Action: Create patches of bare ground for ground-nesting bees
One replicated controlled trial in Germany and four small trials (three replicated, one not) have shown that artificially exposed areas of bare soil can be successfully colonised by ground-nesting solitary bees and wasps in the first or second year. We have captured no evidence for the effect of creating areas of bare ground on bee populations or communities on a larger scale.
Supporting evidence from individual studies
Three scrapes with vegetation removed at Headley Heath, Surrey, England were being used by ground-nesting bees two or three years after they were created (Edwards 1996). The average densities of burrows attributed to ground-nesting bees and wasps were 2.3, 1.2 and 2.3 burrows/m2 for small (500 m2), medium (2,500 m2) and large (5,000 m2) scrapes respectively.
Nest density of ground-nesting bees and wasps was increased by removing plant cover, or digging and raising soil, in trial plots at five sandy grassland sites in Baden-Württemberg, southwest Germany in 1992, relative to five control sites (Wesserling & Tscharntke 1995). Digging and raising soil was more effective at increasing nest density. Raking was not very effective, because it generated a dense plant cover.
A study of artificially made scrapes on three lowland heaths in West Sussex, England (Edwards 1998) found between two and eight solitary bee species using the scrapes one to four years after they were created, with up to five of the species actively nesting.
Severns (2004) created 1 m2 plots of mostly bare ground whilst planting seeds of the endangered legume Kincaid's lupine Lupine sulphureus spp. kincaidii, in an upland prairie restoration project in Oregon, USA. The bare ground was colonised by an increasing number of nesting solitary bees, mostly of the common species Lasioglossum anhypops, over the following three years. Three years later, there were 320 nests over 30 plots.
Four shallow bays (3 x 5 m), with a rear vertical face (30 cm), were dug to attract ground-nesting bees and wasps at Shotover Hill, a heath degraded due to a long-term lack of grazing in Oxfordshire, southern England. All four bays were colonised in the first year with 80 solitary bee and wasp species recorded in the following three years (Gregory & Wright 2005).
- Edwards M. (1996) Entomological survey and monitoring, Headley Heath, 1995-1996. Unpublished report commissioned by The National Trust, 1995-1996
- Wesserling J. & Tscharnkte T. (1995) Habitatwahl von bodennistenden Wildbienen und Grabwespen - Pflegemassnahmen im Experiment (Habitat selection of bees and digger wasps - experimental management of plots). Mitteilungen der Deutschen Gesellschaft für allgemeine und angewandte Entomologie, 697-701
- Edwards M. (1998) Monitoring of bare ground for use by heathland insects. Unpublished report to the West Sussex Heathlands Project
- Severns P. (2004) Creating bare ground increases presence of native pollinators in Kincaid's lupine seeding plots (Oregon). Ecological Restoration, 22, 234-235
- Gregory S. & Wright I. (2005) Creation of patches of bare ground to enhance the habitat of ground-nesting bees and wasps at Shotover Hill, Oxfordshire, England. Conservation Evidence, 2, 139-141