Lawn management promoting tall herbs, flowering species and urban park attributes enhance insect biodiversity in urban green areas

Urban expansion transforms the availability and structure of habitats, shaping urban natural elements. This triggered a worldwide effort to reduce urbanization impact on biodiversity, mostly with biodiversity-friendly and less formal management in urban green areas. In this context, we evaluated the effect of lawn management promoting tall herbs on insects in urban parks. Moreover, we also tested the interplay of mowing regimes and green-area attributes, such as park size and tree distribution, by recording the insect species richness and the total and proportional abundances of several groups (i.e., honeybees, wild bees, wasps, hoverflies, non-syrphid flies, beetles, true bugs, grasshoppers, lepidopterans). The results from the first experimental year demonstrate that unmown sections increase insect abundance and species richness, while the regrowth after the first mowing of tall herbs was only moderately beneficial, compared to frequenlty mowed areas. Positive contributions by flower richness on the insect richness and by the aggregated tree distributions on insect abundance and richness were recorded. Negative relationships occurred between increasing graminoid cover and insect abundances and between park size and insect richness. Furthermore, most insect groups were promoted by plant height (except honeybees and flies) and they correlated with specific dominant plants in many cases. Overall, this study demonstrates the positive roles of tall herbs in urban parks, clarifying the influence of park attributes and lawn features, pointing out that a less intensive management regime with informal green areas could effectively enhance urban insect biodiversity.