Effects of grazing of livestock on grassland

The effects of grazing on herbage growth, population, community, soil and ecosystem were analyzed on the mechanisms and approaches in this paper. Grazing changed the allocation of mass and energy in aboveground and underground parts of herbage. The effects of grazing on the herbage growth depended on the grazing system, grazing animal, grazing intensity, grazing season, grazing cycle and vegetation component. Grazing also resulted in the compensatory growth of herbage by changing external factors and internal factors including improvement of canopy microclimate and soil properties, increase in photosynthetic ability and a decrease in respiration rate. Grazing livestock changes the interspecies competition through the direct action of ingestion and indirect action such as the change of soil properties. The regeneration of herbage was impacted by the ingestion, excrement and trampling of livestock. The factors affecting the structures and function of the herbage community consisted of biotic components, abiotic components and social components, of which active mechanism were discussed. The state-and-transition hypothesis of community succession gave a satisfactory explanation for the change in grazing land, while shrub invasion could not account for the degradation resulting from only grazing. Grazing intensity, grazing period and topography altered the response of soil to grazing, in which the direct actions included intake, trampling and excrement, and indirect action factors included the population structure, community structure, fertile island effect and topography. The response mechanisms of soil carbon to grazing were analyzed for soil respiration, litter C production and microbial biomass C. The mechanisms of temporal coupling, spatial coupling and interspecific coupling between herbage and livestock were discussed in order to improve productivity and health level of the grazing ecosystem. The effects of grazing on cycle of carbon, nitrogen and other elements and their response to global change were analyzed. According to development of international scientific research and requirement of pasture-livestock production in China, we suggest that animal selection in grazing management, release of the productive potential by compensatory growth, improvement of the scientific contents of feeding animals according to herbage and grazing intensity, fertilization management of grazing land, countermeasures of grazing management based on the global change and the health management of grazing ecosystem should be involved in the further study on grazing management.