Exclude or remove livestock from historically grazed freshwater marshes

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

Study locations

Key messages

  • Ten studies evaluated the effects, on vegetation, of excluding or removing livestock from historically grazed freshwater marshes. Seven studies were in the USA, two were in Morocco and one was in Australia. In all 10 studies the focal livestock included cattle (mixed with sheep in the two studies in Morocco). Two studies in the USA were based on the same experimental set-up, and the two studies in Morocco shared some study sites.

VEGETATION COMMUNITY

  • Community composition (4 studies): Two site comparison studies in Morocco and the USA reported that marshes/pools fenced to exclude livestock for 3–30 years contained a different overall plant community to grazed sites. In the USA, the precise effect depended on the time since exclusion. Two replicated, randomized, paired, controlled studies in marshes in Australia and the USA found that fencing to exclude cattle typically had no significant effect on the overall plant community composition after 1–14 years. One of the studies also found that the plant community in fenced and grazed marshes was of similar quality, relative to pristine local marshes.
  • Relative abundance (3 studies): Of three replicated, randomized, paired, controlled studies that reported data on the relative abundance of plant groups, two studies (based on one experimental set-up) in the USA found that ephemeral pools fenced to exclude cattle for 1–10 years had similar or greater cover of grasses relative to forbs than pools that remained grazed. The other study, also in the USA, found that the relative abundance of forbs, grass-like plants and shrubs was similar in marshes fenced to exclude cattle for 1–3 years and marshes that remained grazed.
  • Overall richness/diversity (6 studies): Four replicated studies (two also randomized, paired, controlled) in the USA, Morocco and Australia found that marshes/pools fenced to exclude cattle, for 1–30 years, typically had similar overall plant species richness to sites that remained grazed. One of the studies found that the same was true for overall plant diversity. One replicated, site comparison study of ephemeral pools in Morocco found that pools fenced to exclude livestock for >30 years had similar (in a dry year) or greater (in a wet year) plant species richness compared to pools that remained grazed. One site comparison study in the USA found that marshes fenced to exclude cattle for 3–13 years contained fewer plant species than grazed marshes, and had similar or lower plant diversity.
  • Characteristic plant richness/diversity (1 study): One site comparison study of ephemeral pools in Morocco found that pools fenced to exclude livestock for >30 years contained a similar number of wetland-characteristic plant species to pools that remained grazed.
  • Native/non-target richness/diversity (3 studies): Of three replicated, randomized, paired, controlled studies that reported data on native plant species richness, two studies (based on one experimental set-up) in the USA found that fencing ephemeral pools to exclude cattle for 1–10 years typically reduced native plant species richness. The other study, also in the USA, found that native plant species richness was similar in marshes fenced to exclude cattle for 1–3 years and marshes that remained grazed.

VEGETATION ABUNDANCE

  • Overall abundance (3 studies): Two replicated, site comparison studies in the USA and Morocco found that ponds/pools fenced to exclude cattle for >10 years contained more vegetation than sites that remained grazed. This was measured in terms of emergent cover around pond margins or peak above-ground biomass in ephemeral pools. One replicated, randomized, paired, controlled study in Australia found that marshes fenced to exclude cattle for ≤4 years contained similar above-ground vegetation biomass to marshes that remained grazed.
  • Characteristic plant abundance (1 study): One site comparison study of ephemeral pools in Morocco found that the overall abundance of wetland-characteristic plant species was greater in pools fenced to exclude livestock for >30 years than in pools that remained grazed.
  • Herb abundance (1 study): One replicated, randomized, paired, controlled, before-and-after study in the USA found that fencing pastures to exclude cattle typically increased herb cover in wetlands along creeks, but had no significant effect on herb cover within spring wetlands.
  • Individual species abundance (2 studies): Two replicated, randomized, paired, controlled studies in freshwater marshes in Australia and the USA quantified the effect of this action on the abundance of individual plant species (see original papers for data).

