Management to enhance pollen and nectar resources for bumblebees and butterflies within intensively farmed landscapes

Abstract

There have been serious global declines in diversity of bumblebees, butterflies and other pollinating insects. The most effective means of increasing abundance and diversity of bumblebees on farmland is to sow simple, low cost mixtures of dicotyledons rich in pollen and nectar, as prescribed under the UK agri-environment schemes. The potential benefits of this management prescription for butterflies are unknown. Similarly, more information is needed on how to manage this habitat to maximise the provision of pollen and nectar resources whilst protecting breeding habitat for butterflies. This study aimed to devise mixtures and cutting management regimes which address these issues. We found significant effects of seed mixture, timing and frequency of cutting, and removal of cut material on vegetation composition, flower resource availability and pollinators (the abundance, species richness and temporal distribution of butterflies and bumblebees, including males and queens, attracted to the mixtures). We recommend that nectar flower mixtures are refined by the inclusion of the best performing species to provide mid- and late-season forage resources (Trifolium spp., Lotus corniculatus and Centaurea nigra), and the removal of competitive grass species. Summer cutting in May or early June, with removal of herbage where possible, should be applied to half the patch to extend the flowering season, and minimise damage to butterfly breeding habitat. This should be accompanied by the typical autumn cut to the whole patch. Even with best management practice, such nectar flower mixtures are only effective for 3–4 years and this should be recognised in policies aimed at enhancing pollinator populations in agricultural landscapes.