Buzzing on top: Linking wild bee diversity, abundance and traits with green roof qualities
Kratschmer S., Kriechbaum M., Pachinger B.
Urban Ecosystems, 21:429–446
Urban Farm DB summary
Monthly surveys on nine Vienna green roofs in 2014 recorded 992 wild bees of 90 species. Forage availability and fine substrates strongly boosted diversity and abundance; ground-nesting social bees and Sedum bloom-period foraging shaped a distinct rooftop bee community.
Key points
- 1Wild bee diversity and abundance on green roofs are strongly enhanced by increased forage availability and fine substrates.
- 2The study observed 992 individuals belonging to 90 wild bee species across nine green roofs in Vienna.
- 3Bees on roofs were typically solitary, polylectic, and 8.3–11.2 mm, with a higher proportion of above-ground nesting bees compared to common species in Middle Europe.
- 4Ground-nesting wild bees, which were mainly eusocial and smaller (6.4–9.6 mm), benefited from roofs with fine and deeper substrates.
- 5Flowering Sedum species served as crucial forage resources during periods of low wildflower availability (e.g., June).
Extracted facts
7 factsOnly numbers and their conditions are stored, as structured data — never the source's own sentences. Metric and condition names stay in English, as coded.
- 992 individuals
wild bee individuals observed(green roof)
Biodiversityn = 9- region
- AT-Vienna
- setting
- urban-rooftop
- years
- 2014
- months
- March-September
- sites
- nine green roofs
- sampling
- monthly semi-quantitative
- 90 species
wild bee species richness(green roof)
Biodiversityn = 9- region
- AT-Vienna
- setting
- urban-rooftop
- years
- 2014
- months
- March-September
- sites
- nine green roofs
- 8.3–11.2 mm
body size(green roof wild bee)
Biodiversity- region
- AT-Vienna
- setting
- urban-rooftop
- years
- 2014
- group
- wild bees on roofs (solitary, polylectic)
- 6.4–9.6 mm
body size(ground nesting wild bee)
Biodiversity- region
- AT-Vienna
- setting
- urban-rooftop
- years
- 2014
- group
- ground-nesting wild bees, mainly eusocial
- 5–15 %
flower coverage(green roof)
Biodiversity- region
- AT-Vienna
- setting
- urban-rooftop
- years
- 2014
- month
- June
- label
- low forage availability by wildflowers
- strongly positively affected by forage and fine substrates↑ Increase
wild bee diversity and abundance(green roof)
Biodiversityn = 9Control: roofs with lower forage availability and coarser substrates- region
- AT-Vienna
- setting
- urban-rooftop
- years
- 2014
- predictors
- forage availability, fine substrates
- higher on green roofs↑ Increase
above ground nesting bee share(green roof)
BiodiversityControl: common species composition in Middle Europe- region
- AT-Vienna
- setting
- urban-rooftop
- years
- 2014
Direction of conclusions
Each author conclusion is recorded only as a coded direction per topic. Read the original for the conclusion itself.
- BiodiversitySupports
Abstract and stored text
OpenAlexGreen roofs are potentially valuable habitats for plants and animals in urban areas. Wild bees are important pollinators for crops and wild plants and may be enhanced by anthropogenic structures, but little is known about wild bees on green roofs in cities. This study investigates the effects of green roof qualities (floral resources, substrate character and depth, roof height and age) on wild bee diversity, abundance and traits (nesting type, sociality, pollen specialisation, body size) on green roofs in Vienna. Nine green roofs were sampled monthly between March and September 2014 by a semi quantitative approach. Wild bees were collected in pre-defined sub-areas for the same amount of time and floral resources were recorded. Over all green roofs, 992 individuals belonging to 90 wild bee species were observed. Wild bee diversity and abundance was strongly positively affected by increasing forage availability and fine substrates. Wild bees on roofs were characteristically solitary, polylectic and 8.3–11.2 mm. Regarding nesting type, the percentage of above-ground nesting bees was higher compared to the common species composition in Middle Europe. Ground-nesting wild bees were mainly eusocial, smaller (6.4–9.6 mm) and positively affected by roofs with fine substrates. During June, when forage availability by wildflowers on roofs was “low” (5–15% flower coverage), flowering Sedum species were an important forage resource. We conclude that wild bee diversity and abundance on green roofs are enhanced by floral resources. Furthermore, the installations of areas with finer and deeper substrates benefit ground nesting and eusocial wild bees.
Why it matters for urban farming
This research shows that urban farms with green roofs can significantly boost local wild bee populations by providing abundant floral resources and suitable nesting substrates. For urban farmers, this means carefully selecting plants that offer continuous blooms throughout the season, especially during lean periods, and considering the use of fine, deeper substrates to support ground-nesting bees. Enhancing bee habitats directly contributes to better pollination for urban crops and overall urban biodiversity.