VEGETATION STRUCTURE

  • Visual obstruction (1 study): One replicated, site comparison study in the USA found that ponds fenced to exclude cattle for >10 years had greater horizontal vegetation cover, around their margins, than ponds that remained grazed.
  • Height (2 studies): Two replicated studies (one also randomized, paired, controlled, before-and-after) in the USA found that fencing ponds to exclude cattle, for 1–3 or >10 years, increased the height of vegetation around their margins.

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 excluding cattle typically increased herbaceous vegetation cover in creek wetlands, but had no significant effect in spring wetlands. In three of five years, ungrazed creek wetlands had higher herb cover (84–87%) than creek wetlands that remained grazed (46–59%). In the other two years, there was no significant difference between treatments (ungrazed: 46–59%; grazed: 46–59%). Before cattle exclusion, plots destined for each treatment had statistically similar herb cover (ungrazed: 59%; grazed: 46–59%). In all five years, ungrazed spring wetlands had statistically similar herb cover to grazed spring wetlands (data not reported). Methods: Nine pastures (three sets of three) 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, cattle were excluded from three pastures (one random pasture/set). The other pastures remained moderately or lightly grazed (1,100–3,800 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 within a grassland in California, USA (Marty 2005) found that excluding cattle increased the dominance of grasses, but reduced the dominance and richness of native plants. In the final two of three years, pools fenced to exclude cattle had greater relative grass cover (83–104% of forb cover) than pools that remained grazed (34–48% of forb cover). In three of three years, exclusion pools had lower relative cover of native vs non-native plants than grazed pools (data not reported). Over the three years, native species richness was stable or declined in exclusion pools (1.3 fewer to 0.1 more species/0.25 m2) whilst it increased in grazed pools (0.7–1.8 more species/0.25 m2). Methods: In 2000, six pairs of plots were established on a ranch grazed for >100 years. In each pair, one plot was fenced to exclude cattle whilst the other remained grazed (October–June; 1 cow-calf pair/2.4 ha). Each spring between 2001 and 2003, vegetation was surveyed in three dried-up pools (and adjacent upland) in each plot. Pools were 70–1,130 m2. Ungrazed pools were dry for longer than grazed pools. This study was based on the same experimental set-up as (9), but monitored it for less time.

    Study and other actions tested
  3. A replicated, randomized, paired, controlled, before-and-after study in 2002–2006 at the edges of 12 ponds in Oregon, USA (Adams et al. 2009) found that excluding cattle increased vegetation height. Comparing data over three years before and after intervention, the average height of emergent vegetation increased more around ponds that had been fenced to exclude cattle (before: 5–13 cm; after: 28–31 cm) than around ponds that remained grazed (before: 6 cm; after: 9–10 cm). Methods: Four clusters of three historically grazed ponds (112–4,200 m2) were selected for study. Between 2003 and 2005, four ponds (one random pond/cluster) received each fencing treatment: fully fenced (wooden or barbed wire fences, 1.5 m tall, 1–5 m from pond edge), half fenced (including a fence running across the pond) or not fenced (open to grazing June–September, 25–32 ha/cow-calf pair). The height of emergent vegetation was surveyed in late summer 2002–2006, for up to three years before and after fencing. Eight 2 x 2 m plots were sampled around the shoreline of each pond.

    Study and other actions tested
  4. A replicated, site comparison study in 2005–2006 at the edges of eight ponds in Tennessee, USA (Burton et al. 2009) found that ponds fenced to exclude cattle typically had taller vegetation with greater cover than ponds that remained grazed, but similar plant species richness. Exclusion ponds had significantly greater vegetation cover than grazed ponds in two of two years (exclusion: 42–45%; grazed: 25–30%), significantly taller vegetation, on average, in one of two years (for which exclusion: 73 cm; grazed: 42 cm), and significantly greater horizontal vegetation cover in one of two years (for which exclusion: 59%; grazed: 47%). In the other comparisons, there was no significant difference between exclusion and grazed ponds, but a strong trend towards greater cover. Total plant species richness never significantly differed between treatments (exclusion: 4.0–5.3 species/m2; grazed: 4.2–4.3 species/m2). Methods: In spring and summer 2005 and 2006, emergent vegetation was surveyed on the shoreline of eight small (<1.1 ha) farm ponds (one 1-m2 quadrat/pond/survey). Four ponds had been fenced to exclude cattle for >10 years. The other four ponds had been exposed to grazing (132 cattle/ha of wetland) continuously for >10 years.

