Grazed vegetation mosaics do not maximize arthropod diversity: evidence from salt marshes

Published source details van Klink R., Rickert C., Vermeulen R., Vorst O., WallisDeVries M.F. & Bakker J.P. (2013) Grazed vegetation mosaics do not maximize arthropod diversity: evidence from salt marshes. Biological Conservation, 164, 150-157.
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This study is summarised as evidence for the following.

	Action	Category
	Reduce intensity of livestock grazing: brackish/salt marshes Action Link
	Employ areas of semi-natural habitat for rough grazing (includes salt marsh, lowland heath, bog, fen) Action Link
	Exclude or remove livestock from historically grazed brackish/salt marshes Action Link

Reduce intensity of livestock grazing: brackish/salt marshes

A replicated, paired, controlled study in 1988–2010 on three salt marshes in northern Germany (van Klink et al. 2013) found that moderately grazed plots contained a mosaic of short (species-rich) and tall (species-poor) vegetation patches, whilst heavily grazed plots contained only short vegetation. After 19–22 years, heavily grazed paddocks contained uniformly short and species-rich vegetation (5.0 cm canopy height; 7.3 plant species/0.33 m²; dominated by red fescue Festuca rubra: 35% cover). Moderately grazed paddocks contained some short, species-rich vegetation patches that were statistically similar to heavily grazed paddocks (5.8 cm canopy height; 5.8 plant species/0.33 m²; dominated by red fescue: 49% cover). They also contained taller vegetation patches with lower species richness than heavily grazed paddocks (19.4 cm canopy height; 5.3 plant species/0.33 m²; dominated by sea couch Elytrigia atherica: 46% cover). Paddock-scale species richness, which included both short and tall patches in the moderately grazed plots, did not significantly differ between treatments (moderate: 13.3; heavy: 14 plant species/1.1 m²). Methods: The study used six 11–15 ha paddocks: one pair on each of three coastal salt marshes (historically heavily grazed by sheep). From 1988 or 1991, one paddock/pair remained heavily grazed (10 sheep/ha, May–October) and the other was moderately grazed (3–4 sheep/ha, May–October). Vegetation was surveyed in summer 2010, in sixteen 30-cm-diameter circular quadrats/paddock. In moderately grazed paddocks, quadrats were split evenly across short and tall patches. All quadrats were at a similar elevation (±10 cm). This study included the paddocks used in (4).

(Summarised by: Nigel Taylor)
Employ areas of semi-natural habitat for rough grazing (includes salt marsh, lowland heath, bog, fen)

A replicated, paired, controlled study in 1988–2010 in three saltmarshes in Schleswig-Holstein, Germany (van Klink et al. 2013, same experimental set-up as 5 and 9) reported that lightly grazed saltmarsh had a higher abundance of two moth caterpillars, but a lower abundance of four caterpillars, than ungrazed saltmarsh, and heavily grazed marsh had a lower abundance of all species. Results were not tested for statistical significance, and data were not presented. In lightly grazed saltmarsh, two caterpillars (wormwood case-bearer Coleophora artemisiella and saltern-rush case-bearer Coleophora adjunctella) were more abundant than in heavily grazed or ungrazed marsh. Four species (maritime bell Eucosma lacteana, saltmarsh bell Eucosma tripoliana/pale saltern bell E. rubescana, common sea groundling Scrobipalpa nitentella, netted bagworm Whittleia retiella) were more abundant in ungrazed marsh than in grazed marshes, and one species (saltmarsh case-bearer Coleophora atriplicis) occurred in similar numbers in all marshes. None of the seven species recorded were more abundant in heavily grazed saltmarsh than in lightly grazed or ungrazed marsh. In 1988–1991, three heavily grazed (10 sheep/ha) saltmarshes were each divided into three paddocks (11–15 ha) and assigned to either heavy (10 sheep/ha), light (3–4 sheep/ha) or no (0 sheep/ha) grazing. The marshes were grazed from May–October, with sheep removed only during flooding events. In September 2010, moth caterpillars were sampled in sixteen 30-cm diameter points/paddock. In lightly grazed paddocks, eight points were in taller vegetation and eight in short vegetation. Caterpillars were collected by suction sampling (30 seconds), followed by removing and sieving all vegetation above 3 cm, and another 30-second suction sample.

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

A replicated, paired, controlled study in 1988–2010 on three salt marshes in northern Germany (van Klink et al. 2013) found that paddocks from which sheep had been removed contained taller vegetation than paddocks which remained grazed, but a similar number of plant species. After 19–22 years, the vegetation canopy was taller in ungrazed paddocks (25 cm) than in all grazed paddocks (5–19 cm). At a large scale, plant species richness did not significantly differ between ungrazed paddocks (10.3 species/1.1 m²) and all grazed paddocks (13.3–14.0 species/1.1 m²). However, at a smaller scale, ungrazed paddocks contained fewer plant species (4.1 species/0.33 m²) than heavily grazed paddocks (7.3 species/0.33 m²) or short vegetation patches in moderately grazed paddocks (5.8 species/0.33 m²) – but a similar number of plant species to tall vegetation patches in moderately grazed paddocks (5.3 species/0.33 m²). The study also reported cover of the dominant species in each paddock (see original paper for data). Methods: The study used nine 11–15 ha paddocks: three on each of three coastal salt marshes (historically heavily grazed by sheep). From 1988 or 1991, sheep were removed from one paddock/set. The other paddocks were grazed each summer, either moderately (3–4 sheep/ha) or heavily (10 sheep/ha). Vegetation was surveyed in summer 2010, in sixteen 30-cm-diameter circular quadrats/paddock. All quadrats were at a similar elevation (±10 cm). This study included the paddocks used in [11].

(Summarised by: Nigel Taylor)