Deschampsia cespitosa (mown: 1% decrease; unmown: 30% increase; see original paper for data on other individual plant species) and woody plant cover (increase; mown: 25%; unmown: 20%). Furthermore, woody plants had similar survival rates over one year in mown plots (88%) and unmown plots (83%). Methods: In 1994, five pairs of plots (each 56–140 m2) were established in a degraded, seasonally flooded prairie. Woody plants had grown over 200 years of fire suppression. One plot/pair was mown (herbs and woody vegetation; cuttings removed) in autumn 1994 and 1996. Vegetation was surveyed before (summer 1994) and after mowing. Survival of six tagged woody plants/plot was recorded in summer 1995. Cover of selected herb species was recorded in three 0.5-m2 quadrats/plot in summer 1997.

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  12. A replicated, paired, controlled, before-and-after study in 2001–2003 in an ephemeral freshwater wetland dominated by tall herbs in southern France (Félisiak et al. 2004) reported that cutting the vegetation increased the number of plant species characteristic of Mediterranean temporary marshes. Statistical significance was not assessed. The number of characteristic plant species increased in cut plots, from 2–3 in the year before intervention to 6–12 in the two years after (units not reported). The number of characteristic plant species was relatively stable in unmanaged plots (before: 2–4; after: 3–6). Methods: Six pairs of plots were established near a reservoir, in an ephemerally flooded wetland where historical grazing had ceased. The plots were dominated by compact rush Juncus conglomeratus or bulrush Scirpus holoschoenus. In autumn 2001 and 2002, the vegetation was cut in one plot/pair. Cuttings were removed. Plant species were recorded in the year before intervention (2001) and for two years after (2002 and 2003).

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  13. A replicated, controlled, before-and-after study in 2000–2001 of a riparian reedbed near Tokyo, Japan (Asaeda et al. 2006) found that one summer cut reduced common reed Phragmites australis abundance in the first growing season, and reduced biomass but increased density in the second growing season. Before cutting, common reed abundance was statistically similar in all plots (above-ground biomass: 40–690 g/m2; density: 91–102 shoots/m2). In the first 3–4 months after cutting, reed abundance was lower in cut plots (biomass: 0–230 g/m2; density: 0–73 g/m2) than uncut plots (biomass: 690–1,010 g/m2; density: 103–113 shoots/m2). In the second growing season after cutting, reed biomass was lower in cut plots in 6 of 14 comparisons (for which cut: 260–910 g/m2; uncut: 520–1,040 g/m2; other comparisons no significant difference). In contrast, reed density was higher in cut plots in 12 of 12 comparisons (cut: 140–218 shoots/m2; uncut: 86–134 shoots/m2; statistical significance not assessed). Methods: In April 2000, three 6 x 10 m plots were established in a riparian reedbed. The site had been undisturbed for at least 10 years. Reeds were cut, 20–30 cm above ground level, from two of the plots (one in June 2000, one in July 2000). Cuttings were removed. The other plot was left undisturbed. Reed shoots were cut, counted, dried and weighed every 1–2 months between April and December 2000 and 2001 (three 0.125-m2 quadrats/plot/survey).

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  14. A replicated, randomized, paired, controlled, before-and-after study in 2006–2007 in a freshwater marsh in central Mexico (Hall et al. 2008) found that resuming cutting altered the plant community composition and increased plant richness and diversity, but had no lasting effect on dominance, height or density of southern cattail Typha domingensis. After one year, the overall plant community composition significantly differed between cut and uncut plots (data not reported). Cut plots had higher plant species richness (12.4–14.8 species/4 m2) than uncut plots (11.0 species/4 m2) and had greater plant diversity (data reported as a diversity index). In contrast, cut and uncut plots contained a similar relative abundance of southern cattail (data not reported) with similar height (harvested: 164–291; abandoned: 178–299 cm) and shoot density (harvested: 4–20; abandoned: 5–25 ramets/m2). Before intervention, community composition, richness, diversity, cattail height and cattail density were similar in all plots (richness: 8.8–9.9 species/4 m2; other data not reported). Methods: In May 2006, thirty-two 3 x 7 m plots were established in a degraded marsh (historically harvested and grazed, but both activities “minimal” since 2002). The plots were split across two areas with different water levels. In 24 random plots (12 plots/area), vegetation was cut to 20 cm above the soil surface. In 16 of these plots, cattail was cut for up to five months afterwards. All cuttings were removed. The final eight plots (4 plots/area) were not cut. Plant species, plant cover and cattail height were recorded before (May 2006) and one year after (May 2007) the initial cut, in four 1-m2 quadrats/plot.

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  15. A replicated, paired, controlled, before-and-after study in 1987–2007 in three wet grasslands in northwest Germany (Poptcheva et al. 2009) reported that plots mown twice each year experienced similar vegetation changes to unmown plots, with the exception of sedge abundance, species richness and community moisture value. Statistical significance was not assessed. Over 20 years, mown plots experienced increases in sedge cover, plant species richness, and the average moisture preference of the vegetation. In contrast, these metrics decreased in unmown plots. Other changes over time were similar (in direction if not in magnitude) in both mown and unmown plots. There were increases in rush cover, tall forb cover, fern cover and vegetation height. There were decreases in cover of grasses, legumes and short forbs. All data were reported as graphical analyses. Methods: From 1987, one plot (200–250 m2) in each of three wet grassland sites was mown (in June/July and September each year). One additional plot in each site was not mown. These sites had non-peaty soils, and had been maintained as fertilized pasture (one also mown) prior to the study. Trees and shrubs were removed from all plots throughout the study. Vegetation was surveyed in mid-June, every one or two years, between 1987 and 2007.

