Effects of landscape composition on hoverflies (Diptera: Syrphidae) in mass-flowering crop fields within forest-dominated landscapes

Abstract

Agricultural intensifcation has led to structurally simplifed landscapes with reduced and fragmented resources for farmland insects. However, studies on the efects of landscape composition on farmland insects have mainly been performed in areas dominated by open arable land and semi-natural grasslands, while studies from forest-dominated landscapes are scarce. This research examined the efects of landscape composition on hoverfy species richness and abundance in arable land in boreal forest-dominated landscapes. Hoverfies were sampled in 22 mass-fowering caraway (Carum carvi) felds in Central Finland using pan traps. The efects of landscape composition on species richness and abundance were examined for all hoverfies, and for species groups with diferent adult habitat preferences. Landscape composition was measured as proportions of land cover classes within two diferent radii. Species richness and abundances of all hoverfies, forest species and open-habitat species increased with decreasing arable land cover and/or increasing forest cover within a 500 m radius (the two land cover classes strongly negatively correlated). Wetland species were most abundant in landscapes with an intermediate cover of arable land and forest, and most species-rich in landscapes with intermediate (10%) water cover. The species richness and abundance of mixed-habitat species increased with increasing cover of transitional woodland.