Beyond pollination – The neglected contribution of ground-nesting bees to soil functions

While the pollination services provided by wild bees are now well recognized, their importance as soil ecosystem engineers has been largely overlooked, despite the fact that most species nest in the soil in self-excavated burrows. Here we provide an overview of the many direct and indirect effects of ground-nesting wild bees on the physical, chemical and biological properties of soil, soil functions, and ecosystem services. In particular, we discuss how ground-nesting bees move and mix substantial amounts of soil during nest construction, thereby altering soil physical properties (e.g., soil pore architecture, soil porosity, density) and soil functions (e.g., water and gas exchange), and act as geomorphic agents at larger scales (affecting, e.g., surface runoff and soil erosion). We also review how ground-nesting bees affect soil chemical and biological properties through their nesting activity, leading to the redistribution and accumulation of organic carbon and nutrients in the soil, providing hotspots for microbial activity, and introducing a range of organisms into the soil. Furthermore, we discuss the large-scale indirect effects on soils through their pollination functions, which shape plant communities and soil functions modulated by plants. Lastly, we highlight the role of ground-nesting bees as soil ecosystem engineers that complement the activity of other bioturbators in both space and time by occupying biogeographical niches where other bioturbators are largely absent, and by complementary activity peaks during the season. We emphasize the distinctive position of ground-nesting bees among soil fauna, acting as both pollinators and soil bioturbators, and conclude that ground-nesting bees deserve greater attention and recognition in future research and conservation policy as part of soil biodiversity and for their role as soil ecosystem engineers.