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  16. A replicated, paired, controlled, before-and-after study in 2000–2010 of three wet meadows in Estonia (Metsoja et al. 2012) found that annual mowing typically affected the overall plant community composition, but had no significant effect on plant richness or diversity. In three of five cases, mown plots had a significantly different overall plant community composition to unmown plots after 5–10 years, despite having a similar community composition before mowing began (data reported as graphical analyses). In ≥5 of 7 comparisons, mown and unmown plots had statistically similar plant species richness (mown: 2.1-7.0; unmown: 2.0-6.0 species/m2) and diversity (data reported as a diversity index). Before intervention, plots destined for each treatment had statistically similar richness and diversity in seven of seven comparisons. Mowing also had no clear effect on the proportion of grass-like plants in five of seven comparisons (similar change or lack of change over time in mown and unmown plots; see original paper for data). Methods: The study used three floodplain wet meadows that had been abandoned since the mid-1980s. From 2000 (two meadows) or 2005 (one meadow), parts of each meadow were mown each summer. Cuttings were typically not removed. Other parts were left unmown. Vascular plants were surveyed in the summer before mowing (2000) and after 5–10 years of mowing (2010), in 1-m2 quadrats in 2–3 plant community types/meadow.

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  17. A replicated, controlled study in 2005 in a freshwater marsh in southern Brazil (Silveira et al. 2012) reported that cutting southern cattail Typha domingensis reduced its density and biomass for <60 days. After 1–26 days, cut plots contained fewer mature cattail stems than uncut plots (cut: 05; uncut: 1944 stems/m2) and less above-ground cattail biomass (cut: 50–70; uncut: 350–470 g/m2). After 60–182 days, cut and uncut plots contained a statistically similar number of mature stems (cut: 1623; uncut: 1629 stems/m2) and above-ground biomass (cut: 230420; uncut: 300–440 g/m2). The density of young stems and dead stems never significantly differed between cut and uncut plots (see original paper for data). Methods: In June 2005, eight 1-m2 plots were established in a dense stand of southern cattail. Four plots were cut. Cuttings were removed. Four plots were left uncut. All cattail stems (mature: >80 cm tall; young: <80 cm tall; dead) were counted and measured in each plot until December 2005. Dry, above-ground biomass was estimated from stem heights.

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  18. A replicated, site comparison study in 2009–2010 of a lakeshore marsh in Estonia (Palmik et al. 2013) reported that mown areas had higher plant species richness than unmown areas. Statistical significance was not assessed. Vegetation was surveyed in July/August, in the band of intermittently flooded wetland vegetation around the lake. There were 12.3 plant species/0.25 m2 in areas mown earlier that summer vs 5.9 plant species/0.25 m2 in areas not yet mown that summer. Methods: In July/August 2009 and 2010, plant species were recorded in 0.25-m2 quadrats, along nine transects on the edge of Lake Peipsi. This summary focuses on quadrats (number not clear) in the intermittently flooded zone between open water and upland terraces. The lakeshore had been reprofiled and cleared of undesirable tall vegetation (mostly common reed Phragmites austalis and willows Salix spp.) 1–17 years previously, and regularly mowed (in summer) since.

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  19. A paired, controlled, before-and-after study in 2000–2002 in two lakeshore reedbeds in northern Italy (Fogli et al. 2014) found that plots where mowing had been resumed typically had similar common reed Phragmites australis biomass to plots that remained unmown. After two years of resumed mowing, above-ground reed biomass was statistically similar in mown and unmown plots in three of four comparisons (for which mown: 370–1,751 g/m2; unmown: 375–1844 g/m2). In the other comparison, reed biomass was lower in plots mown twice each year (1,153 g/m2) than in unmown plots (1,844 g/m2). Before mowing, reed biomass was statistically similar in plots destined for each treatment (477–982 g/m2). Methods: In July 2000, three 10 x 10 m plots were established in each of two reedbeds on the shore of Lago di Aslerio. The reedbeds had been historically mown in winter (and sometimes in summer), but not for >30 years. From summer 2000, one plot/reedbed was mown once each year (August 2000 and 2001), one plot/reedbed was mown twice each year (February 2001 and 2002, plus August mowing), and one plot/reedbed was left unmown. Above-ground biomass was calculated from counts and measurements of reed shoots from three 1-m2 quadrats/plot, before intervention (July 2000) and two years later (July 2002).

    Study and other actions tested
  20. A replicated, controlled study in 2010 in a permanent freshwater marsh in Florida, USA (Venne et al. 2016) found that cut plots contained shorter vegetation than uncut plots, but had similar overall vegetation cover and contained a similar amount of surface-encrusting algae. Over 72 days following intervention, emergent vegetation was shorter in cut than uncut plots. This was true for both the average height (cut: 83 cm; uncut: 165 cm) and maximum height (cut: 101 cm; uncut: 200 cm). Plots under each treatment had statistically similar overall vegetation cover (cut: 28%; uncut: 41%), cover of surface-encrusting algae (cut: 14%; uncut: 21%) and biomass of surface-encrusting algae (cut: 13 g/m2; uncut: 42 g/m2). Methods: In early April 2010, eight 100-m2 plots were established in a marsh dominated by sawgrass Cladium mariscus ssp. jamaicense. Historically, this type of marsh was frequently disturbed by lightning fires. Four plots were cut with hedge trimmers, approximately 48 cm above marsh surface (32 cm above water). Cuttings were removed. The other four plots were not cut. Plants and algae were surveyed every 10 days, between 2 and 72 days after cutting. Algae were dried before weighing.

    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.

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Marsh and Swamp Conservation

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Marsh and Swamp Conservation
Marsh and Swamp Conservation

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