The foraging and burrowing activities of small mammalian herbivores may have either detrimental or beneficial effects on grassland ecosystems; the direction of the effect is determined by the species, population abundances and fluctuations. Twelve survey sites with active burrow of plateau pika were classified into four degrees of density: approximately zero-density, low-density, medium-density and high-density, to evaluate the impact of different pika densities on vegetation, plant biomass, soil organic carbon and nutrients in a whole growing season. We show that pika as a main supplement to livestock activities contributed to a decrease in the number of plant species, vegetation cover, plant height and seasonal mean biomass, while values at medium-density site except above-ground biomass were the lowest. With the exception of available potassium, soil organic carbon, nitrogen, total phosphorus and soil water content, zero-density areas were significantly higher than those of pika occupied areas. However, there were slight or no differences in vegetation characteristics and soil properties between medium-and high-density sites. Our study suggests pika activities with high-density made palatable forage less and soil carbon and nitrogen more than low-density, moreover, plateau pika had greater impacts on above-ground vegetation than on root system.
