Enhancing pollinator biodiversity in intensive grasslands

Undersow spring cereals, with clover for example

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that annually sown plots of spring barley Hordeum vulgare undersown with a mix of grasses and legumes had a higher abundance and species richness of butterflies, but a lower abundance of caterpillars, than grassland plots. In the first two years, undersown plots had a higher abundance (4–6 individuals/transect) and species richness (2–4 species/transect) of adult butterflies than extensively (abundance: 3–5 individuals/transect; richness: 2 species/transect) or conventionally managed (abundance: 1–2 individuals/transect; richness: 1 species/transect) grassland. However, there were fewer caterpillars in the sown plots (0–3 caterpillars/transect) than the extensively (1–8 caterpillars/transect) or conventionally managed (0–7 caterpillars/transect) grassland. In April 2002, experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. There were eight treatments, with three replicates/farm. The sown treatment comprised barley undersown with seven grasses and five legumes. Two extensive grassland treatments had minimal disturbance during summer and five conventional grassland treatments included modifications to conventional silage management (reducing fertilizer application, cutting and grazing). From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).

(Summarised by: Andrew Bladon)

Raise cutting height on grasslands

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that plots of intensively managed grassland cut to 10 cm in May and July did not have a higher abundance or species richness of butterflies, or abundance of caterpillars, than plots cut to 5 cm. On plots cut to 10 cm, the abundance (1–2 individuals/transect) and species richness (1 species/transect) of butterflies, and the abundance of caterpillars (0–5 caterpillars/transect), were not significantly different from plots cut to 5 cm (butterfly abundance: 0–2 individuals/transect; richness: 0–1 species/transect; caterpillar abundance: 0–4 caterpillars/transect). In April 2002, six experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. All plots were fertilized (225 kg nitrogen/ha, 22 kg phosphorus/ha, 55 kg potassium/ha), cut twice/year in May and July, and grazed in September. Three plots/farm were cut to 10 cm, and three were cut to 5 cm. From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).

(Summarised by: Andrew Bladon)

Delay cutting or first grazing date on grasslands to create variation in sward height

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that grassland plots cut in July had a higher abundance and species richness of butterflies, and abundance of caterpillars, than plots cut in May in only one out of four years. In the second year of management, the abundance of caterpillars on plots cut in July (6 caterpillars/transect) was higher than on plots cut in May (2 caterpillars/transect), but in other years there was no significant difference (July: 1–8; May: 0–5 caterpillars/transect). In the third year, the abundance (4 individuals/transect) and species richness (2 species/transect) of butterflies on plots cut in July was higher than on plots cut in May (abundance: 2 individuals/transect; richness: 1 species/transect), but both abundance and richness were similar in all other years (July: 1–5 individuals/transect, 1–2 species/transect; May: 1–3 individuals/transect, 1–2 species/transect). In April 2002, six experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. Three plots/farm were cut to 10 cm height in May, and three were cut to 10 cm height in July. From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).

(Summarised by: Andew Bladon)

Reduce grazing intensity on grassland by seasonal removal of livestock

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that plots of intensively-managed grassland without autumn cattle grazing did not have a greater abundance or species richness of butterflies, or abundance of caterpillars, than plots which were grazed. On intensively managed silage plots which were not grazed in September, the abundance (1–3 individuals/transect) and species richness (1 species/transect) of butterflies, and the abundance of caterpillars (0–7 caterpillars/transect), was similar to that on silage plots with September grazing (butterfly abundance: 0–2 individuals/transect; richness: 0–1 species/transect; caterpillar abundance: 0–4 caterpillars/transect). In April 2002, six experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. All plots were fertilized (225 kg nitrogen/ha, 22 kg phosphorus/ha, 55 kg potassium/ha) and cut twice/year to 5 cm in May and July. Three plots/farm were then grazed by cattle in September until the sward was 5–7 cm. The remaining plots were not grazed. From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).

(Summarised by: Andrew Bladon)

Reduce fertilizer, pesticide or herbicide use generally

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that unfertilized grassland plots had a similar abundance and species richness of butterflies, and abundance of caterpillars, to fertilized plots. On unfertilized plots, the abundance (1–4 individuals/transect) and species richness (1–2 species/transect) of butterflies, and the abundance of caterpillars (0–4 caterpillars/transect) were not significantly different from fertilized plots (butterfly abundance: 0–2 individuals/transect; richness: 0–1 species/transect; caterpillar abundance: 0–4 caterpillars/transect). In April 2002, six experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. All plots were cut to 5 cm twice/year in May and July, and grazed in September. Three plots/farm were fertilized (225 kg nitrogen/ha, 22 kg phosphorus/ha, 55 kg potassium/ha) and three were not fertilized. From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).

