Grazing intensity and the diversity of grasshoppers, butterflies, and trap-nesting bees and wasps

Reduce grazing intensity on pastures

In a comparison of six intensively (5.5 cattle/ha) and six lightly (1.5 cattle/ha) cattle-grazed meadows with six ungrazed meadows in Germany, meadows with light grazing had a greater number of individual cavity-nesting bees, wasps and their brood parasites than meadows with intensive grazing  (Kruess & Tscharntke 2002). There was an average of 47 emerging individuals/lightly grazed site, compared to 27 emerging individuals/intensively grazed site. Reduced intensity of grazing did not significantly increase the number of bee and wasp species.

Increase grazing intensity or cutting frequency on grassland

A replicated, site comparison study in 1996 in 18 grasslands in Schleswig-Holstein, Germany (Kruess and Tscharntke 2002) found that species richness and abundance of adult butterflies and burnet moths at intensively grazed sites was lower than at sites with low or no grazing, but the responses of caterpillar richness and abundance to grazing intensity were mixed. Butterfly species richness and abundance were lower at intensively grazed sites (average richness = 2; average abundance = 1 ) than low intensity grazing (average richness = 4; average abundance = 8) and ungrazed (average richness = 7; average abundance = 21) sites. Caterpillar species richness was statistically similar in intensively grazed (average = 2) and low intensity grazing (average = 4) sites, but lower in both than in ungrazed sites (average = 7). Caterpillar abundance was statistically similar between intensively grazed (average = 1) and low intensity grazed (average = 9) sites, but intensively grazed sites had lower abundance than ungrazed sites (average = 12). Intensively grazed sites (6) had an average stocking density of 1.4 cattle/ha annually from May–November, low intensity grazed sites (6) had an average density of 5.5 cattle/ha annually from April–October, and ungrazed sites (6) had not been stocked for 5–10 years. From May–September 1996, at each site separate transect walks were conducted once monthly for adult butterflies and burnet moths (45-minute transects) and caterpillars (45-minute transects in grazed sites and 60-minutes in ungrazed sites).

(Summarised by: Eleanor Bladon)

Reduce grazing intensity on grassland by reducing stocking density

A replicated, site comparison study in 1996 in 18 grasslands in Schleswig-Holstein, Germany (Kruess and Tscharntke, 2002) found that the species richness and abundance of adult butterflies and burnet moths at sites grazed at low intensity was higher than at intensively grazed sites and similar to ungrazed sites, but the responses of caterpillar richness and abundance to grazing intensity were mixed. Butterfly and burnet moth species richness and abundance were higher at low intensity grazing (average richness: 4; average abundance: 8) and ungrazed (average richness: 7; average abundance: 21) sites than at sites which were intensively grazed (average richness: 2; average abundance: 1). Caterpillar species richness was statistically similar at low intensity grazing (average: 4) and intensively grazed sites (average: 2), but lower in both than in ungrazed sites (average: 7). Caterpillar abundance was statistically similar in low intensity grazed sites (average: 9) and both intensively (average: 1) and ungrazed (average: 12) sites, but ungrazed sites had higher abundance than intensively grazed sites. Intensively grazed sites (6) had an average stocking density of 1.4 cattle/ha annually from May–November, low intensity grazed sites (6) had an average density of 5.5 cattle/ha annually from April–October, and ungrazed sites (6) had not been stocked for 5–10 years. From May–September 1996, at each site separate transect walks were conducted once monthly for adult butterflies and burnet moths (45-minute transects) and caterpillars (45-minute transects in grazed sites and 60-minutes in ungrazed sites).

(Summarised by: Eleanor Bladon)

Cease grazing on grassland to allow early succession

A replicated, site comparison study in 1996 in 18 grasslands in Schleswig-Holstein, Germany (Kruess and Tscharntke 2002) found that adult butterfly and burnet moth species richness and abundance and caterpillar abundance at ungrazed sites was higher than at intensively grazed sites but similar to low intensity grazed sites, and caterpillar species richness was higher at ungrazed sites than low and intensively grazed sites. Butterfly species richness and abundance and caterpillar abundance were higher at ungrazed (butterflies: average richness = 7, average abundance = 21; caterpillars: average abundance = 12) than intensively grazed (butterflies: average richness = 2, average abundance = 1; caterpillars: average abundance = 1) sites, but statistically similar between ungrazed and low intensity grazing (butterflies: average richness = 4, average abundance = 8; caterpillars: average abundance = 9) sites. Caterpillar species richness was higher at ungrazed sites (average = 7) than low (average = 4) and high intensity grazing (average = 2) sites. Intensively grazed sites (6) had an average stocking density of 1.4 cattle/ha annually from May–November, low intensity grazed sites (6) had an average density of 5.5 cattle/ha annually from April–October, and ungrazed sites (6) had not been stocked for 5–10 years. From May–September 1996, at each site separate transect walks were conducted once monthly for adult butterflies and burnet moths (45-minute transects) and caterpillars (45-minute transects in grazed sites and 60-minutes in ungrazed sites).

(Summarised by: Eleanor Bladon)

Reduce grazing intensity on grassland (including seasonal removal of livestock)

A replicated comparison of six intensively (5.5 cattle/ha) and six lightly (1.5 cattle/ha) cattle-grazed meadows with six ungrazed meadows in Germany (Kruess & Tscharntke 2002) found that meadows with light grazing had a greater number of individual cavity-nesting bees, wasps (Hymenoptera) and their brood parasites than meadows with intensive grazing. There was an average of 47 emerging individuals/lightly grazed site, compared to 27 emerging individuals/intensively grazed site. Reduced intensity of grazing did not significantly increase the number of bee and wasp species. Both abundance and total species richness of these insects were significantly higher on ungrazed grassland (11.5 species) than on intensively (4.7 species) or lightly (6.2 species) grazed pastures. These results were linked to an increase in vegetation height as grazing intensity is reduced.