Assessing the effectiveness of pollinator gardens for bee conservation along an urban-rural gradient

With growing awareness of global declines in bee populations, bee conservation has received increased attention from governmental agencies, nonprofit organizations, researchers, and the public. One popular strategy involves pollinator garden registration programs that certify gardens meeting required habitat provisioning criteria to motivate gardeners to provide high-quality food and nesting resources. While considerable financial and human resources are directed toward these programs and there are now over 1 million pollinator gardens registered globally, limited research has been conducted to verify their effectiveness for bee conservation. We compared bee abundance and richness in pollinator gardens, ornamental gardens, and lawns on an urban-rural gradient in the Greater Chicago Area, Illinois, USA. Our results suggest that pollinator gardens may support bee conservation by providing important floral resources. Pollinator gardens contained a higher flower density, a greater proportion of native flowers, and a greater proportion of flowers that provide nectar resources than ornamental gardens or lawns. Additionally, we observed more bees visiting pollinator gardens than ornamental gardens or lawns, a pattern that was consistent across the full urban-rural gradient. While pollinator gardens contained an increased abundance and richness of all groups of bees considered, the benefit appeared to be most pronounced for honey bees. Based on these results, we suggest that a continued emphasis on pollinator garden registration programs may be an effective strategy for bee conservation but recommend an increased focus on wild bees.