The potential role of “soft” management in sustaining wild bee populations in riparian marginal areas of Mediterranean regions

Increasing trophic resources by sowing flower strips, in arable lands or inter-row of permanent tree crops, is among the “landscapes and biodiversity” measures supported by the European CAPs to favour pollinating insects. To be effective and offer the proper trophic support to the diversity of pollinating insects, this action requires an accurate choice of the plant mixtures to be sown, in terms of flower shape and colour, and flowering times. Similarly, sowing entomophilous plants in marginal disturbed areas can enrich the pollinator community in urban and periurban contexts. In this study, we have sown different plots of recently reconfigured flood detention basins with three types of mixtures (two commercial and one non-commercial) of entomophilous plants in two lowland periurban zones in Tuscany (Italy). Sowing took place in 2022, and monitoring of vegetation and wild bees was carried out every two weeks from 2022 to 2024. We observed that the total abundance of bees increased significantly thanks to the presence of both sown and spontaneous flowering plants, the latter favoured by tillage. Our analyses showed that the bee species are expected to increase by 16.1 % for each additional flowering species. Therefore, we demonstrated that by combining suitable plant mixtures with one annual mowing, marginal areas along rivers in periurban contexts are indeed very appropriate to sustain an abundant and diverse bee community (about 17 % of Italian wild bee fauna), including species of conservation concern.