Wild bee communities benefit from temporal complementarity of hedges and flower strips in apple orchards

Wild bees importantly pollinate both crop and wild plants. Yet, in intensive agricultural landscapes, wild bees are rare due to resource limitations of nectar and pollen. Flower strips and hedges are often used as resource enhancements for wild bees to overcome this shortage, but provide floral resources only during specific time periods. To sustain diverse and stable bee communities, bee-attractive flowers need to be available during the entire growing season. This may be achieved by combining flower strips and hedges to complement each other and provide continuous floral resources. Over three subsequent years, we compared the phenology of flower and wild bee communities in perennial flower strips, hedges and improved hedges (complemented with a sown herb layer) in conventional apple orchards in Southern Germany, a pollination-dependent crop system. Hedges provided floral resources in the early season while the flower strips took over later in the season. Bees visited the hedges mostly from March to June, whereas they visited the flower strips from June to August in the first year, and in the second year already from April onwards. Flower strips were visited with an overall higher abundance and species richness than both the hedges and the improved hedges. Synthesis and application. For enhancing wild bees in intensive apple orchards, hedges and perennial flower strips are complementary in providing flower resources. Yet, flower strips bloom more constantly and during periods of flower scarcity, and thus attract a higher diversity of bees than hedges. Perennial flower strips of different age classes should be preferred over annual strips, at best in a network with some well-maintained hedges, as perennial flower strips of different age attract different bee communities and thus potentially a higher bee diversity on the landscape level.