Generalist flowers recover rapidly in grassland restoration: The importance of floral traits in community reassembly

Community assembly process, through biotic and abiotic filtering of species traits, is crucial for understanding the recovery of biodiversity and ecosystem function in restored ecosystems. While previous studies have highlighted very slow recovery of pollination networks in ecological restoration, the reassembly process of plant communities focusing on floral traits that influence pollination networks remains underexplored. We hypothesised that plant species with flowers that allow visits by various pollinators (generalist flowers) would recover more easily than those with flowers which limit pollinators (specialist flowers) during grassland restoration. We investigated floral trait assemblages, interaction patterns with pollinators, and pollination success for each floral trait (floral tube and colour) across 28 pollination networks. We examined their temporal change patterns within restored grasslands (2-75 years old) and compared them with reference old grasslands (>165 years old). Our results revealed that generalist (open/shallow and white/yellow) flowers have recovered rapidly, interacting with many pollinator species with similar traits in the early stages of restoration. In contrast, specialist (long-tubed and blue/purple) flowers exhibited more delayed recovery due to low pollination success, taking approximately 75 years for the recovery to the levels of reference old grasslands. Importantly, we found that functional specialisation was crucial for the recovery of these specialist flowers. Corresponding to temporal changes in floral trait assemblages, pollinator composition has shifted from dipteran dominance to a greater abundance of long-tongued bees, with interaction patterns of each trait group approaching those of old grasslands. Our findings underscore the pivotal role of floral trait reassembly in influencing temporal changes in pollinator community, network structure, and pollination function during grassland restoration. By integrating trait-based framework, this study provides novel insights into the co-reassembly process of plants and pollinators in restored ecosystems.