    Study and other actions tested
  5. A replicated, site comparison study in 2009 of 16 ephemeral pools in Morocco (Bouahim et al. 2010) found that pools within areas fenced to exclude livestock for >30 years contained a different overall plant community to pools within grazed areas, with greater abundance of wetland-characteristic species – but that there was no significant difference in plant species richness. The overall plant community composition differed between exclusion and grazed pools (data reported as a graphical analysis; statistical significance of difference not assessed). Exclusion pools supported a higher total abundance of wetland-characteristic plant species than grazed pools (data not reported). However, exclusion and grazed pools contained a statistically similar number of wetland-characteristic plant species – and plant species overall (data not reported). Methods: In February and May 2009, vegetation was surveyed in 16 ephemeral pools (600–13,000 m2; water depth ≤85 cm) within a cork oak forest. Eight pools were in hunting reserves, from which livestock had been excluded since 1975. The other eight pools were open to cattle and sheep grazing. Cover/abundance of all plant species was recorded in two quadrats/pool/sample: one at the centre and one at the edge. Some of the pools from this study were also used in (6).

    Study and other actions tested
  6. A replicated, site comparison study in 2008–2009 of six ephemeral pools in Morocco (Bouahim et al. 2010) found that pools within areas fenced to exclude livestock for >30 years contained more vegetation biomass than pools within grazed areas, and more plant species in one of two years. Peak biomass was measured in 2008 only. Exclusion pools contained more above-ground biomass (123 g/m2) than grazed pools (42 g/m2). Plant species richness was measured in both 2008 and 2009. Exclusion pools contained a statistically similar number of plant species to ungrazed pools in 2008 (a dry year), but more plant species than ungrazed pools in 2009 (a wet year) (data not reported). Methods: Vegetation was surveyed in six ephemeral pools within a cork oak forest. Three pools were in hunting reserves, from which livestock had been excluded since 1975. The other three pools were open to cattle and sheep grazing. In February 2008, vegetation was cut from nine 1-m2 quadrats/pool, then dried and weighed. Between January and June 2008 and 2009, plant species were recorded in fifteen 900-cm2 quadrats/pool. All quadrats were evenly spread across different elevations. This study used a subset of the pools from (5).

    Study and other actions tested
  7. A replicated, randomized, paired, controlled study in 1994–2008 in three marshes on a floodplain in New South Wales, Australia (Berney et al. 2014) found that plots fenced to exclude cattle typically contained a similar plant community, with similar species richness and biomass, to plots that remained grazed by cattle. In the first four years after intervention, exclusion and grazed plots had a similar overall plant community composition (26 of 26 comparisons; data reported as graphical analyses), similar overall plant species richness (26 of 26 comparisons; 3–19 vs 3–17 species/m2) and similar plant biomass (3 of 3 comparisons; 630–1,300 vs 430–1,130 g/m2). After 13–14 years, exclusion and grazed plots had a similar plant community composition in seven of nine comparisons (data reported as a graphical analysis) and similar plant species richness in five of nine comparisons (exclusion: 5–19; grazed: 10–17 species/m2). Plant species richness was higher in exclusion than grazed plots in two comparisons (both in one marsh) and lower in exclusion than grazed plots in two comparisons (both in one marsh). The study also reported data on the cover of individual plant species (see original paper). Methods: In early 1994, twelve pairs of 25 x 25 m plots were established in three historically grazed marshes (four pairs/marsh). In each pair, one random plot was fenced to exclude domestic cattle (but not wild herbivores). The other plot was not fenced and was open to all herbivores, including 0.5–2.0 cows/ha. In 1994–1998 (a wetter period) and 2007–2008 (a drier period), plant species and their cover were recorded in ten 1-m2 quadrats/plot. In May 1998, live above-ground biomass was collected from two 0.25-m2 quadrats/plot, then dried and weighed.

