Highland cattle grazing reduces shrubland cover and increases plant diversity in green alder-encroached pastures

Alnus viridis is a shrub species encroaching mountain pastures in Central Europe, with negative economic and ecological consequences. Targeted grazing with robust livestock breeds may limit its spread and help to restore pastures, but its effectiveness on recovering plant diversity and forage quality remains unclear. This study was conducted on two summer pastures in the Alps encroached by A. viridis : Val Vogna in Italy, where Highland cattle were introduced in 2009, and Bovonne in Switzerland, where they were introduced in 2019. We characterised vegetation cover changes over the past decades using images analyses, evaluated animal movement patterns using GPS tracking, and conducted vegetation surveys to assess Highland cattle impact on plant diversity and pastoral value between 2019 and 2024. Shrubland cover decreased by 8 % at Val Vogna and 4 % at Bovonne after cattle introduction. Species richness increased from 25.5 to 32.2 at Bovonne and from 30.6 to 32.9 at Val Vogna, alongside an increase in the effective number of species. Pastoral value of open pastures at Bovonne improved from 12.9 to 17.7. Patterns of animal movement indicated a preference for pastures rather than shrublands; though at Bovonne they increasingly grazed within A. viridis stands over time. Differences between sites may partly reflect the longer grazing history and habits of Highland cattle at Val Vogna, where they were introduced a decade earlier. Overall, our study highlights the potential of Highland cattle as an effective tool to counteract A. viridis encroachment and restore the plant diversity of encroached pastures. • Highland cattle grazing reduces shrubland cover in encroached areas. • Plant diversity increases even 15 years after Highland cattle introduction. • Highland cattle grazing improves pasture forage quality after introduction. • Highland cattle gradually adapt to the habitat, entering encroached zones over time. • Highland cattle are an effective tool for restoring encroached mountain pastures.