Flying insect biomass is negatively associated with urban cover in surrounding landscapes

Aim In this study, we assessed the importance of local to landscape-scale
effects of land cover and land use on flying insect biomass. Our main
prediction was that insect biomass would be lower within more intensely
used land, especially in urban areas and farmland. Location Denmark and
parts of Germany. Methods We used rooftop-mounted car nets in a citizen
science project (‘InsectMobile’) to allow for large-scale geographic
sampling of flying insects. Citizen scientists sampled insects along 278
five km routes in urban, farmland and semi-natural (grassland, wetland and
forest) landscapes in the summer of 2018. The bulk insect samples were
dried overnight to obtain the sample dry weight/biomass. We extracted
proportional land use variables in buffers between 50 and 1000 m along the
routes and compiled them into land cover categories to examine the effect
of each land cover, and specific land use types, on insect biomass.
Results We found a negative association between urban cover and insect
biomass at a landscape-scale (1000 m buffer) in both countries. In
Denmark, we also found positive effects of all semi-natural land cover
types, i.e. protected grassland (largest at the landscape-scale, 1000 m)
and forests (largest at intermediate scales, 250 m). Protected grassland
cover had a more positive effect on insect biomass than forest cover. The
positive association between insect biomass and farmland was not clearly
modified by any variable associated with farmland use intensity. The
negative association between insect biomass and urban land cover appeared
to be lessened by increased urban green space. Main conclusions Our
results show that land cover has an impact on flying insect biomass with
the magnitude of this effect varying across spatial scales. However, the
vast expanse of grey space in urbanised areas has a direct negative impact
on flying insect biomass across all spatial scales examined.