Reduce frequency of cutting/mowing: freshwater marshes

Overall effectiveness category Likely to be beneficial
Number of studies: 4
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How is the evidence assessed?

Effectiveness

40%
Certainty

40%
Harms

0%

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Background information and definitions

This section considers the effects of different cutting/mowing frequencies, when the lower intensity may be suitable to conserve the target vegetation. Different plant species have differing tolerance to disturbance, so the frequency and intensity of disturbance can affect the plant community composition (Connell 1978).

To be summarized as evidence for this action, studies must have compared cutting/mowing at different frequencies (e.g. 1 vs 2 cuts/year) but with the same intensity and with at least some overlap in the timing of disturbance (e.g. summer vs summer + winter). For this action, “reduction” includes stopping disturbance altogether. However, studies comparing areas that remain uncut to areas that become cut, at any frequency, are not summarized as evidence for this action.

^{Connell, J.H. (1978) Diversity in tropical rain forests and coral reefs. Science, 199, 1302–1310.}

Study locations

Key messages

Four studies evaluated the effects, on vegetation, of reducing the frequency of cutting/mowing in freshwater marshes (or cutting/mowing them at different frequencies). There was one study in each of USA, the Netherlands, Belgium and Italy.

VEGETATION COMMUNITY

Community composition (1 study): One replicated, randomized, paired, controlled study of farmland ditches in the Netherlands found that marshy areas cut once, twice or three times/year had a similar overall plant community composition, when surveyed in July.
Overall richness/diversity (2 studies): Two replicated, paired, controlled studies in farmland ditches in the Netherlands and wet grasslands in Belgium reported that overall plant species richness was similar in plots cut once or twice/year (and three times/year in the Netherlands).

VEGETATION ABUNDANCE

Overall abundance (1 study): One replicated, paired, controlled, before-and-after study in wet grasslands in Belgium reported that the effect of cutting twice/year (in July and October) on total above-ground biomass was intermediate between the effects of cutting once/year in July or October.
Individual species abundance (4 studies): All four studies quantified the effect of this action on the abundance of individual plant species. For example, one replicated, paired, controlled study in freshwater marshes in the USA reported that cattail Typha spp. biomass was greater, nine months after the last cut, in plots cut every six weeks than in plots cut every three weeks. One paired, controlled, before-and-after study in reedbeds in Italy found that common reed Phragmites australis biomass was similar in plots mown once or twice/year, when measured at least five months after the last cut.

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, paired, controlled study in 1980–1981 in two artificial water treatment marshes dominated by cattails Typha spp. in Michigan, USA (Ulrich & Burton 1984) reported that cutting cattail less frequently during one summer increased its biomass the following summer. Statistical significance was not assessed. Nine months after the last cut, cattail biomass was 390 g/m²in plots cut every six weeks and 190 g/m² in plots cut every three weeks. There was a similar but less extreme pattern one year after the last cut: cattail biomass was 760 g/m²in plots cut every six weeks and 600 g/m² in plots cut every three weeks. At both times, cattail biomass in uncut plots was 620 g/m². Methods: In June 1980, nine plots were established in each of two cattail-dominated marshes. Over 12 weeks, six plots (three plots/marsh) were cut every six weeks and six plots (three plots/marsh) were cut every three weeks. Cuttings were removed. The remaining six plots remained undisturbed. In June and August 1981, above-ground cattail biomass was collected from each plot, then dried and weighed.
Study and other actions tested
Referenced paper
Ulrich K.E. & Burton T.M. (1984) The establishment and management of emergent vegetation in sewage-fed artificial marshes and the effects of these marshes on water quality. Wetlands, 4, 205-220.
A replicated, randomized, paired, controlled study in 1989–1991 of four farmland ditches in the Netherlands (Best 1994) found that vegetation cutting had similar effects on the plant community in the emergent wetland zone, whether it was done once, twice or three times/year. The overall plant community composition was statistically similar under each cutting frequency in three of three years (data reported as statistical model results). Plant species richness was similar under each cutting frequency in 10 of 12 comparisons (for which one cut: 10–49; two cuts: 8–48; three cuts: 9–49 species/ditch). The study also identified 16 common emergent and terrestrial plant species whose cover was significantly affected by the frequency of cutting in at least one ditch (data not reported). Methods: Between 1989 and 1991, vegetation was cleared from three 20 m sections of each ditch: one section each May; one section each May and July; one section each May, July and September. Vegetation was cut within the ditch and on its margins, then dumped higher up on the ditch banks. Each July, plant species and their cover (excluding mosses) were recorded in the emergent wetland zone (influenced by water, parts seasonally flooded) bordering each ditch.
Study and other actions tested
Referenced paper
Best E.P.H. (1994) The impact of mechanical harvesting regimes on the aquatic and shore vegetation in water courses of agricultural areas of the Netherlands. Vegetatio (now Plant Ecology), 112, 57-71.
A replicated, paired, controlled, before-and-after study in 1986–1988 in five wet grasslands in Belgium (Dumortier et al. 1996) reported that mowing plots once per year increased plant species richness and sometimes increased plant biomass, whilst mowing twice per year increased plant species richness and reduced plant biomass. Statistical significance was not assessed. Over two years, plant species richness increased whether plots were mown once per year (July: from 15 to 18 species/6 m²; October: from 19 to 20 species/6 m²) or twice per year (July and October: from 17 to 19 species/6 m²). Total above-ground biomass (including litter) increased in plots mown in July (from 460 to 490 g/m²), but declined in plots mown in October (from 730 to 480 g/m²) or July and October (from 660 to 630 g/m²). The study also included some data on the abundance of individual plant species under each mowing regime (see original paper). Methods: In spring 1986, three 7 x 7 m plots were established in each of five adjacent wet grasslands (mown annually for the previous 10 years). From 1986, five plots (one plot/grassland) were mown in July, five were mown in October, and five were mown in July and October. Cuttings were removed. Plant species were recorded each summer between 1986 and 1988. Biomass was cut and collected from five 30 x 30 cm quadrats/plot/year, immediately before the first mow (so not at the same time in all plots), then dried and weighed.
Study and other actions tested
Referenced paper
Dumortier M., Verlinden A., Beeckman H. & Van D.M.K. (1996) Effects of harvesting dates and frequencies on above and below-ground dynamics in Belgian wet grasslands. Écoscience, 3, 190-198.
A paired, controlled, before-and-after study in 2000–2002 in two lakeshore reedbeds in northern Italy (Fogli et al. 2014) found that plots mown once or twice each year supported similar common reed Phragmites australis biomass after two years. In both reedbeds, above-ground reed biomass was statistically similar in plots mown once each year (in winter; 625–1,751 g/m²) and plots mown twice each year (in summer and winter; 370–1,153 g/m²). Before mowing, reed biomass was statistically similar in plots destined for each treatment (477–668 g/m²). Methods: In July 2000, a pair of 10 x 10 m plots was established in each of two reedbeds on the shore of Lago di Aslerio. 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). Cuttings were removed. The reedbeds had been historically mown in winter (and sometimes in summer), but not for >30 years. 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
Referenced paper
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.

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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