Body size of herbivores is a key reason underlying the interaction between herbivores and plant diversity, and the body size explains many of the phenomena connected to herbivore-plant interaction. Small herbivores are less likely to decrease plant diversity. Because small non-digging animals may not cause many disturbances to the plant and the environment. Intermediate-sized herbivores mostly increase plant diversity by consuming or influencing the dominant plant species, such as herbivore birds, that can directly use dominant plant species. While some herbivores enhance plant diversity by indirect effects on plant competition. Some digging animals at this size local community environmental fluctuations. And the adaptation of plant species to avoid predators can also adjust the vegetation structure and increase diversity. Larger herbivores often increase plant diversity. They use competitively dominant plant species, and disperse seeds and create disorder of the soil. Besides, their urine position also adjusts the local plant distribution, and prevent light competition.