Restoration and management of machair grassland for the conservation of bumblebees

Abstract

Machair is a grassland habitat that supports nationally rare species including the bumblebee species Bombus distinguendus and Bombus muscorum. Changes in land management practices have resulted in a loss of floral diversity in some areas, reducing the availability of bumblebee foraging resources. In order to determine the most effective way of increasing forage plant availability on degraded machair, a restoration trial was established in western Scotland and comprised four seed mixes and a fallow treatment. Treatments were monitored over 3 years in order to compare the relative abundance of bumblebees and their forage plants. Two mixes contained wildflower species; one mix is currently used to create bird and bee foraging habitat on nature reserves and the fourth is a commercially available grass mix. There was little variation in inflorescence and bumblebee abundance between treatments early on but marked differences emerged later in the season in all 3 years. By the end of the monitoring period, the wildflower treatments contained between four and eighteen times more inflorescences than other treatment types. Similar trends were observed in bumblebee abundances. Some of the rarest bumblebee species exist primarily in areas that have largely escaped agricultural intensification. In these areas it is important that habitat management is specifically targeted and translated into appropriate agri-environment schemes. We suggest that the most effective method for restoring bumblebee forage plants on machair is to sow wildflower-rich seed mixes and this should be combined with late cutting and winter grazing practices to maintain sward diversity over time.