Mechanisms for perennial grass dominance under small herbivore exclusion in an Inner Mongolian grassland

Herbivores significantly influence plant communities by modifying interspecies relationships, which in turn impacts ecosystem functioning. Although excluding herbivores is expected to enhance the dominance of perennial plants, few studies have consistently explored how plants adjust the growth-defense-reproduction trade-off in response to changes at different stages of herbivore exclusion. We conducted a controlled fence experiment in Inner Mongolia grassland to examine the effects of vole exclusion on the dominance and adaptation strategies of two perennial grasses. We found that twelve years of Brandt's vole grazing altered the plant community composition, but in the second year of the exclusion experiment, Leymus chinensis quickly regained its dominance. This rapid recovery was facilitated by L. chinensis strategically shifting its growth-defense-reproduction investment over time. In the early exclusion phase, L. chinensis quickly enhanced its competitive edge by prioritizing vegetative growth and clonal reproduction. As the exclusion period progressed, the species transitioned to seed-based dispersal to enhance population fitness. In contrast, the dominance of Cleistogenes squarrosa was largely influenced by interspecific interactions rather than intrinsic adaptive changes. These results reveal plants can dynamically adjust their resource investment strategies to optimize population fitness at different stages of vegetation recovery. This enhances our understanding of plant community dynamics and the establishment and maintenance of dominant species in grassland ecosystems.