PhD defence: Hjalte Ro-Poulsen

Hjalte Ro-Poulsen defends his thesis,

Wild bees and honey bees in semi-natural habitats of Denmark;
Effects of beekeeping and management in grasslands and heathlands

Head of Section Inger Kappel Schmidt, IGN, Denmark
Professor Toke Thomas Høye, Aarhus University, Denmark
Senior Researcher Yoko Luise Dupont, Aarhus University, Denmark

Assessment committee:
Head of Department, PhD, Anders Nielsen, Norwegian Institute of Bioeconomy Research
Senior Researcher Per Kryger, Aarhus University, Denmark
Professor Lene Rostgaard Nielsen (Chair), IGN, Denmark

Bees are in decline, primarily attributed to loss of habitat. Fragmented habitats persist in an agricultural landscape, vulnerable to abandonment and surrounding stressors. Among stressors, concerns have been raised that managed honey bees (Apis mellifera) may competitively displace wild bees in protected areas. The main objective of this thesis was to investigate whether beekeeping pose a risk to wild bee communities in protected areas of Denmark, specifically semi-natural grasslands and heathlands. Central to this thesis is conservation of wild bees and additional research objectives involve how management of these habitats affect bees and other insects compared to abandonment.
The papers present the diverse bee assemblages of semi-natural grassland and heathlands, investigated using different survey methods. Furthermore, the occurrence of wild bees and effects of beekeeping, management and edaphic factors were investigated. The studies cover a temporal scale to elucidate the seasonal variation in floral resources and occurrence of wild bees and honey bees in from May until August.
Management of semi-natural areas had a positive effect on bee assemblages through improvement in floral and nesting resources, while other insect taxa benefitted from prolonged abandonment on heathlands. Honey bees were generally low in abundance on studied sites, even when placed in a species rich grassland. However, honey bees were highly abundant on heathlands during the late-summer flowering of Calluna vulgaris. Only few common species were detected on C. vulgaris and honey bees showed slight negative effect on oligolectic solitary bees and migratory butterflies.
The predominant threat to wild bees is loss of habitats and with nearly half of Danish bee species found across the studies, the thesis demonstrate the value of preserving and restoring semi-natural grasslands and heathlands as well as the consequences of abandonment. The presented studies do not indicate that managed honey bees constitute a significant threat to wild bees of semi-natural grasslands and heathlands, but it is strongly encouraged to consider the context-dependent potential of impact and assess resource-use of hives if placed near or within protected areas.

A digital version of the PhD thesis can be obtained from the PhD secretary