Post-restoration grassland management overrides the effects of restoration methods in propagule-rich landscapes

Grassland restoration is gaining momentum worldwide to tackle the loss of
biodiversity and associated ecosystem services. Restoration methods and
their effects on ecological community reassembly have been extensively
studied across various grassland types, while the importance of
post-restoration management has so far received less attention. Grassland
management is an important surrogate for natural disturbances, which most
ancient grasslands have co-evolved with. Thus, without the reintroduction
of management-related disturbance, restoration targets are unlikely to be
achieved in restored grasslands. In this study, we aimed to explore how 20
years of management by mowing once a year or light cattle grazing, affects
restoration success in Palearctic meadow-steppe grasslands restored by
either sowing native grasses (‘sown sites’), applying Medicago sativa as a
nurse plant (‘Medicago sites’), or allowing spontaneous succession
(‘spontaneous sites’). We found that following mowing, sown sites
maintained long-lasting establishment limitation, while Medicago sites
seemed to have experienced a delay in succession. These limitations
resulted in low total and target species richness, low functional
redundancy and distinct species and functional composition compared to
reference data from ancient grasslands. Spontaneous sites that were mowed
reached a more advanced successional stage, although they did not reach
reference levels regarding most vegetation descriptors. Sown and Medicago
sites that were grazed had higher total and target species richness than
those that were mowed, and showed restoration success similar to that of
spontaneous sites, on which grazing had only moderate further positive
effects. Grazed sites, irrespective of the restoration method, were
uniformly species rich, functionally diverse and functionally redundant,
and thus became important biodiverse habitats with considerable
resilience. We conclude that an optimally chosen post-restoration
management may have an impact on long-term community reassembly comparable
to the choice of restoration method. Restoration planners may, therefore,
need to put more emphasis on future management than on the initial
restoration method. However, our findings also imply that if local
constraints, such as potentially high invasive propagule pressure,
necessitate the application of restoration methods that could also hinder
the establishment of target species, the long-term recovery of the
grassland can still be ensured by wisely chosen post-restoration
management.