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Providing evidence to improve practice

Action: Cut/mow herbaceous plants to maintain or restore disturbance Peatland Conservation

Key messages

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  • Fourteen studies evaluated the effects on peatland vegetation of cutting/mowing to maintain or restore disturbance. All 14 studies were in fens or fen meadows. Most studies examined the effect of annual mowing regimes, but three examined the effect of single cuts. N.B. Cutting/mowing in peatlands with no history of disturbance is considered as a separate action.
  • Plant community composition (7 studies): Six replicated studies in fens and fen meadows in the UK, Belgium, Germany and the Czech Republic reported that mowing altered the overall plant community composition (compared to no mowing, before mowing or grazing). One site comparison study in Poland reported that mowing a degraded fen (along with other interventions) made the plant community more similar to a target fen meadow.
  • Characteristic plants (5 studies): Four studies (including one replicated, paired, controlled, before-and-after) in fens and fen meadows in Switzerland, Germany, the Czech Republic and Poland found that cutting/mowing increased cover of fen- or wet meadow-characteristic plants. One replicated before-and-after study in fens in the UK found that a single mow typically had no effect on cover of fen-characteristic plants. In Poland and the UK, the effect of mowing was not separated from the effects of other interventions.
  • Moss cover (6 studies): Of six studies (five replicated, paired, controlled) in fens or fen meadows, four in Belgium, Switzerland and the Czech Republic found that mowing increased total moss or bryophyte cover. Two studies in Poland and the UK found that a single mow typically had no effect on bryophyte cover (total or hollow-adapted mosses).
  • Herb cover (8 studies): Six replicated studies (three also randomized and controlled) in fens and fen meadows in Belgium, Germany, Poland and the UK found that mowing reduced cover or abundance of at least one group of herbs (including bindweed, reeds, sedgespurple moor grass and grass-like plants overall). One before-and-after study in a fen in Poland found that mowing (along with other interventions) increased sedge cover. One replicated, randomized, paired, controlled study in fen meadows in Switzerland found that mowing had no effect on overall herb cover.
  • Tree/shrub cover (3 studies): Of three replicated studies in fens, two in the UK found that a single mow (sometimes along with other interventions) reduced shrub cover. However, one study in Poland found that a single mow had no effect on shrub cover.
  • Vegetation structure (7 studies): In the following studies, vegetation structure was measured 6–12 months after the most recent cut/mow. Three replicated studies in fens in Poland and the UK reported that a single mow (sometimes along with other interventions) had no, or no consistent, effect on vegetation height. One replicated, paired, site comparison study in fen meadows in Switzerland found that mowing reduced vegetation height. Three studies (including two replicated, paired, site comparisons) in fen meadows in Switzerland, Poland and Italy found mixed effects of mowing on vegetation biomass (total, sedge/rush, moss or common reed). One replicated, paired, site comparison study in Germany reported that mown fen meadows had similar vegetation structure to grazed meadows.
  • Overall plant richness/diversity (11 studies): Eight studies in fens and fen meadows in the UK, Belgium, Switzerland, Germany, the Czech Republic and Poland found that mowing/cutting increased plant species richness (compared to no mowing, before mowing or grazing). Three studies (including two replicated, randomized, paired, controlled) in fens in Poland and the UK found that a single mow (sometimes along with other interventions) typically had no effect on plant species richness and/or diversity.

Supporting evidence from individual studies

1 

A replicated before-and after study in 1980–1982 in a fen meadow in England, UK (Rowell et al. 1985) reported that after reinstating annual summer mowing, the plant community composition changed and species richness increased. These results are not based on tests of statistical significance. The overall composition of the plant community changed over two years of annual mowing (data reported as a graphical analysis). There were 1.1–2.3 plant species/250 cm2 before mowing, but 1.5–3.6 species/250 cm2 after two years of annual mowing. Amongst mown plots, species richness increased more in July-mown subplots than May-mown subplots, but community composition changes were similar (see Section 9.5). In 1980–1982, traditional annual summer mowing was reinstated in 10 plots across two fen meadow community types. In each plot, one random 25 m2 subplot was mown in May, one mown in July and one mown in May and July. Cuttings were removed. Immediately before each mowing, vascular plant species were recorded in sixteen 250 cm2 quadrats/subplot. Prior to the study, the meadow had been mown every 3 years (rather than every year).

