Study

Spartina salt marshes in southern England: I. The effects of sheep grazing at the upper limits of Spartina marsh in Bridgwater Bay

  • Published source details 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

Actions

This study is summarised as evidence for the following.

Action Category

Use grazing to maintain or restore disturbance: brackish/salt marshes

Action Link
Marsh and Swamp Conservation

Use barriers to keep livestock off ungrazed brackish/salt marshes

Action Link
Marsh and Swamp Conservation

Exclude or remove livestock from historically grazed brackish/salt marshes

Action Link
Marsh and Swamp Conservation
  1. Use grazing to maintain or restore disturbance: brackish/salt marshes

    A replicated, controlled study in 1955–1957 in an estuarine salt marsh in England, UK (Ranwell 1961) reported that continued grazing reduced total vegetation biomass, but had mixed effects on the abundance of dominant plant species. Unless specified, statistical significance was not assessed. At the start of the experiment, total above-ground vegetation biomass was 8,061 g/m2. After two years, this was only 5,633 g/m2 in grazed plots, vs 7,118 g/m2 in ungrazed plots. Over two years, saltmarsh grass Puccinellia maritima biomass increased more in grazed plots (by 99%) than in ungrazed plots (by 80%). Saltmarsh grass cover significantly increased in four of four grazed plots, but did not significantly change in three of four ungrazed plots (data not reported). Cordgrass Spartina sp. biomass declined less in grazed plots (by 67%) than in ungrazed plots (by 97%). Saltbush Atriplex hastata biomass declined more in grazed plots (by 277%) than in ungrazed plots (by 70%). Cover of these species typically declined significantly in both grazed and ungrazed plots. Methods: In summer 1955, eight 9 x 13 m plots were established in a historically grazed salt marsh. Four plots continued to be grazed by sheep during summer (average 24 sheep days/plot/year). Four plots were fenced to exclude sheep. Vegetation was surveyed in early June at the start of the experiment (1955) and over the two following years (1956–1957). Biomass was dried before weighing.

    (Summarised by: Nigel Taylor)

  2. Use barriers to keep livestock off ungrazed brackish/salt marshes

    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.

    (Summarised by: Nigel Taylor)

  3. Exclude or remove livestock from historically grazed brackish/salt marshes

    A replicated, controlled study in 1955–1957 in an estuarine salt marsh in England, UK (Ranwell 1961) reported that excluding livestock maintained greater overall vegetation biomass than continued grazing, but had mixed effects on the abundance of dominant plant species. Unless specified, statistical significance was not assessed. At the start of the experiment, total above-ground vegetation biomass was 8,061 g/m2. After two years, this had declined to 7,118 g/m2 in exclusion plots, vs 5,633 g/m2 in grazed plots. Over two years, saltbush Atriplex hastata biomass declined less in exclusion plots (by 70%) than in grazed plots (by 277%). In contrast, cordgrass Spartina sp. biomass declined more in exclusion plots (by 97%) than in grazed plots (by 67%) and saltmarsh grass Puccinellia maritima biomass increased less in exclusion plots (by 80%) than in grazed plots (by 99%). Changes in cover were typically similar in both exclusion and grazed plots. Exceptionally, saltmarsh grass cover did not significantly change in three of four exclusion plots but significantly increased in four of four grazed plots (data not reported). Methods: In summer 1955, eight 9 x 13 m plots were established in a historically grazed salt marsh. Four plots were fenced to exclude sheep. Four plots were grazed by sheep during summer (average 24 sheep days/plot/year). Vegetation was surveyed in early June at the start of the experiment (1955) and over the two following years (1956–1957). Biomass was dried before weighing.

    (Summarised by: Nigel Taylor)

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