Use barriers to keep livestock off ungrazed brackish/salt marshes

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

60%
Certainty

35%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

This action involves excluding livestock – with physical barriers such as fences or hedgerows, or virtual barriers involving GPS trackers and negative sounds or electric shocks (SRUC 2015) – from an area of natural, ungrazed marsh or swamp. Here, “ungrazed” refers to the recent history of a site, so studies of sites that have not been recently grazed and so have regained their natural ecological character would also be included here.

Domestic livestock can directly consume vegetation, destroy vegetation by trampling, create bare patches of ground (e.g. repeatedly used tracks), affect water infiltration and flows by compacting soils, affect nutrient balance through excretion of waste products, and import seeds of undesirable plants (Morris & Reich 2013).

^{Morris K. & Reich P. (2013) Understanding the Relationship Between Livestock Grazing and Wetland Condition. Arthur Rylah Institute for Environmental Research, Technical Report Series No. 252.}

^{SRUC (2015) Virtual Fencing Systems for Livestock. Available at https://www.sruc.ac.uk/download/downloads/id/3128/virtual_fencing_systems_for_livestock.pdf. Accessed 7 January 2020.}

Study locations

Key messages

One study evaluated the effects, on vegetation, of using barriers to keep livestock off brackish/salt marshes that have never (or not recently) been grazed. The study was in the UK.

VEGETATION COMMUNITY

Overall richness/diversity (1 study): One replicated, controlled study in a salt marsh in the UK reported that plots fenced to exclude sheep contained more plant species, after four years, than plots that became grazed by sheep.

VEGETATION ABUNDANCE

Overall abundance (1 study): One replicated, controlled study in a salt marsh in the UK reported that plots fenced to exclude sheep contained more vegetation biomass, after two years, than plots that became grazed by sheep.
Individual species abundance (1 study): The same study also quantified the effect of this action on the abundance of individual plant species. For example, plots fenced to exclude sheep contained more cordgrass Spartina and less saltbush Atriplex hastata, after four years, than plots that became grazed by sheep.

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, controlled study in 1955–1959 in an estuarine salt marsh in England, UK (Ranwell 1961) reported that plots from which livestock were excluded contained more overall vegetation biomass and more plant species than plots that became grazed, and that exclusion had mixed effects on the abundance of individual plant species. Statistical significance was not assessed. After two years, exclusion plots contained 7,293 g/m² above-ground vegetation biomass (vs grazed: 5,325 g/m²; start of experiment: 7,720 g/m²). After four years, exclusion plots contained 9 plant species in total (vs grazed: 6; start of experiment: 5). Exclusion plots contained less cordgrass Spartina sp. and saltmarsh grass Puccinellia maritima than grazed plots, and more saltbush Atriplex hastata. For example, cover of mature cordgrass plants was only 5–59% in exclusion plots after four years (vs grazed: 64–89%) and cordgrass biomass declined more strongly over the first two years in exclusion plots (by 288 g/m²) than grazed plots (by 167 g/m²). See original paper for full data. Methods: In summer 1955, eight 9 x 13 m plots were established in a cordgrass-dominated salt marsh. Four plots were fenced to exclude sheep. Sheep were introduced to graze the other four plots (summer only; average 32 sheep days/plot/year). Vegetation was surveyed in early June at the start of the experiment (1955) and over the four following years (1956–1959). Biomass was dried before weighing.
Study and other actions tested
Referenced paper
Ranwell D.S. (1961) Spartina salt marshes in southern England: I. The effects of sheep grazing at the upper limits of Spartina marsh in Bridgwater Bay. Journal of Ecology, 49, 325-340.

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

Related Actions

Actions	Effectiveness	Studies	Category
Change season/timing of livestock grazing: brackish/salt marshes Action Link	Likely to be beneficial	2	Synopsis Link
Exclude or remove livestock from historically grazed freshwater marshes Action Link	Likely to be beneficial	10	Synopsis Link
Change season/timing of livestock grazing: freshwater swamps Action Link	No evidence found (no assessment)	0	Synopsis Link