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Grassland extensification enhances nest densities of ground-nesting wild bees

Albrecht, Matthias1; Bossart, Stefanie1; Tschanz, Philippe1; Keller, Thomas1; Sutter, Louis1

Published Oct 04, 2023 on Dryad. https://doi.org/10.5061/dryad.9ghx3ffpn

Cite this dataset

Albrecht, Matthias et al. (2023). Grassland extensification enhances nest densities of ground-nesting wild bees [Dataset]. Dryad. https://doi.org/10.5061/dryad.9ghx3ffpn

Abstract

  1. Ground-nesting wild bees provide essential pollination services in agroecosystems, but they are jeopardized by intensive agricultural management. To mitigate such negative impacts, agri-environment schemes have been implemented. While the success of enhancing floral food resources is relatively well studied, the role of agri-environmental schemes in providing suitable nesting habitat remains underexplored.
  2. We studied the effectiveness of meadow extensification according to the Swiss agri-environment scheme in promoting nesting of ground-nesting bees. Using a paired design, we quantified their nests during four rounds (March-June) in pairs of nine randomly selected extensively (i.e. no fertilizer input, postponed first mowing) and nine intensively managed meadows with similar soil properties, slope, exposure and landscape context. Nest numbers and vegetation characteristics were surveyed in areas of 250 m2. Vegetation properties were also assessed in 0.5 m × 0.5 m plots around nest locations and randomly selected locations without nests within each meadow to assess their role as drivers of nesting incidence (nest presence/absence) at this plot scale.
  3. We found substantially higher nest numbers of ground-nesting bees in extensively (mean ± SE per sampling round = 46.8 ± 14.2) compared to intensively managed meadows (0.8 ± 0.3; no nests in three out of nine intensively managed meadows). Extensively managed meadows harboured nests of several dominant crop pollinator species, including aggregations of e.g. Lasioglossum malachurum contributing to high nest densities in some of them. Number of nests was negatively related to grass cover and vegetation height, which were lower in extensively compared to intensively managed meadows. Plot-level nesting incidence increased with bare ground and moss cover, and decreased with grass cover.
  4. Synthesis and applications. Our study shows that extensively managed meadows are better nesting habitats for ground-nesting bees than intensively managed meadows, if reduced management intensity is associated with altered vegetation characteristics such as reduced grass cover and vegetation height, and small-scale availability of bare ground, driving these effects. This highlights that maintaining and promoting extensive management of meadows can promote ground-nesting wild bees, including dominant crop pollinators, not only by enhancing floral resources but also by improving nesting opportunities in agroecosystems.

README: Grassland extensification enhances nest densities of ground-nesting wild bees

https://doi.org/10.5061/dryad.9ghx3ffpn

Data on (1) nest densities of ground-nesting bees in extensively and intensively managed meadows, (2) captured bee species, (3) vegetation characteristics assessed in vegetation plots, (4) soil texture, soil organic carbon content and soil organic matter, as well as (5) soil bulk density are provided in separate data files. All variables and abreviations are explained below. All methods to collect and analyse the data are described in detail in the methods section of the article.

Description of the data and file structure

(1) Nest density per sampling round (nestcount_per_round.csv):

Data containing information on the numbers of ground-nesting bee nests found within the 250 m2 sampling area per sampling round.

  • field_id: Unique field identifier ([field_id]_[management])
  • pair: Meadow pair ID
  • management: Meadow management intensity (extensive, intensive)
  • round: Sampling round

(2) Captured bees (bees.csv):

Data containing information on the captured bee species.

  • species: Species name of the captured specimen
  • genus: Genus name of the captured specimen
  • field_id: Unique field identifier ([field_id]_[management])
  • pair: Meadow pair ID
  • management: Meadow management intensity (extensive, intensive)

(3) Vegetation characteristics (vegetation.csv):

Data containing the results from the vegetation assessments taken at nest and control plots.

  • field_id: Unique field identifier ([field_id]_[management])
  • pair: Meadow pair ID
  • management: Meadow management intensity (extensive, intensive)
  • round: Sampling round
  • type: Whether the soil sample was taken at the nest (nest) or randomly selected control location (control)
  • nest_pa: nest presence/absence, same as type but coded as 0/1
  • cov_bare_ground: Bare ground cover (%)
  • cov_herbs: Herbaceous vegeation cover (%)
  • cov_grass: Grass cover (%)
  • cov_moss: Moss cover (%)
  • cov_litter: Litter cover (%)
  • veg_height: Vegetation height (cm)

(4) Soil texture, soil organic carbon content, soil organic matter (soil_texture.csv):

Data containing the results from mixed soil sample analysis.

  • field_id: Unique field identifier ([field_id]_[management])
  • pair: Meadow pair ID
  • management: Meadow management intensity (extensive, intensive)
  • soc: Soil organic carbon content (%)
  • som: soil organic matter content (%)
  • soil_sand: sand content (%)
  • soil_silt: silt content (%)
  • soil_clay: clay content (%)

(5) Soil bulk density (soil_density.csv):

Data containing the results from the soil dry bulk density analysis from cylindrical soil cores.

  • field_id: Unique field identifier ([field_id]_[management])
  • pair: Meadow pair ID
  • management: Meadow management intensity (extensive, intensive)
  • bulk_density: soil dry bulk density (g\cm3)

Methods

For a detailed description of the methods used to collect and analyse this data please see methods section of the article.

Funding

Swiss National Science Foundation, Award: 185273