The effects of livestock grazing on foliar arthropods associated with bird diet in upland grasslands of Scotland

Maintain upland heath/moorland

A replicated, randomized, controlled study in 2003–2005 on an upland grassland in Perthshire, UK (Dennis et al. 2008, same experimental set-up as 2) found that the abundance of moth caterpillars was higher in ungrazed plots compared to lightly or commercially grazed plots after 30 months. After 18 months of grazing, there was no significant difference in the number of caterpillars on ungrazed (2.8 individuals/plot), lightly grazed (1.9–2.4 individuals/plot) and commercially grazed plots (2.3 individuals/plot). However, after 30 months, there were more caterpillars in the ungrazed plots (4.9 individuals/plot) than in the lightly grazed (1.9–2.4 individuals/plot) or commercially grazed plots (0.5 individuals/plot). From January 2003, three grazing regimes (light grazing: sheep at 0.9 ewes/ha; mixed grazing: sheep and cattle equivalent to 0.9 ewes/ha; commercial grazing: sheep at 2.7 ewes/ha) and an ungrazed treatment were replicated six times each in twenty-four 3.3-ha plots (in three pairs of adjacent blocks). Caterpillars were sampled by sweep net in 2003–2005.

(Summarised by: Andrew Bladon, edited from Farmland Synopsis)

Use mixed stocking

A replicated, randomized, controlled study in 2003–2005 on an upland grassland in Perthshire, UK (Dennis et al. 2008, same experimental set-up as 3) found that mixed stocking did not affect the abundance of moth caterpillars under low intensity grazing. After 18 months of grazing, there was no significant difference in the number of caterpillars on lightly grazed mixed stocking (2.4 individuals/plot), sheep-only (1.9 individuals/plot), ungrazed (2.8 individuals/plot) and commercially grazed plots (2.3 individuals/plot). After 30 months, the number of caterpillars remained similar in the mixed stocking (2.4 individuals/plot) and sheep-only (1.9 individuals/plot) plots, but this was lower than in the ungrazed plots (4.9 individuals/plot) and higher than in the commercially grazed plots (0.5 individuals/plot). From January 2003, three grazing regimes (mixed: sheep and cattle equivalent to 0.9 ewes/ha; sheep-only: sheep at 0.9 ewes/ha; commercial: sheep at 2.7 ewes/ha) and an ungrazed treatment were replicated six times each in twenty-four 3.3-ha plots (in three pairs of adjacent blocks). Caterpillars were sampled by sweep net in 2003–2005.

(Summarised by: Andew Bladon, edited from Farmland Synopsis)

Reduce grazing intensity on grassland by reducing stocking density

A replicated, randomized, controlled study in 2003–2005 on an upland grassland in Perthshire, UK (Dennis et al. 2008, same experimental set-up as 3) found that plots grazed with a lower stocking density had a higher abundance of moth caterpillars than commercially grazed plots, but only after >2 years. After 18 months of grazing, there was no significant difference in the number of caterpillars on lightly grazed (1.9–2.4 individuals/plot), commercially grazed (2.3 individuals/plot) or ungrazed plots (2.8 individuals/plot). However, after 30 months, there were more caterpillars in the lightly grazed plots (1.9–2.4 individuals/plot) than in the commercially grazed plots (0.5 individuals/plot), but fewer than in the ungrazed plots (4.9 individuals/plot). From January 2003, three grazing regimes (light grazing: sheep at 0.9 ewes/ha or sheep and cattle equivalent to 0.9 ewes/ha; commercial grazing: sheep at 2.7 ewes/ha) and an ungrazed treatment were replicated six times each in twenty-four 3.3-ha plots (in three pairs of adjacent blocks). Caterpillars were sampled by sweep net in 2003–2005.

(Summarised by: Andew Bladon, edited from Farmland Synopsis)

Maintain upland heath/moorland

A randomized, replicated, controlled trial in 2002-2005 on an upland grassland site in Perthshire, Scotland, UK (Dennis et al. 2008) found that after 18 months of grazing, the biomass of arthropods associated with the bird diet was nearly twice as high on ungrazed/lightly grazed plots (sheep and cattle) than on plots grazed at a commercial stocking rate (sheep). The study also found more spiders (Araneae), true bugs (Hemiptera), beetles (Coleoptera) and caterpillars (Lepidoptera) in ungrazed or lightly grazed plots than in intensively grazed plots, but there was no straightforward relationship between grazing intensity and the number of cranefly (Tipulidae) adults and brachyceran flies (Brachycera). From January 2003, three grazing regimes (sheep at 2.7 ewes/ha, sheep at 0.9 ewes/ha, sheep and cattle equivalent to 0.9 ewes/ha) and an ungrazed control were replicated six times in 3.3 ha plots (in three pairs of adjacent blocks). Arthropods were sampled by suction sampler in spring/summer 2002-2005 (spiders, true bugs, beetles and brachyceran flies) and by sweep net in 2003-2005 (moth caterpillars and cranefly larvae, and cranefly adults in 2005).

Cease grazing on grassland to allow early succession

A replicated, randomized, controlled study in 2003–2005 on an upland grassland in Perthshire, UK (Dennis et al. 2008, same experimental set-up as 13) found that in ungrazed plots the abundance of moth caterpillars was higher than in grazed plots, but only after >2 years. After 18 months of grazing, there was no significant difference in the number of caterpillars on ungrazed (2.8 individuals/plot), lightly grazed (1.9–2.4 individuals/plot) or commercially grazed plots (2.3 individuals/plot). However, after 30 months, there were more caterpillars in the ungrazed plots (4.9 individuals/plot) than in the lightly grazed (1.9–2.4 individuals/plot) or commercially grazed plots (0.5 individuals/plot). From January 2003, four management regimes (no grazing; light grazing: sheep at 0.9 ewes/ha or sheep and cattle equivalent to 0.9 ewes/ha; commercial grazing: sheep at 2.7 ewes/ha) were replicated six times each in twenty-four 3.3-ha plots (in three pairs of adjacent blocks). Caterpillars were sampled by sweep net in 2003–2005.

(Summarised by: Andrew Bladon, edited from Farmland synopsis)