From species to landscape: Quantification of nectar and pollen reveals seasonal gaps for pollinators in intensive arable systems

The diversity and abundance of pollinators are decreasing globally, particularly in agricultural landscapes. Reduction of floral resources is one of the main causes, as nectar and pollen must be continuously and sufficiently available throughout the period of pollinator activity in a landscape. Nectar and pollen production at local and landscape levels and their phenology in relation to pollinator abundance remain poorly understood. Over the growing season (April to August), we surveyed flower-pollinator interactions for three years, in 10 intensively managed agricultural landscapes in France. Surveys covered eight types of landscape elements – forest edges, mass-flowering crops, hedgerows, road verges, grasslands, fallows, flower strips, and field margins – yielding 5612 flower-pollinator interactions. We quantified the dynamics of nectar and pollen production over the growing seasons in the landscape elements and assessed effects of resource availability on pollinator abundance at local and landscape levels. The seasonal dynamics of floral resource production differed among the landscape elements. Considering the cover of these elements in the landscapes, nectar and pollen resources peaked in April and then decreased continuously until August at the landscape level. Floral resources met pollinator needs more effectively in April-May but became more limiting thereafter, especially in June. These results highlight a temporal mismatch between resource supply and demand, suggesting that targeted habitat management in June could improve pollinator conservation greatly.