Wild large herbivores promote plant diversity and functional redundancy by reducing dominance

Abstract Large herbivores can strongly shape plant communities, yet studies report contrasting effects on species richness, and how they affect plant functional diversity remains largely unknown. Moreover, despite important advances in the last years, our mechanistic understanding of herbivore effects on plant communities is still rudimentary. Here, we sampled plant species, vegetation structure and a suite of functional traits in and outside of six large, long‐term exclosure experiments (1.6–420 ha; 21–71 years) spanning savanna and thicket biomes in South Africa to quantify wild large herbivore impacts on plant diversity and vegetation structure and identify underlying mechanistic pathways. All sites were inhabited by (nearly) intact herbivore communities. Large herbivores increased total plant species richness and Shannon diversity by reducing dominance and promoting herbaceous species. This was linked to higher plant functional diversity and redundancy. Herbivore effects on diversity were strong in savanna but absent in the thicket. Furthermore, herbivores reduced vegetation height and density in both biomes, but this was unrelated to diversity changes. Plot‐ and site‐scale results were directionally consistent (though significance varied), suggesting that local responses may extend to broader scales. Our results indicate that large herbivores increase plant diversity and functional redundancy in the savanna biome by reducing plant dominance rather than via changes in vegetation structure. These findings suggest that ecosystems with intact herbivore communities may be more resilient and highlight the importance of protecting and restoring large herbivore populations. Read the free Plain Language Summary for this article on the Journal blog.