Use barriers to keep livestock off ungrazed brackish/salt marshes
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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).
Related actions: Exclude or remove livestock from historically grazed brackish/salt marshes; Use grazing to maintain or restore disturbance; Use grazing to control problematic plants; Exclude wild vertebrates; Use fences or barriers to protect planted areas.
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.
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