Rewilding Europe's large grazer community: how functionally diverse are the diets of European bison, cattle, and horses?

Trophic rewilding is the introduction of species to restore top–down trophic interactions and associated trophic cascades to promote self‐regulating biodiverse ecosystems. A core example of trophic rewilding is the restoration of large mammalian grazer communities to restore or maintain biodiverse open to half‐open landscapes. Across Europe, cattle and horse breeds are being introduced as substitutes of the extinct aurochs ( Bos primigenius ) and tarpan ( Equus ferus ). More recently, European bison ( Bison bonasus ) is being introduced because it is supposed to fill a niche that pure grazers such as cattle and horses leave empty, especially in terms of reducing woody encroachment. But how functionally diverse are the diets of these three species? We investigated this question in the Kraansvlak pilot; a trophic rewilding project in the Netherlands where European bison, horses, and cattle have been introduced in spatially heterogeneous landscapes of forest, shrub land, and grassland. We present 4 years of data from direct observations on the diet use of all three species. Whereas cattle and bison included a significant proportion of woody plants in their diet throughout the year, horses strictly grazed. However, cattle and bison differed clearly in terms of the woody plant part they used (bark vs. twigs), and we discuss how this may affect the way they influence vegetation structure. Finally, we discuss the implications of our study for the increasing number of trophic rewilding initiatives in Europe.