Agroforestry can enhance foraging and nesting resources for pollinators with focus on solitary bees at the landscape scale

Mosaics of agricultural land, forests, and other semi-natural areas represent landscapes providing valuable habitats and resources for various insect groups. We investigated the added value of agroforestry, the combination of crops or grasslands with woody elements, for important pollinating insects e.g. wild bees and associated pollination service potential at the landscape scale using a modelling approach. In a case study region in Switzerland, characterized by traditional grassland-cherry agroforestry, eight 1 km2 landscape test sites (LTS) with contrasting coverage of agroforestry were selected. Flowering resources and potential nesting habitats were mapped. The contribution of cherry trees floral resources was estimated by flower counts. Lonsdorf equations were used to assess the pollination service potential and were modelled at landscape scale for three scenarios: (A) agroforestry systems containing flowering cherry trees, (B) agroforestry systems with tree species that do not provide floral resources to wild bees and (C) replacement of agroforestry by grassland systems without trees. In total there was a higher proportion of flowering and nesting resources in LTS with agroforestry. The area of cherry flowers was, on average, a factor of 1 to 2.7 of the canopy area. Models predict enhanced wild bee habitat quality and tend to predict increased provision of pollination services by wild bees in landscapes with higher proportion of cherry tree agroforestry. Mainly cavity nesting species might potentially benefit from the agroforestry trees. Our findings highlight the potentially important role of traditional flowering fruit tree with grassland agroforestry in sustaining wild bees and associated delivery of pollination services in agroecosystems.