Reduce intensity of livestock grazing: freshwater marshes

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

Study locations

Key messages

  • Three studies evaluated the effects, on vegetation, of reducing livestock grazing intensity in freshwater marshes (without stopping grazing entirely). Two studies were in the USA and the other was in Ireland. In all three studies, livestock were cattle.

VEGETATION COMMUNITY

  • Community composition (1 study): One site comparison study in Ireland found that lightly and heavily grazed wet meadows contained a similar overall mix of plant species.
  • Relative abundance (1 study): One replicated, randomized, paired, controlled study in the USA found that seasonally and continuously grazed ephemeral pools had similar cover of grasses relative to forbs.
  • Overall richness/diversity (1 study): One site comparison study in Ireland found that lightly and heavily grazed wet meadows had similar overall plant species richness.
  • Native plant richness/diversity (1 study): One replicated, randomized, paired, controlled study in the USA found that seasonally and continuously grazed ephemeral pools experienced similar changes in native plant species richness over three years.

VEGETATION ABUNDANCE

  • Overall abundance (1 study): One site comparison study in Ireland reported that lightly and heavily grazed wet meadows had similar overall vegetation cover.
  • Herb abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in the USA found that lightly and moderately grazed springs/creeks had similar herb cover.
  • Individual species abundance (1 study): One study quantified the effect of this action on the abundance of individual plant species. The site comparison study in Ireland reported, for example, that lightly grazed wet meadows had greater cover of black sedge Carex nigra, and lower cover of creeping bent Agrostis stolonifera, than more heavily grazed wet meadows.

VEGETATION STRUCTURE

  • Height (1 study): One site comparison study in Ireland found that lightly grazed wet meadows contained taller vegetation than heavily grazed wet meadows. Vegetation was measured in the summer, during the grazing season.

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, randomized, paired, controlled, before-and-after study in 1992–1997 of springs and creeks in California, USA (Allen-Diaz & Jackson 2000) found that lightly and moderately grazed areas had statistically similar herbaceous vegetation cover. This was true in five of five years, both in spring wetlands (data not reported) and in downstream wetlands alongside creeks (lightly grazed: 46–47%; heavily grazed: 35–80%). Before intervention, the creek plots had 58–80% herb cover. Methods: Three pairs of pastures were selected for the study. All contained springs and had been moderately grazed by cattle since 1960 (800–1,000 kg/ha Residual Dry Matter: the amount of herbaceous material present left after grazing). From 1992/1993, one random pasture/pair remained moderately grazed (1,100–1,800 kg/ha RDM) and one was lightly grazed (1,200–3,800 kg/ha RDM). Grazing occurred in November and February–May. Vegetation cover was monitored in late May 1992–1997, along four 5–10 m transects/pasture: two in wetlands near the spring source, and two in wetlands along the resulting creek.

    Study and other actions tested
  2. A replicated, randomized, paired, controlled study in 2000–2003 of ephemeral pools in a grassland in California, USA (Marty 2005) found that seasonally grazed pools typically had similar relative cover of grasses and native plants to continuously grazed pools, and experienced similar changes in native plant richness. In six of six comparisons over three years, seasonally and continuously grazed pools had similar cover of grasses relative to forbs (seasonal: grass cover 46–55% of forb cover; continuous: 34–48%). In three of six comparisons, seasonally and continuously grazed pools had similar relative cover of native plants relative to non-natives. In the other three comparisons, seasonally grazed pools had lower relative cover of native plants than continuously grazed pools (data not reported). Finally, over the three years, seasonally and continuously grazed pools experienced statistically similar changes in native plant species richness (seasonal: 0.6 fewer to 1.2 more species/0.25 m2; continuous: 0.7–1.8 more species/0.25 m2). Methods: In 2000, eighteen plots were established (in six sets of three) on a ranch grazed for >100 years. In each set, one plot was grazed in the dry season, one was grazed in the wet season, and one was grazed throughout both seasons. Plots were grazed by 1 cow-calf pair/2.4 ha. Access to the seasonally grazed plots was controlled by electric fences. Each spring between 2001 and 2003, vegetation was surveyed in three pools/plot and in adjacent upland. Pools were 70–1,130 m2 and dry when surveyed.

    Study and other actions tested
  3. A site comparison study in 2001 of three wet meadows around an ephemeral lake in Ireland (Ryder et al. 2005) found that lightly and heavily grazed meadows had a similar plant community composition, species richness and overall cover, but that lightly grazed meadows contained taller vegetation. Both lightly and heavily grazed wet meadows had a statistically similar mix of plant species (data reported as a similarity index) and statistically similar plant species richness (lightly grazed: 18 species/150m2 and 15 species/m2; heavily grazed: 17–21 species/150m2 and 15–16 species/m2). Overall vegetation cover was 99% in both lightly grazed and heavily grazed meadows. However, the lightly grazed meadow had greater cover of black sedge Carex nigra cover and lower cover of creeping bent Agrostis stolonifera (data reported as abundance classes; see original paper for data on other species). Statistical significance of cover results was not assessed. The lightly grazed meadow had significantly taller vegetation on average (35 cm) than the heavily-grazed meadows (17 cm). Methods: In 2001, wet meadow vegetation was surveyed in three fields with different cattle grazing intensities. One field was lightly grazed (0.01 cows/ha/day, averaged across the summer) and two were heavily-grazed (0.67–0.76 cows/ha/day, averaged across the summer). In July, vegetation height was recorded at 72 points/field. In September, plant species and the area of bare ground/rock were recorded in six 1m2 quadrats/field.

    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

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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