2 

A replicated, paired, controlled study in 1977–1982 in a degraded fen in Belgium (Gryseels 1989) reported that resuming winter mowing changed plant community composition, increased species richness and bryophyte cover, and reduced cover of one of three dominant herb species. These results were not tested for statistical significance. Over five years, mown and unmown plots contained distinct plant communities (data reported as a graphical analysis). In mown plots, there were 15–18 species/plot after one mow but 14–24 species/plot after five years of mowing (unmown plots stable at 5–9 species/plot). Total bryophyte cover was 5–15% after one mow but 23–75% after five years (data for unmown plots not reported). Cover of bindweed Calystegia sepium declined in mown plots only (from 11–51% to 1–29%; unmown plots stable at 31–62% cover). Cover of purple small-reed Calamagrostis canescens and common reed Phragmites australis declined in both mown and unmown plots. Three pairs of 100–200 m2 plots were established in areas of partially drained, overgrown fen. Every winter between 1977/1978 and 1981/1982, one plot per pair was mown. The other plots were not mown. Each summer between 1978 and 1982, cover of every plant species was estimated in permanent quadrats (size and number not reported).

3 

A replicated before-and-after study in 1978–1986 in a degraded fen 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. These results were not tested for statistical significance. Over eight years, the overall plant community composition in mown plots changed (data reported as a graphical analysis). There were 12–15 plant species/plot before mowing but 23–32 species/plot after seven years of mowing. Cover of the dominant herb species decreased: common reed Phragmites australis in two of three plots (from 66–82% to 14–30%), purple small-reed Calamagrostis canescens in two of three plots (from 51–80% to 24–27%), bindweed Calystegia sepium in all three plots (from 17–66% to 3–18%). Each summer between 1979 and 1985, three plots (200–300 m2) in areas of partially drained, overgrown fen were mown once or twice. Cuttings were removed. Each summer between 1978 and 1986, cover of every plant species was estimated in permanent quadrats (size and number not reported).

4 

A replicated, paired, site comparison study in 1998 in 27 fen meadows in Switzerland (Diemer 2001) found that mown meadows had greater plant species richness and vegetation cover than abandoned meadows, but shorter vegetation with less biomass. Mown meadows contained more plant species than abandoned meadows (mown: 33; abandoned: 27 species/8 m2) and more fen-characteristic species (mown: 16; abandoned: 14 species/8 m2). Plant diversity was also higher in mown meadows (reported as a diversity index). Mown meadows had greater cover of total vegetation (mown: 84%; abandoned: 77%) and mosses (mown: 47%; abandoned: 30%). Vegetation was shorter in mown meadows (mown: 16; abandoned: 24 cm) and total vegetation biomass was lower (mown: 265; abandoned: 320 g/cm2). However, mown meadows contained greater sedge/rush biomass (mown: 146; abandoned: 102 g/cm2). In summer 1998, vegetation was studied in 27 fen meadows: seven mown (each autumn for at least 20 years) and twenty abandoned (not mown for 2–35 years). Each mown meadow was matched with nearby abandoned meadows. Plant species and cover were recorded in four 2 m2 plots/meadow. Above-ground biomass was cut in two 340 cm2 quadrats/plot, then dried and weighed.

5 

A replicated, randomized, controlled study in 1996–1998 in a degraded fen meadow in Germany (Jensen & Meyer 2001) found that repeatedly clipped plots contained more species-rich and diverse vegetation than unclipped plots, and had a different community with more fen-characteristic plants. Over three years, plant species richness was significantly higher in clipped plots (17–23 species/2 m2) than unclipped plots (15–18 species/2 m2). Plant diversity was also higher in clipped plots (data reported as a diversity index). Overall plant community composition was initially similar in all plots but diverged over time. In clipped plots, shorter herbaceous species characteristic of fens and wet meadows became more abundant, taller sedges and reeds less so (data reported as a graphical analysis; changes not tested for statistical significance). Twenty 2 m2 plots were established in an abandoned fen meadow. In ten random plots, vegetation was manually clipped (5–10 cm above the ground) every summer between 1996 and 1998. Ten plots were unclipped controls. Litter was removed from half of the plots in each treatment. Cover of every plant species was estimated annually, after clipping, in each plot.