(Summarised by: Andrew Bladon)

Reduce the intensity of farmland meadow management

A randomised, replicated, controlled trial on four farms in southwest England (Potts et al. 2009) found that 50 x 10 m plots of permanent pasture managed more extensively without fertilizer or without grazing, and/or with a higher cutting height or reduced cutting frequency did not support more common bumblebees Bombus spp. than control plots conventionally managed for silage. There were twelve replicates of each management type, monitored over four years. No more than 2.2 bumblebees/transect were recorded on average on any grassy plot in any year.

Raise mowing height on grasslands to benefit farmland wildlife

A randomised, replicated, controlled trial from 2003 to 2006 in southwest England (Potts et al. 2009) (same study as (Defra 2007, Woodcock et al. 2007)) found plots of permanent pasture cut to 10 cm in May and July did not attract more butterflies (Lepidoptera), butterfly larvae or common bumblebees Bombus spp. than control plots cut to 5 cm. Experimental plots 50 x 10 m were established on permanent pastures (more than five-years-old) on four farms. There were nine different management types, with three replicates/farm, monitored over four years. Bumblebees and butterflies were surveyed along a 50 m transect line in the centre of each experimental plot, once a month from June to September annually. Butterfly larvae were sampled on two 10 m transects using a sweep net in April and June-September annually.

Plant wild bird seed or cover mixture

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that plots sown annually with mixes including wild bird seed had a higher abundance and species richness of butterflies, but a lower abundance of caterpillars, than grassland plots. In the first two years, plots sown with wild bird seed mixes had a higher abundance (4–10 individuals/transect) and species richness (2–4 species/transect) of adult butterflies than extensively (abundance: 3–5 individuals/transect; richness: 2 species/transect) or conventionally managed (abundance: 1–2 individuals/transect; richness: 1 species/transect) grassland. However, there were fewer caterpillars in the sown plots (0–3 caterpillars/transect) than the extensively (1–8 caterpillars/transect) or conventionally managed (0–7 caterpillars/transect) grassland. In April 2002, experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. There were nine treatments, with three replicates/farm. Two sown treatments comprised a mix of six crops and four legumes, or barley Hordeum vulgare undersown with seven grasses and five legumes. Two extensive grassland treatments had minimal disturbance during summer and five conventional grassland treatments included modifications to conventional silage management (reducing fertilizer application, cutting and grazing). From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).

(Summarised by: Andrew Bladon)

Reduce management intensity on permanent grasslands (several interventions at once)

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that plots of unfertilized, ungrazed grassland cut once in July or not cut during the summer had a higher abundance, but not species richness, of butterflies than fertilized silage plots cut twice/year. In extensive, unfertilized plots cut in July, or not cut all summer, the abundance of butterflies (1–6 individuals/transect) was higher than in intensively managed plots (0–4 individuals/transect), but the number of species was similar (extensive: 1–2; intensive: 0–2 species/transect). The number of caterpillars in extensive plots (1–8 caterpillars/transect) was higher than in one intensive treatment (0–4 caterpillars/transect), but did not differ significantly from other intensive treatments (0–7 caterpillars/transect). In April 2002, experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. There were seven treatments, with three replicates/farm. Three extensive treatments were not fertilized or grazed, and were either cut to 10 cm once/year in May or July, or topped in early spring and undisturbed in summer. Four intensive treatments included modifications to conventional silage management (reducing fertilizer application or grazing, or raising cutting height), but were all cut twice/year. From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).

(Summarised by: Andrew Bladon)

Plant nectar flower mixture/wildflower strips

A replicated, randomized, controlled study in 2002–2006 on four lowland farms in Devon and Somerset, UK (Potts et al. 2009) found that plots sown annually with mixes including legumes had a higher abundance and species richness of butterflies, but a lower abundance of caterpillars, than grassland plots. In the first two years, plots sown with legume mixes had a higher abundance (4–10 individuals/transect) and species richness (2–4 species/transect) of adult butterflies than extensively (abundance: 3–5 individuals/transect; richness: 2 species/transect) or conventionally managed (abundance: 1–2 individuals/transect; richness: 1 species/transect) grassland. However, there were fewer caterpillars in the sown plots (0–3 caterpillars/transect) than the extensively (1–8 caterpillars/transect) or conventionally managed (0–7 caterpillars/transect) grassland. In April 2002, experimental plots (50 × 10 m) were established on permanent pastures (>5-years-old) on four farms. There were nine treatments, with three replicates/farm. Two legume-sown treatments comprised barley Hordeum vulgare undersown with seven grasses and five legumes, and a mix of six crops and four legumes. Two extensive grassland treatments had minimal disturbance during summer and five conventional grassland treatments included modifications to conventional silage management (reducing fertilizer application, cutting and grazing). From June–September 2003–2006, butterflies were surveyed once/month on a 50-m transect through the centre of each plot. In April, June, July and September 2003–2006, caterpillars were counted (but not identified) on two 10-m transects/plot using a sweep net (20 sweeps/transect).

