Effectiveness of flowers strips on insect’s restoration in intensive grassland

Abstract

Intensification of grassland management causes a decrease in insect diversity. However, the mowing also causes substantial damage to insects if too homogeneously applied, especially for insect species with specialized needs. The overarching goal of the study was to investigate the restorative effect of flower strips on adjoining intensive grasslands to preserve and restore native grassland insect diversity. In 2020–2021, we analyzed how flower strips enhance Heteroptera, syrphids and butterflies diversity in adjoining intensive grassland compared to separated intensive (control) and extensive grasslands within the Austrian alpine range. Heteroptera and syrphid species richness and syrphid abundance were significantly higher in flower strips compared to other studied grasslands. However, butterfly abundance and species richness were significantly higher in extensive grasslands compared to flower strips. Heteroptera species assemblages in extensive grasslands were significantly different between flower strips, intensive and control grasslands. Further, Heteroptera abundance and species richness increased with an increase in flower cover and vegetation height. Similarly, syrphid abundance and species richness significantly increased with flower cover but decreased with vegetation structure. Butterfly abundance increased with plant species, however, species richness decreased with vegetation height. Altogether, 39.4% Heteroptera, 39.7% syrphid and 51.2% butterfly species were similar between flower strips and adjoining intensive grasslands. Restoring biodiversity in intensive grasslands represents a real conservation challenge. Flower strips seem most effective to enhance syrphid abundance that showed potential spill-over effect to intensive grasslands. Beside this, flower strips restorative effect is taxa specific. Overall, restoration of insect diversity is a relatively slow process, in which colonization by each insect group is not only limited by local vegetation conditions but is also affected by the presence, distance, and connection to source populations. However, maybe after more than two years intensive grassland is more promoted by adjoining flower strips. The results of the present study could be used to push for more active implementation of flower rich habitats as supplement areas as well as for the conservation of extensively managed grasslands. This will allow both, productive agricultural land use while maintaining and promoting insect habitats, and increase in species diversity within a heterogeneous landscape.