A comparison of bee communities of Chicago green roofs, parks and prairies

Due to loss of natural habitats, human-dominated green spaces are likely to increase in importance for biodiversity support. We assessed the potential value of urban "green roofs" for native pollinator conservation in the Chicago region, comparing them with reference habitats of tallgrass prairie natural areas and traditional city-park green spaces. We found that native bees are present on green roofs, though at lower abundance and diversity than in reference habitats. Green-roof and prairie bee communities were distinct from each other, while those in parks were intermediate and similar to the other two habitat types. Bee-community patterns were related to habitat characteristics at both the site and landscape scales. Overall, bee abundance and species richness increased with greater proportions of green space in the surrounding landscape. However, this relationship disappeared in cases where green space was dominated by turf grass. At the site scale, bees benefited from greater plant diversity, and bee and plant-community composition were significantly correlated. Green roofs are potentially valuable sites for bee conservation in urban areas, particularly if planted with diverse native forbs to provide foraging resources, and designed to accommodate bees with different nesting habits.