Semi-Feral Horse Grazing Benefits the Grassland Diversity of Flowering Plants Including a Pollinator-Promoting Indicator Species

European grasslands and their biodiversity are declining rapidly due to land use changes, which highlight the need to develop effective restoration strategies. This study investigates the impact of reintroducing the Swedish national horse breed (the Gotland Russ) on grassland plant diversity and evenness in abandoned agricultural landscapes in Southeast Sweden. Twelve horses were introduced into three 10-13-hectare enclosure replicates (four horses per enclosure) in a three-year (2014-2016) rewilding experiment. Plant species richness, evenness, and diversity were investigated in both grazed and un-grazed conditions. The results indicate that horse grazing significantly increased grassland plant species diversity and richness, with higher Shannon and Simpson's diversity indices in grazed areas. In addition, the abundance of white clover (Trifolium repens), a signal species beneficial to pollinators, increased significantly in grazed areas. These findings emphasize the need for integrating large herbivore grazing into ecological restoration practices. Considering the recently enacted EU Nature Restoration Law, which aims to restore 20% of Europe's degraded ecosystems by 2030, this research provides critical insights into scalable restoration methods. The implementation of restoration strategies that include large herbivores may enhance the resilience and biodiversity of European grasslands, thereby aligning with the EU's restoration goals.