Vegetation-free areas encourage ground-nesting wild bees

New methods for conservation management of wild bees on calcareous grasslands investigated.

Relatively little is known about the nesting requirements of ground-nesting wild bees, although nesting sites are of central importance for the support of most wild bee species. Of the nearly 600 wild bee species in Germany, 75 percent nest in the soil, but studies to date have mainly focused on wild bee species nesting above ground in cavities. A research team from the University of Göttingen has now shown in a study on calcareous grasslands that the small-scale removal of vegetation led to a significant increase in ground nests, especially when there was an adjacent, high abundance of flowers. The results have been published in the journal Global Ecology and Conservation.

For the study, the scientists selected eight calcareous grasslands around Göttingen. -Calcareous grasslands are one of the most species-rich habitats in Central Europe and are therefore of crucial importance for the protection of bee diversity-, explains Annika HaÃ, postdoctoral researcher in the Functional Agrobiodiversity Unit at Göttingen University. To test whether ground-nesting wild bees prefer to build their nests in vegetation-free areas, the research team removed the vegetation cover on three plots per calcareous grassland of one square meter each. -The plots were very quickly accepted by the bees-, says first author Hanna Gardein, who now works as a doctoral student at the Institute for Bee Conservation at the Julius Kühn Institute in Braunschweig.

Overall, the number of bee nests was fourteen times higher on the plots compared to the control plots. The nesting activity was also significantly increased on the vegetation-free plots, especially at warm soil temperatures. -Through our study, we can make specific recommendations for creating such plots: Those who want to create such open-soil structures should preferentially establish them on warm, sunny slopes. Here we were able to determine a particularly high colonization. The wild bees also preferred nesting sites that were directly adjacent to flowering resources-, Gardein summarizes the results of her master’s thesis.

The importance of open soil areas for wild bees could also be confirmed by comparing the eight calcareous grasslands: More wild bees were recorded on the calcareous grasslands that had more open soil structures and flowering resources across the entire area. As expected, this was especially true for ground-nesting wild bee species. -Our study underlines the need to consider the availability of nesting resources in studies and projects promoting wild bees-, conclude Catrin Westphal and Teja Tscharntke, Functional Agrobiodiversity and Agroecology, University of Göttingen. -Small-scale removal of vegetation cover proved to be an easy-to-implement measure that can contribute significantly to the promotion of ground-nesting wild bees.â

Original publication: Gardein, H., Fabian, Y., Westphal, C., Tscharntke, T., & Hass, A. (2022). Ground-nesting bees prefer bare ground areas on calcareous grasslands. Global Ecology and Conservation, https://doi.org/10.1016/j.gecco.2022.e02289 .