6 

A replicated, paired, site comparison study in 32 fen meadows in southern Germany (Stammel et al. 2003) found that mown meadows contained a significantly different plant community and more plant species than grazed meadows, but there was no difference in vegetation height or biomass. Meadows mown or grazed for at least 10 years had different overall plant communities (data reported as a graphical analysis). Mown meadows contained more plant species than grazed meadows, per meadow (mown 79; grazed: 71 species) and per 25 m2 plot (mown: 51; grazed: 43 species), and more fen-characteristic species (mown: 19; grazed: 18 species/plot). Meadows did not differ significantly in vegetation height (mown: 24; grazed: 19 cm) or above-ground biomass (mown: 1,103; grazed: 954 g/m2). Of the 32 studied meadows, 16 were mown each autumn and 16 were open to cattle (<0.5/ha) each summer. In August (year not reported), cover of every plant species was recorded in 25 m2 plots: 51 across the mown meadows and 58 across the grazed meadows. Vegetation height was measured at three points in each meadow. Biomass was cut from three 25 x 25 cm quadrats then dried and weighed.

7 

A replicated, randomized, paired, controlled study in 1998–2000 in 15 degraded fen meadows in Switzerland (Billeter et al. 2007) found that resuming mowing increased plant species richness and bryophyte cover, but had no effect on other plant cover or biomass. After two years, species richness was higher in mown plots than unmown plots: of all plants (32 vs 28 species/2 m2) and fen-characteristic plants (18 vs 16 species/2 m2). Mown plots also had greater bryophyte cover than unmown plots (60 vs 47%). There were no significant differences in vascular plant cover (data not reported), total biomass (mown: 193; unmown: 225 g/m2) or herb biomass (mown: 52–80; unmown: 51–110 g/m2). Four 2 m2 plots were established in each meadow (abandoned for 4–35 years). In September 1998 and 1999, two random plots in each meadow were mown. Cuttings were removed. The other two plots were not mown. In summer 2000, vegetation cover was visually estimated in each plot. Above-ground biomass from a 20 x 20 cm subplot was cut, dried and weighed.

8 

A replicated, paired, controlled, before-and-after study in 2002–2007 in a degraded grassy fen in the Czech Republic (Hájkova et al. 2009) found that reinstating mowing changed plant community composition, increased vascular plant richness and increased bryophyte cover. In mown (but not unmown) plots, the overall plant community composition changed significantly over five years in favour of fen-characteristic plants (data reported as graphical analyses). Mown plots had higher vascular plant richness than unmown plots after four years (twice-mown: 16–18; once-mown: 13; unmown: 7–9 species/m2) and greater bryophyte cover after two years (twice-mown: 85–95%; once-mown: 64–89%; unmown: 7–13%). Before intervention, all plots had similar vascular plant richness (6–9 species/m2) and bryophyte cover (9–12%). Five blocks of three plots (2.5 x 2.5 m) were established in an abandoned fen, dominated by tall moor grass Molinia arundinacea. Between 2002 and 2007, one plot/block received each mowing treatment: none, mowing in September, or mowing in May and September. Each year before May mowing, cover of every plant species was estimated in a 1 m2 quadrat in the centre of each plot.

9 

A replicated, paired, site comparison study in 2005–2008 in a fen meadow in Poland (Opdekamp et al. 2012) found that mown plots contained more plant species and more moss biomass than unmown plots, but similar total plant biomass. Plant species richness was higher in plots mown every year (25 species/210 sample pins) than plots not mown for about 15 years (21 species/210 sample pins). The most abundant species under both treatments were sedges: black sedge Carex nigra in mown plots (16% cover) and fibrous tussock sedge Carex approprinquata in unmown plots (23% cover). Mown plots contained greater moss biomass than unmown plots, but total plant biomass was similar under both treatments (reported as statistical model results). Between 2005 and 2008, fifteen pairs of 2 x 2 m plots were sampled in early July. In each pair, one plot was in mown fen meadow (mown in late summer for at least 30 years). The other plot was in abandoned fen meadow, not mown for approximately 15 years. In each plot, plant species touching 210 pins were recorded. Live above-ground vegetation was collected from a 0.25 m2 quadrat, then dried and weighed.

10 

A before-and-after, site comparison study in 2004–2009 in a degraded fen in Poland (Kotowski et al. 2013) found that in an area where mowing was resumed (also cleared of shrubs and rewetted), the plant community composition changed in favour of fen meadow and wet meadow species. Over five years, the overall community composition became more similar to target fen meadow vegetation (data reported as a graphical analysis; change not tested for statistical significance). The abundance of fen meadow and wet meadow plant species, including sedges Carex spp., significantly increased in the managed area but did not change in the target area (data reported abundance indices). In 2004, annual late summer mowing was resumed in 0.7 ha of drained, overgrown fen. The area had been prepared by removing willow Salix cinerea shrubs, and was later rewetted. The study does not distinguish between the effects of these interventions. The managed area was compared to 0.9 ha of target, shrub-free, fen meadow vegetation (retained in depressions during the drained period, but also affected by the rewetting and mown every other year). Annually between 2004 (before intervention) and 2009, vegetation cover was estimated in 18–22 plots/area. Plots were 20 x 20 m.

