Fewer butterflies and a different composition of bees, wasps and hoverflies on recently burned compared to unburned clear-cuts, regardless of burn severity

Insect pollinators are declining, which often is related to intensified agriculture. Less focus has been on the effect of forestry. In many boreal forests, clear-cutting has replaced fire as the main disturbance agent, which has been negative for many species. Therefore, prescribed burning is performed, often on clear-cuts. Knowledge on the effect of fire on pollinators is, however, scarce. We sampled pollinators and their resources in 22 burned and 15 unburned clear-cuts in and around a large wildfire area in Sweden, three years after fire. We compared potential pollinator resources as well as richness, abundance and community composition of four groups of pollinators: bees (totaling 583 individuals), wasps (1226), hoverflies (416), and butterflies (7 2 8) between burned and unburned clear-cuts. Moreover, we analyzed the effect of burn severity (depth of remaining humus). We show that the diversity and cover of potential nectar/pollen plants were clearly lower in burned clear-cuts, while potential nesting resources were higher. Butterfly richness was 67% lower and abundance 89% lower in burned clear-cuts. Differences in richness and abundance were smaller for bees, wasps, and hoverflies, but their species composition differed. We found no effect of burn severity on pollinators or their resources. We conclude that burned clear-cuts have fewer pollinators three years after fire, which is driven by a loss of butterflies. However, changes in species composition from clear-cut fires could complement the fauna of unburned sites when mixed at landscape level. Future studies should follow vegetation and pollinator communities over longer time periods following clear-cut burning.