Riparian buffer strips: Their role in the conservation of insect pollinators in intensive grassland systems

There is growing concern that the global decline of insect pollinators will adversely influence the stability of pollination in agricultural and terrestrial ecosystems. By enhancing habitat heterogeneity and ecological connectivity, riparian buffer strips have the potential to promote insect pollinators in intensively managed landscapes. Insect pollinators and flowering plants were investigated on a range of riparian margins, and their adjacent grassland fields, to determine the main physical and botanical attributes driving pollinator diversity.Irrespective of whether they were fenced or not, riparian margins had richer plant assemblages and supported more pollinators than grassland fields. While the erection of fences did not enhance the richness or diversity of flowers, fenced riparian buffer strips supported more even and diverse assemblages of bumblebees and a greater number of butterflies than unfenced riparian margins. More bumblebees and butterflies were recorded in wide buffer strips (i.e. over 5m wide) than in unfenced margins or narrow buffer strips (i.e. ≤3.5m wide) and butterfly assemblages in wide buffer strips were richer and more diverse. There was a strong positive relationship between floral resources and the abundance, richness and diversity of bumblebee and butterfly assemblages. Pollinators only foraged on a small number of the flower species present and impacts of fencing and buffer strip width could not solely be attributed to the area and/or species richness of flowers.Fenced riparian buffer strips, particularly when over 5m wide, have the potential to provide resources for insect pollinators in intensively grazed systems. Management to enhance floristic diversity (to provide a more continuous supply of pollen and nectar) and tussock forming grasses (to provide shelter for pollinators and nesting locations for bumblebees) could further increase their value to insect pollinators. In grassland systems, restricted grazing is easier to implement than mowing. It is, however, important that grazing management does not unduly interfere with other ecosystem services derived from riparian buffer strips (e.g. diffuse pollution mitigation). Widespread fencing of watercourses at the catchment level could result in the simplification of these inherently dynamic and complex habitats. Buffer strips should therefore be strategically placed to optimise benefits such as ecological connectivity and diffuse pollution mitigation.