Local landscape elements enhance flying insect biomass in a complex agricultural landscape

A current response to counteract insect biomass decline is to create landscape elements like hedgerows and flower strips to agricultural landscapes to provide habitat for insects. However, little is known about the additive effects of such landscape elements on biomass of flying insects, especially in a landscape that has already been partly restored. Our study area has a relatively high landscape complexity due to past conservation efforts. Here, we determined the impact of hedgerows and flower strips on flying insect biomass using 3 years of Malaise trap data from 24 field edges with either a hedgerow, flower strip or field boundaries without such landscape element present. To accurately compare biomass of the collected samples, we used a Bayesian model with hourly biomass as a latent variable, including temperature anomaly and Julian day to correct for the influences of weather and seasonal patterns on insect biomass. This model was expanded with information on local vegetation and land management, proportionalized land use, total length of hedgerows, and edge density to assess the wider impacts of landscape complexity and configuration on insect biomass. Hedgerows had a significantly positive effect on mean hourly biomass: 0.231 g/h compared to the control locations (0.105 g/h), whereas flower strips had an intermediate estimate (0.150 g/h). As one of the few additional landscape parameters having an effect, the percentage of protected natural area in the surroundings contributed significantly to insect biomass. Our results show that local natural elements, particularly hedgerows, can add to insect recovery even in highly complex landscapes. The exact land use and landscape configuration in its vicinity contribute little, except for protected natural areas dispersed in the landscape.