(Summarised by: Andrew Bladon)

Undersow spring cereals, with clover for example

A randomized, replicated, controlled trial from 2003 to 2006 in southwest England (Potts et al. 2009) (same study as (Defra 2007, Holt et al. 2010)) found plots on permanent pasture annually sown with a mix of legumes, or grass and legumes, supported more common bumblebees Bombus spp. (individuals and species) than seven grass management options. In the first two years, numbers of common butterflies (Lepidoptera) and common butterfly species were higher in plots sown with legumes than in five intensively managed grassland treatments. No more than 2.2 bumblebees/transect were recorded on average on any grass-only plot in any year, compared to over 15 bumblebees/transect in both sown treatments in 2003. Plots sown with legumes generally had fewer butterfly larvae than all grass-only treatments, including conventional silage and six different management treatments. Experimental plots 50 x 10 m were established on permanent pastures (more than five-years-old) on four farms. There were nine different management types, with three replicates/farm, monitored over four years. The two legume-sown treatments comprised either spring barley Hordeum vulgare undersown with a grass and legume mix (white clover Trifolium repens, red clover T. pratense, common vetch Vicia sativa, bird’s‐foot trefoil Lotus corniculatus and black medick Medicago lupulina) cut once in July, or a mix of crops including linseed Linum usitatissimum and legumes, uncut. Seven management types involved different management options for grass-only plots, including mowing and fertilizer addition. Bumblebees and butterflies were surveyed along a 50 m transect line in the centre of each experimental plot, once a month from June to September annually. Butterfly larvae were sampled on two 10 m transects using a sweep net in April and June-September annually.

Plant dedicated floral resources on farmland

A randomised, replicated, controlled trial on four farms in southwest England (Potts et al. 2009) found that 50 x 10 m plots of permanent pasture annually sown with a mix of legumes, or grass and legumes, supported more common bumblebees (individuals and species) than seven grass management options. There were twelve replicates of each management, monitored over four years. No more than 2.2 bumblebees/transect were recorded on average on any grassy plot in any year, compared to over 15 bumblebees/transect in both sown treatments in one year. The legumes sown included white clover Trifolium repens, red clover T. pratense, common vetch Vicia sativa and bird's-foot trefoil Lotus corniculatus.

Reduce chemical inputs in grassland management

A randomized, replicated, controlled trial from 2003 to 2006 in southwest England (Potts et al. 2009) (same study as (Defra 2007, Woodcock et al. 2007)) found plots of unfertilized permanent pasture cut just once in July or not cut at all during the summer attracted more adult butterflies (Lepidoptera), but not more butterfly species or common bumblebees Bombus spp. than control fertilized plots cut in May and July (managed for silage). Plots cut just once in May, plots cut twice either unfertilized or ungrazed, and plots with a higher cutting height did not support more adult butterflies than control plots. Caterpillars were more abundant in unfertilized plots cut just once in May or July, or not at all in summer, than in other treatments. None of the grass treatments supported more common bumblebee species or individuals than control plots. Experimental plots 50 x 10 m were established on permanent pastures (more than five-years-old) on four farms. There were nine different management types, with three replicates/farm, monitored over four years. Seven management types involved different management options for grass-only plots, including conventional silage practices, no cutting in summer, early summer cut (May), late summer cut (July), raised mowing height. Bumblebees and butterflies were surveyed along a 50 m transect line in the centre of each experimental plot, once a month from June to September annually. Butterfly larvae were sampled on two 10 m transects using a sweep net in April and June-September annually.

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

A randomized, replicated, controlled trial from 2003 to 2006 in southwest England (Potts et al. 2009) (same study as (Defra 2007, Woodcock et al. 2007)) found plots of permanent pasture managed without autumn/winter grazing did not attract more butterflies (Lepidoptera), butterfly larvae or common bumblebees Bombus spp. than control grazed plots. All plots were cut for silage in May and July. Grazed plots were grazed with cattle from September until the grass height was 5-7 cm. Experimental plots 50 x 10 m were established on permanent pastures (more than five years-old) on four farms. There were nine different management types, with three replicates/farm, monitored over four years. Bumblebees and butterflies were surveyed along a 50 m transect line in the centre of each experimental plot, once a month from June to September annually. Butterfly larvae were sampled on two 10 m transects using a sweep net in April and June-September annually.

