Enhancing floral resources for pollinators in productive agricultural grasslands

Abstract

Across N.W. Europe intensive agricultural management has increased productivity to the detriment of floral resources vital for insect pollinators like bees, butterflies and hoverflies. While the creation of wildflower habitats has been widely used to re-establish such resources into arable ecosystems (e.g. sown into field margins), comparable low cost methods for enhancing floristic diversity in production grasslands are lacking. We investigated how simple and cheep seed mixtures based around three plant functional groups (grasses, legumes and non-leguminous forbs) could be used to enhance flowering resources to benefit insect pollinator communities over a four year period. We demonstrate that the abundance and species richness of pollinators was correlated with the increased availability of legume and non-legume forb flowers. While the flowering resources provided by agricultural cultivars of legumes declined rapidly once sown, the inclusion of a forb component within seed mixtures was effective in increasing the long-term persistence of these resources. As a result the abundance and species richness of insect pollinators over the four years showed greater stability where forbs were also sown. Sward management also played a role in the persistence of floral resources, with grazing more likely to maintain legume cover than cutting. In conclusion, we demonstrate that low cost seed mixtures can be used to enhance floristic diversity to benefit pollinators, although the continued value of these grasslands over time is dependent on complementarity between sown legumes and forbs. As permanent grassland covers c. 40% of the UK the enhancement of their floristic diversity has a huge potential to benefit insect pollinators. The type of land sharing approaches suggested here maintain modest agricultural productivity and so may be the most likely to achieve benefit to pollinators through wide-scale farmer uptake.