Grazing reduces plant sexual reproduction but increases asexual reproduction: A global meta-analysis

Grazing affects grasslands worldwide. However, the global patterns and general mechanisms of how grazing affects plant reproductive traits are poorly understood, especially in the context of different climates and grazing duration. We conducted a meta-analysis of 114 independent grazing studies worldwide that measured plant reproductive traits in grasslands. The results showed that the number of tillers of plant increased under grazing. Grazing did not affect the number of reproductive branches of forbs, but significantly reduced the number of reproductive branches of grasses. Grazing increased the number of vegetative branches of all plants and reduced the proportion of reproductive branches. Grazing significantly reduced the number of flowers in forbs. Seed yield in the two plant functional groups was reduced compared with no-grazing. Under grazing, the sexual reproduction of grasses decreased much more substantially than that of forbs. This may be due to biomass allocation pattern of grasses under grazing (i.e., belowground versus aboveground). Under grazing, plants tended to adopt rapid, low-input asexual reproduction rather than long-term, high-risk sexual reproduction. This study represents the first large-scale evaluation of plant reproductive trait responses under grazing and demonstrates that grazing inhibits sexual reproduction and promotes asexual reproduction. The effect of grazing on plant sexual reproduction was influenced by grazing intensity, mean annual precipitation, and grazing duration. These results will assist in the development of sustainable grazing management strategies to improve the balance between human welfare and grassland ecosystem health. Conceptual diagram of grazing effects on plant reproduction. Grazing significantly reduces the aboveground biomass (AGB) of plants and the nutrient content in the soil, prompting plants to allocate greater resources to belowground biomass (BGB), resulting in an increase in belowground biomass and tiller number. Forbs reduced the allocation to sexual reproduction by increasing the number of vegetative branches. Grasses reduced the allocation to sexual reproduction by increasing the number of vegetative branches and reducing the number of reproductive branches. The interference of grazing shortens the overall phenology of the plant, reducing sexual reproduction output. The decrease in plant-pollinator network diversity in forbs is also a main reason for the decrease in sexual reproduction suc