Grassland Restoration Drives Strong Multitrophic Biodiversity Recovery, but Climate Extremes Jeopardize Drought-Sensitive Species

Semi-natural grasslands, Europe's most biodiverse ecosystems, are rapidly declining due to agricultural intensification, abandonment, and afforestation, leading to biodiversity loss and reduced ecosystem function. Despite their ecological value, grasslands are often overlooked, while afforestation, for instance, is prioritized for climate mitigation. This study assessed the effects of grassland abandonment, afforestation, and ecological restoration on multitrophic species richness and soil conditions. We used Estonian semi-natural calcareous grasslands (alvars) as a model system. Results showed that historically overgrown and afforested grasslands recover fast and rapidly become species-rich after woody plant removal and low-intensity grazing reinstatement. These grasslands also serve as stable carbon sinks, storing soil carbon at levels comparable to afforested grassland areas, with restoration having no negative impact on carbon storage. Multitrophic species richness responded to restoration in three main ways: fast responders (plants, pollinators, birds) recovered relatively quickly, slow responders (lichens, bryophytes, soil fungi) showed little to no short-term change, and drought-sensitive species (ground-dwelling arthropods) declined due to prolonged drought, which also potentially overshadowed the impact of restoration. Grassland restoration is vital for biodiversity, the sustainable supply of ecosystem services, and climate resilience, with long-term monitoring needed to track recovery.