Reduce management intensity on permanent grasslands (several interventions at once)

In the same randomized, replicated, controlled trial as (Defra 2007) from 2003 to 2006 on four farms in southwest England, (Potts et al. 2009) found plots of unfertilized permanent pasture cut just once in July or not cut at all during the summer attracted more adult butterflies (Lepidoptera) (but not more butterfly species or common bumblebees Bombus spp.) than control fertilized plots cut in May and July, managed as in conventional silage management. Plots cut just once in May, plots cut twice either unfertilized or ungrazed, and plots with a higher cutting height did not support more adult butterflies than control plots. Butterfly larvae were more abundant in unfertilized plots cut just once in May or July, or not at all in summer, than in other treatments. None of the grass treatments supported more common bumblebee species or individuals than control plots. No more than 2 bumblebees/transect were recorded on average on any grassy plot in any year. Experimental plots 50 x 10 m were established on permanent pastures (more than five-years-old) on four farms. There were nine different management types, with three replicates/farm, monitored over four years. Seven management types involved different management options for grass-only plots, including conventional silage practices, no cutting in summer, early summer cut (May), late summer cut (July), raised mowing height. Bumblebees and butterflies were surveyed along a 50 m transect line in the centre of each experimental plot, once a month from June to September annually. Butterfly larvae were sampled on two 10 m transects using a sweep net in April and June-September annually. This study was also part of the same study as (Pilgrim et al. 2007, Woodcock et al. 2007).

Plant wild bird seed or cover mixture

A randomized, replicated, controlled trial from 2003 to 2006 in southwest England (Potts et al. 2009) found plots on permanent pasture annually sown with a mix of legumes, or grass and legumes, supported more common bumblebees Bombus spp. (individuals and species) than seven grass management options. In the first two years, the numbers of common butterflies (Lepidoptera) and common butterfly species were higher in plots sown with legumes than in five intensively managed grassland treatments. No more than 2.2 bumblebees/transect were recorded on average on any grass-only plot in any year, compared to over 15 bumblebees/transect in both sown treatments in 2003. The plots sown with legumes generally had fewer butterfly larvae than all grass-only treatments, including conventional silage and six different management treatments. Experimental plots 50 x 10 m were established on permanent pastures (more than five-years-old) on four farms. There were nine different management types, with three replicates/farm, monitored over four years. Seven management types involved different management options for grass-only plots, including mowing and fertilizer addition. The two legume-sown treatments comprised either a mix of crops sown partly for wild birds, including linseed Linum usitatissimum and legumes, uncut, or spring barley Hordeum vulgare undersown with a grass and legume mix (white clover Trifolium repens, red clover T. pratense, common vetch Vicia sativa, bird’s?foot trefoil Lotus corniculatus and black medick Medicago lupulina) cut once in July. Bumblebees and butterflies were surveyed along a 50 m transect line in the centre of each experimental plot, once a month from June to September annually. Butterfly larvae were sampled on two 10 m transects using a sweep net in April and June-September annually. This study was part of the same experimental set-up as (Defra 2007, Pilgrim et al. 2007, Holt et al. 2010).

Plant nectar flower mixture/wildflower strips

A randomized, replicated, controlled trial from 2003 to 2006 in southwest England (Potts et al. 2009) (same experimental set up as Pilgrim et al. 2007) found plots on permanent pasture annually sown with a mix of legumes, or grass and legumes, supported more common bumblebees Bombus spp. (individuals and species) than seven grass management options. In the first two years, there were more common butterflies (Lepidoptera) and common butterfly species in plots sown with legumes than in five intensively managed grassland treatments. No more than 2.2 bumblebees/transect were recorded on average on any grass-only plot in any year, compared to over 15 bumblebees/transect in both sown treatments in 2003. Plots sown with legumes generally had fewer butterfly larvae than all grass-only treatments, including conventional silage and six different management treatments. Experimental plots 50 x 10 m were established on permanent pastures (more than five-years-old) on four farms. There were nine different management types, with three replicates/farm, monitored over four years. Seven management types involved different management options for grass-only plots, including mowing and fertilizer addition. The two legume-sown treatments comprised either barley Hordeum vulgare undersown with a grass and legume mix (including white clover Trifolium repens, red clover T. pratense, and common vetch Vicia sativa) cut once in July, or a mix of crops (including linseed Linum usitatissimum) and legumes, uncut. Bumblebees and butterflies were surveyed along a 50 m transect line in the centre of each experimental plot, once a month from June to September annually. Butterfly larvae were sampled on two 10 m transects using a sweep net in April and June-September annually.