Grassland plant diversity and ecosystem condition assessment in the hen harrier programme, Ireland, a results-based agri-environment scheme

Background High Nature Value farmland (HNVf) supports biodiverse, semi-natural habitats through extensive farming but is increasingly threatened in Ireland by land intensification and abandonment. Results-based payment schemes (RBPS) aim to maintain and enhance these habitats, yet their broader biodoversity benefits remain unclear.Aims This study examined the relationship between an RBPS scoring system developed for the protected hen harrier (Circus cyaneus) and semi-natural grassland plant communities.Methods Thirty grassland fields spanning a gradient of RBPS ecological condition scores from (0-10) were surveyed. Vegetation surveys were carried out in three 2 m × 2 m quadrats per fieldalong a ‘W’ transect walk, supplemented with additional environmental data as proxies for environmental conditions and management pressure. Non-metric Multidimensional Scaling was used to analyse species composition, and fields were assigned to a vegetation type using the Irish Vegetation Classification ERICA tool.Results Higher RBPS scores were positively associated with greater number and cover of positive indicator species, increased bryophyte cover, and higher floristic diversity indices. Lower scoring fields were associated with greater cover of negative indicator species, increased rush cover and higher Ellenberg’s Nitrogen and Reaction values. Eight wet grassland community types were identified.Conclusions Our findings indicate that an RBPS designed to incentivise ecological conditions for a target raptor species can also reflect wider plant diversity, supporting multiple ecosystem services in HNVf systems.