Vegetation change in a man‐made salt marsh affected by a reduction in both grazing and drainage

Published source details Esselink P., Fresco L.F.M. & Dijkema K.S. (2002) Vegetation change in a man‐made salt marsh affected by a reduction in both grazing and drainage. Applied Vegetation Science, 5, 17-32.
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This study is summarised as evidence for the following.

	Action	Category
	Raise water level to restore degraded brackish/salt marshes Action Link
	Reduce intensity of livestock grazing: brackish/salt marshes Action Link
	Exclude or remove livestock from historically grazed brackish/salt marshes Action Link

Raise water level to restore degraded brackish/salt marshes

A study in 1981–1997 of a salt marsh in the Netherlands (Esselink et al. 2002) found that following abandonment of drainage systems from 1981 (along with legal protection and a reduction in grazing intensity), there were changes in the area of plant community types and the abundance of some dominant species, and an increase in plant species richness. Between 1981 and 1995, the area covered by pioneer succulents increased (from 0% to 19% of the marsh) and the area covered by short-grass communities decreased (from 76% to 56%). Statistical significance of these cover results was not assessed. Between 1983 and 1997, the frequency of two of the most abundant plant species did not significantly change: saltmarsh grass Puccinellia maritima (1983: present in 81% of plots; 1997: present in 84% of plots) and sea aster Aster tripolium (1983: 80%; 1997: 97%). Species showing significant changes in frequency included saltbush Atriplex prostrata (increase from 86% to 98%), seablite Suaeda maritima (increase from 38% to 70%), creeping bentgrass Agrostis stolonifera (decrease from 78% to 69%) and common cordgrass Spartina anglica (decrease from 52% to 31%). Between 1983 and 1997, plant species richness significantly increased: from 8 species/100 m² to 10 species/100 m². Methods: A degraded coastal salt marsh became part of a nature reserve in 1981. The drainage system was abandoned by 1984 (making the soils wetter and less aerated), and cattle grazing intensity was gradually reduced (reaching 40–80 animal days/ha/season by the 1990s). Note that this study evaluates the combined effect of these interventions. Coverage of vegetation types was calculated from maps of the marsh made in 1981 and 1995. Plant species presence and cover were surveyed in 64 permanent 100-m² plots, spread across four parts of the marsh and at a range of elevations, in 1983, 1991 and 1997.

(Summarised by: Nigel Taylor)
Reduce intensity of livestock grazing: brackish/salt marshes

A study in 1981–1997 of a salt marsh in the Netherlands (Esselink et al. 2002) reported that following a reduction in grazing intensity from 1981 (along with legal protection and abandonment of drainage systems), there were changes in the area of plant community types and the abundance of some dominant species, and an increase in plant species richness. Between 1981 and 1995, the area covered by pioneer succulents increased (from 0% to 19% of the marsh) and the area covered by short-grass communities decreased (from 76% to 56%). Statistical significance of these cover results was not assessed. Between 1983 and 1997, the frequency of two of the most abundant plant species did not significantly change: saltmarsh grass Puccinellia maritima (1983: present in 81% of plots; 1997: present in 84% of plots) and sea aster Aster tripolium (1983: 80%; 1997: 97%). Species showing significant changes in frequency included saltbush Atriplex prostrata (increase from 86% to 98%), seablite Suaeda maritima (increase from 38% to 70%), creeping bentgrass Agrostis stolonifera (decrease from 78% to 69%) and common cordgrass Spartina anglica (decrease from 52% to 31%). Between 1983 and 1997, plant species richness significantly increased: from 8 species/100 m² to 10 species/100 m². Methods: A degraded coastal salt marsh became part of a nature reserve in 1981. Cattle grazing intensity was gradually reduced (reaching 40–80 animal days/ha/season by the 1990s), and the drainage system was abandoned by 1984 (making the soils wetter and less aerated). Note that this study evaluates the combined effect of these interventions. Coverage of vegetation types was calculated from maps of the marsh made in 1981 and 1995. Plant species presence and cover were surveyed in 64 permanent 100-m² plots, spread across four parts of the marsh and at a range of elevations, in 1983, 1991 and 1997.

(Summarised by: Nigel Taylor)
Exclude or remove livestock from historically grazed brackish/salt marshes

A replicated, paired, controlled study in 1991–1998 in a salt marsh in the Netherlands (Esselink et al. 2002) reported that plots fenced to exclude cattle contained fewer plant species than grazed areas, and developed cover of different plant species. Statistical significance was not assessed. After seven years, plots from which cattle had been excluded had lower plant species richness (8–9 species/100 m²) than areas that remained grazed (13–14 species/100 m²). Exclusion plots were dominated or co-dominated by a mix of species, including couch grass Elymus repens (7–90% cover/plot), creeping bent Agrostis stolonifera (1–40% cover/plot) and saltmarsh grass Puccinellia maritima (0–50% cover/plot). In contrast, grazed plots were all dominated by saltmarsh grass (50–80% cover/plot). Couch grass and creeping bent showed particularly strong responses to the seven years of exclusion: cover of these species was 0–1% in the spring immediately following exclusion, and never more than 2% in grazed plots. Methods: In 1991, two 40 x 40 m plots within a grazed salt marsh were fenced and cattle were successfully excluded. One plot was closer to the sea and one closer to the land. Between 1991 and 1998, vegetation was surveyed in 10 x 10 m quadrats: two within each plot and three in the grazed marsh (38–81 animal days/ha/year) around each plot.

(Summarised by: Nigel Taylor)