Effects of flowering cover crops and landscape heterogeneity on native bee diversity in vineyards

Expansion of vineyards in California’s North Coast wine grape growing region have fragmented oak woodland habitats and reduced the amount of floral resources available to native bees. Increasing floral diversity in vineyards may provide resources for native bees and reduce the negative effects of this habitat fragmentation. Some have theorized that landscape context will determine native bee response to localized, on-farm diversification practices. In this study, native bees were collected from paired vineyard plots with and without flowering summer cover crops. In order to evaluate the interaction between landscape and field-scale habitat diversity, the vineyard sites were located along a continuum of landscape diversity (ranging from low to high diversity). Flowering cover crop species included Phacelia tanacetifolia, Ammi maujus, and Daucus carota. At peak bloom, the flowers were sampled for native bees, at the same time bees were collected from grasses and weedy vegetation in the paired control plots. Relative to the weedy vegetation in control plots, the flowering cover crops attracted a more diverse and abundant set of native bees. Native bee populations on the flowers also appeared to be influenced by changes in landscape heterogeneity, although the influence varied for each species of flower.