Diversity patterns of wild bees and wasps in managed boreal forests: Effects of spatial structure, local habitat and surrounding landscape

Understanding patterns of species diversity at different spatial scales is important for adapting management and conservation efforts. We have therefore studied wild bee and wasp (Hymenoptera: Aculeata) diversity structure in forest landscapes and evaluated the importance of conservation management at the local and landscape levels. Surveys were conducted at 32 clearcuts in eight landscapes in a managed boreal forest region. We assessed the influence of local habitat and landscape composition on species richness patterns and the effect of prescribed burning and landscape affinity on species composition for all bees and wasps as well as ecological and functional groups. The relative contribution of alpha and beta diversity on the regional level was assessed by diversity partitioning and the beta diversity between landscapes further partitioned into components of species turnover and nestedness. Bee and wasp species richness increased with high flower richness and clearcut size, and species composition differed between burned and unburned sites. Thus, flower-rich early-successional sites in boreal forest landscapes are important habitats for wild bees and wasps. To support this fauna, openness should be maintained for extended periods by delaying or avoiding tree plantation at flower-rich spots on clear-cuts. Beta diversity between landscapes accounted for the greatest proportion of the total regional gamma diversity, and over 70% of this diversity was due to species turnover. This implies that in order to maintain regional diversity, conservation efforts should be spatially dispersed, i.e. applied to every landscape of a few hundred square kilometers and adapted to the local species assemblages.