Pollinator habitat enhances nesting opportunities for wild bees

        Wild bees require reliable floral and nesting resources, both of which are degraded by agricultural intensification. Wildflower plantings are well documented to provide floral resources for bees. However, empirical tests of their ability to promote critical nesting habitat are limited. Moreover, the key attributes that favor bee nesting are poorly known. We tested the ability of wildflower plantings to increase nesting of native soil-nesting bees in agricultural landscapes in Northern California. We also quantified whether differences in vegetation and edaphic characteristics between wildflower plantings and unplanted control sites affected nesting. We monitored nesting over three seasons in replicated wildflower plantings and paired control sites using emergence trapping. At each trap location we also surveyed vegetation and edaphic characteristics. We tested differences in nest density and species richness of soil-nesting bees using GLMM. Bee communities, vegetation and soil characteristics were summarized using NMDS and differences compared between wildflower plantings and control sites using permutational ANOVA.
        In the first year of establishment nest density and species richness of nesting bees were significantly greater in wildflower plantings than control sites. Higher nest density and species richness were maintained in the second and third year, but they did not increase relative to the first year. These results suggest that wildflower plantings provide immediate nesting benefit for bees in such landscapes. Vegetation cover and surface characters differed strikingly at wildflower plantings. These habitat differences coupled with differences in bee nesting, suggest potential strategies to encourage native soil-nesting bees and promote pollinator biodiversity within agricultural landscapes.