11 

A replicated, randomized, paired, controlled study in 2009­–2011 in a degraded fen in Poland (Kotowski et al. 2013) found that mown and unmown plots had a similar total number of plant species, vegetation height, shrub cover and hollow-adapted moss cover after 1–2 years, but that mown plots had less cover of sedges Carex spp. (all data reported as standardised scores). Twelve pairs of plots were established in a historically drained, abandoned fen. In late summer 2009 or 2010, one random plot in each pair was mown using a modified snow groomer. The other plots were not disturbed. In 2011, cover of every plant species was estimated in 4 m2 quadrats (number not reported).

12 

A controlled, before-and-after study in 2000–2002 in a degraded fen meadow in Italy (Fogli et al. 2012) found that after reinstatement of mowing, the biomass of common reed Phragmites australis decreased. After two years of mowing, reed biomass was lower in a plot mown twice each year (22 g/m2) and a plot mown once each year (56 g/m2) than in an unmown plot (130 g/m2). Before intervention, reed biomass was similar in all plots (99–112 g/m2). In July 2000, three 10 x 10 m plots were established in an area of abandoned fen meadow invaded by reeds. Reed shoots were counted and measured in three 1 m2 quadrats/plot and reed biomass was calculated. Then, one plot was mown once each year (August 2000 and 2001), one was mown twice each year (February 2001 and 2002, plus August mowing), and one was not mown. In July 2002, biomass measurements were repeated.

13 

A replicated before-and-after study in 2010–2013 in two degraded fens in Wales, UK (Birch et al. 2015) found that mowing (sometimes along with other interventions) reduced shrub and grass/sedge/rush cover, typically had no effect on cover of fen-characteristic species and plant richness/diversity, and had mixed effects on vegetation height. In five of six managed plots, there were declines in shrub cover (before intervention: 27–87%; after 2–3 years: 9–19%) and total grass/sedge/rush cover (before: 91–98%; after: 63–80%). Cover of purple moor grass Molinia caerulea decreased in three plots (before: 64–81%; after: 3–34%). In four or five plots, there was no change in cover of fen-characteristic mosses (<1% before and after), fen-characteristic herbs (before: <2%; after: <1%), plant species richness (before: 9–17; after: 8–14 species/4 m2) or plant diversity (data reported as diversity indices). Management had mixed effects on vegetation height (increase: 1 plot; decrease: 2 plots; no change: 3 plots). Six 20 x 20 m plots were established across two abandoned fens. In autumn 2010 or spring 2011, each plot was mown once. Cuttings were removed. Four plots were also grazed. Two of these were also burned. The study does not distinguish between the effects of these interventions and mowing. Cover of every plant species was estimated before mowing (autumn 2010) and 2–3 years after (autumn 2012 or 2013), in five 4 m2 quadrats/plot.

14 

A replicated, randomized, paired, controlled, before-and-after study in 2011–2013 in three degraded fens in Wales, UK (Menichino et al. 2016) found that mowing typically reduced cover of grass-like plants and shrubs, typically had no effect on bryophyte cover, forb cover and plant species richness, and had mixed effects on vegetation height. In three of four comparisons, mown plots had less cover than unmown plots of grasses/sedges/rushes overall (50–56% vs 71–94%), the dominant sedge species (19–30% vs 41–82%), and shrubs (7–24% vs 11–36%). In contrast, in three of four comparisons mown and unmown plots had similar bryophyte cover (0–2%), forb cover (3–15% vs 2–20%) and plant species richness (6–17 species/plot vs 7–16 species/plot). Mown plots contained shorter vegetation than unmown plots in two of four comparisons (for which mown: 69–74 cm; unmown: 99–104 cm). Before mowing, all plots had similar vegetation cover, species richness and vegetation height. Seventeen pairs of 10 x 10 m plots were established across three abandoned fens. In spring 2012, one random plot in each pair was mown once (with a mechanical mower or strimmer; cuttings were removed). The other plots were left unmown. Data were recorded before mowing (summer 2011) and 1–2 years after (summer 2012 and 2013), in five 4 m2 quadrats/plot.

Referenced papers

Please cite as:

Taylor N.G., Grillas P. & Sutherland W.J. (2019) Peatland Conservation. Pages 375-438 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.