    Study and other actions tested
  8. A site comparison study in 2009 of three ephemeral freshwater marshes in Oregon, USA (Kidd & Yeakley 2015) reported that the effects of cattle exclusion on the plant community depended on the duration of exclusion. Both marshes from which cattle had been excluded had a significantly different plant community composition to a marsh that remained grazed (data reported as a graphical analysis). However, this involved lower relative cover of native species in the long-term exclosure (4% of total) than in the grazed marsh (23% of total), but greater relative cover of native species in the short-term exclosure (52% of total). Both exclosures had lower plant species richness (total: 6–12; native: 3–6; non-native: 3–5 species/transect) than the grazed marsh (total: 23; native: 10; non-native: 12 species/transect). The long-term exclosure had lower plant diversity (total, native and non-native) than the grazed marsh (data reported as a diversity index). In contrast, the short-term exclosure had higher native plant diversity than the grazed marsh, and similar total and non-native diversity. Methods: In late summer 2009, vegetation was surveyed in three marshes (each <10 ha) within one river basin. Two marshes had been fenced to exclude cattle (one for three years, one for 13 years). The other marsh remained grazed (approximately 1.6 cattle/ha, April–September each year). Plant species and their cover were recorded along six 45–60 m transects/marsh.

    Study and other actions tested
  9. A replicated, randomized, paired, controlled study in 2000–2010 of ephemeral pools within a grassland in California, USA (Marty 2015) found that excluding cattle typically increased the dominance of grasses, but reduced the dominance and richness of native plants. In 5 of 10 years, pools fenced to exclude cattle had greater relative grass cover (1.2–4.8 times forb cover) than pools that remained grazed (0.2–1.7 times forb cover). In the other five years, there was no significant difference between exclusion and grazed pools. In 10 of 10 years, exclusion pools had lower relative cover of native plant species (0.3–0.6 times non-native cover) than grazed pools (0.5–0.7 times non-native cover). In 9 of 10 years, exclusion pools had lower native plant richness (5.8–6.8 species/0.25 m2) than grazed pools (8.0–9.0 species/0.25 m2). Methods: In 2000, six pairs of plots were established on a ranch grazed for >100 years. In each pair, one plot was fenced to exclude cattle whilst the other remained grazed (October–June; 1 cow-calf pair/2.4 ha). Each spring between 2001 and 2003, vegetation was surveyed in three dried-up pools (and adjacent upland) in each plot. Pools were 70–1,130 m2. Ungrazed pools were dry for longer than grazed pools. This study was based on the same experimental set-up as (2).

    Study and other actions tested
  10. A replicated, paired, controlled study in 2006–2009 in 40 freshwater marshes within a ranch in Florida, USA (Boughton et al. 2016) found that fencing to exclude cattle typically had no significant effect on the plant community composition, vegetation quality, species richness or diversity. Statistical significance was assessed for all results, but data were generally not reported. After 1–3 summers, the overall plant community composition was similar in marshes fenced to exclude cattle and marshes that remained grazed (data not reported). The same was true for the relative abundance of forbs, grass-like plants and shrubs. However, the relative abundance of dogfennel Eupatorium capillifolium was greater in exclusion marshes (2–5%) than in grazed marshes (0–1%). Exclusion and open marshes also had similar overall plant species diversity and richness, and similar native plant species richness. In two of three years, the extent to which species were characteristic of pristine Florida marshes was similar in exclusion and open marshes (data reported as a conservatism score). In the other year, the effect of cattle exclusion on this outcome was more complicated, differing between marshes and depending on whether they were burned or not. The study also reported data on the frequency of individual plant species (see original paper). Methods: The study used forty 0.5–1.5 ha marshes, grouped into five blocks of eight, within a 4,000-ha ranch. In February 2007, twenty marshes (four marshes/block) were fenced with barbed wire to exclude cattle (but not other mammals). The other 20 marshes (four marshes/block) were left open to cattle. In each block, two fenced and two grazed marshes were also burned in February 2008. Plant species presence/absence was recorded in October before (2006) and after (2007–2009) fencing, in fifteen 1-m2 quadrats/marsh.

    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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