Is there a benefit of excluding sheep from pastures at flowering peak on flower-visiting insect diversity?

Abstract

Permanent grasslands are an important habitat for insect communities, including pollinator populations which are in pan-European decline. Here, we investigated the benefits of temporarily excluding sheep from pastures on butterfly (Lepidoptera: Rhopalocera and Zygaenidae) and bumblebee (Hymenoptera: Bombidae) communities in two semi-natural grasslands differing in soil fertility and surrounding landscapes. We compared the impact of continuous grazing against rotational grazing (RG) at the same stocking rate but in which a subplot was excluded from the rotation during the main flowering period. We predicted that the diversity of flower-visiting insect community would be improved by RG due to the preservation of flower-rich patches and the maintenance of sward heterogeneity. Benefits of RG management were mainly evidenced on bumblebee density and species richness, with some additional effects on local density of butterflies during the subplot-exclusion period. Temporarily excluding sheep from pastures during peak flowering could thus offer an opportunity to preserve the diversity of flower-visiting insects, in spite of weaker benefits than could have been expected from previous surveys with cattle.