Does flowering synchrony contribute to the sustainment of dry grassland biodiversity?

• An index to measure temporal co-occurrence of flowering is proposed (“CF-index”).
• Entomophilous species have a non-random flowering pattern in dry grasslands.
• Mutualistic interactions shape the community flowering pattern.
• Flowering pattern is a key characteristic in shaping dry grassland species richness.
• Mutualistic interactions are related to dry grasslands conservation and restoration.

Phenological relationships among entomophilous species for pollination may play an important role in structuring natural plant communities.The main aim of this work was to test whether in dry grassland communities there is a non-random flowering pattern and if the pattern influences the species richness, and the richness of subordinate and common species.Field sampling was carried out in temperate dry grasslands in NE Italy. Species composition and the flowering phenology were monitored in 45 2 m × 2 m plots randomly placed over dry grasslands.To quantify the degree to which insect-pollinated species overlap in their flowering time we developed a “co-flowering index” (CF-index). The significance of the observed flowering pattern was tested using a null model.A positive correlation was found between the synchronic flowering and the number of subordinate species. Subordinate species showed shorter flowering length than the common species and a mostly specialized pollination system.Our findings suggest that flowering synchrony might be a key characteristic which may contribute to shape dry grassland composition by favouring the long lasting maintenance of rare species populations within the community.The comprehension of such functional relationships between species of different trophic levels is of great importance for the conservation of dry grasslands and the maintenance of the ecosystem services that pollination provides.