Assessing nutrient enrichment and grazing rest effects on grass establishment: implications for exotic and native species

Anthropogenic activities have altered resource availability and disturbance regimes, to reduce the richness of native plant species and favoring the invasion of exotic species in grasslands. Therefore, it is crucial to understand the factors that control the establishment and expansion of exotic plants, as well as the limitations for the reestablishment of native species. The objective of this study was to experimentally evaluate in the field whether grazing rest, fertilization, and interactions with established vegetation modulate the spontaneous recruitment of exotic and native grasses, and whether these factors modify the interactions between established vegetation and seedlings. This experiment had a split-plot factorial design with 5 replicates in randomized complete blocks. After two years of grazing exclusion with cages, nutrient addition, and continuous removal of exotic and native groups, the total number and dry weight of newly established seedlings were measured. Fertilization and grazing rest were found to modulate the establishment of both exotic and native grass seedlings, while no significant changes were observed in the competitive situation. The number of exotic grass seedlings increased by 79% with grazing rest and by 149% with nutrient addition, while the establishment of natives was halved with grazing rest. In conclusion, both grazing rest and fertilization significantly impacted the establishment of native and exotic grasses in a short period. The results of this study provide evidence of a key process, establishment, and could help design management plans for temperate grasslands to prevent the invasion of exotic forage grasses and maintain the recruitment of native grasses.