Crop diversification for pollinator conservation

Context: Intensive agriculture drives insect decline impacting insect-mediated ecosystem services that support production. Crop diversification shows promise in increasing crop productivity and enhancing ecosystem services, however, the impact on biodiversity conservation, particularly of pollinators, is unclear. Objectives: Here, we synthesize the mechanisms and current evidence base of how increasing the spatial and temporal diversity of crops within and across agricultural fields can benefit pollinator biodiversity. Methods: We focus on research in the highly intensified agricultural regions, in Western Europe and North America, from which we know a lot about pollinator decline, but use inspiration from tropical regions. Results: We find that higher crop diversity, with sequentially flowering cultivars, intercropping practices, and a larger coverage of flowering crops, for example through integrating the cultivation of forgotten, novel, and woody crops increases flower resource availability throughout the active flight period of pollinators. All practices can increase landscape heterogeneity, which is further enhanced by decreasing field sizes. As a result, the functional connectivity increases, which improves the flower accessibility within the foraging ranges of pollinators. Conclusions: Our review highlights the potential benefit of various crop diversification measures for supporting pollinating insects without taking land out of production, as well as the limitations, including that only a subset of pollinator species may benefit. Empirical evidence suggest that diversification practices could benefit pollinators, but landscape-wide studies are needed to properly evaluate the true potential of crop diversification for pollinator conservation as part of the solution for bending the curve of pollinator decline.