Effects of plateau pika activities on seasonal plant biomass and soil properties in the alpine meadow ecosystems of the Tibetan Plateau

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.