How long does it take for bees to return to restored grasslands?

The importance of preserving old grasslands as reservoirs of biodiversity, even if it is just as ski slopes, has become clear. Recovered grasslands need more than 75 years of continuous management to regain their biodiversity because specialised pollinators are slow to return. It takes 75 years of continuous management for the plant diversity in recovered grasslands to finally reach levels comparable to ancient grasslands. However, that’s still not enough for the pollinator community. Even after 75 years, pollinators are still less specialised and less successful at pollinating the plants, although the community continuously shifts towards higher specialisation and successful pollination as grasslands get older. What drives this lag is not a lower diversity of pollinators in itself, it is the identity of the pollinators. Recently restored grasslands are visited mostly by flies and hoverflies that are generalists and thus often carry pollen from one plant to flowers of a different species. On old grasslands, on the other hand, pollinators are to a larger extent bees and butterflies that specialise in one species at a time, thus guaranteeing that the pollen is transferred to the right plant species. The study therefore shows the importance of considering pollinator communities for efforts targeting the conservation of threatened grassland plants. First of all, this means that maintaining ancient grasslands as reserves for specialised pollinators should be a top priority for conservationists.