A 12-Year Experimental Design to Test the Recovery of Butterfly Biodiversity in an Urban Ecosystem: Lessons from the Parc Urbain des Papillons

SIMPLE SUMMARY: In a world where city dwellers are disconnected from nature, scientists are sounding the alarm regarding the decline in pollinators both in the countryside and in cities. Among these pollinating insects, butterflies are a particular focus of study, as their populations are declining sharply as a result of urbanization and the artificialization of vegetation. An ecological engineering project based on a plantation of host and nectariferous plants and backed up by a well thought out management approach was carried out in Marseille at the Parc Urbain des Papillons (the Butterflies Urban Park). We succeeded in almost doubling the number of butterfly species over the 12 years of the project. Mediterranean species that were rare at the beginning of the monitoring survey colonized the site. However, the monitoring of a nearby natural wasteland shows that some species are still absent. The plant palette used proved its effectiveness, and it would be worth duplicating this system in other urban contexts to encourage butterflies to remain in the city. ABSTRACT: Urbanization is one of the main threats to biodiversity. However, some urban green spaces could act as refuges for urban fauna if the composition of the flora were less horticultural and if a less intensive management strategy is adopted. Among the taxa, butterflies are experiencing a strong decline from European to regional scales. An ecological engineering project based on a plantation of host and nectariferous plants backed up by a well thought out management strategy was carried out in Marseille at the Parc Urbain des Papillons (the Butterflies Urban Park). We assessed its effectiveness by comparing the butterfly communities in this park before and after the engineering work, and we compared it to a neighboring wasteland with natural habitats. After 12 years of the project, the results show a significant change in the species composition. The species richness greatly increased from 25 to 42 species. Some specialist species we targeted appeared, and their numbers increased from one to five. However, three Mediterranean species are still absent compared to the wasteland with natural habitats. As the plant palette used and the management strategy implemented enabled us to significantly increase the number of species, we now plan to work on the structure of the vegetation.