Influence of yak dung collection on characteristics and productivity of plant functional group of alpine meadow

In most pastoral areas of the Tibetan Plateau, yak dung is the only life energy source of herdsmen due to inconvenient traffic, energy shortage and life custom. Long term removal of large amount of yak dung from grassland ecosystem changes the amount and area of dung spots which induces nutrition recycle change of grazing grassland. The plant community and biomass of grassland consequently changes and ecological risk rises. To explore the ecological effects of yak dung collection, this paper focused on the characteristics and productivity of plant functional groups under full, half and none yak dung collection treatments in moderate grazing alpine meadow ecosystem in Henan County, Qinghai Province. Plant composition, important values of plant species, vegetation growth and community characteristics of alpine meadow under different dung collection treatments were investigated after three years experiment. The results showed that under yak dung none-collection treatment, grassland productivity was significantly lower than those under half-collection and full-collection treatments, while biodiversity was significantly lower than that under half-collection treatment. The biomass of high quality gramineae forage grass was significantly higher than those under half-collection and full-collection treatments, the biomass of high quality cyperaceae forage grass was significantly higher than that under full-collection treatment. Under yak dung half-collection treatment, biomass was 42.60 g.m^-2 with a significant increase of 9.7% compared with non-collection treatment. Vegetation abundance of yak dung half-collection treatment significantly enhanced 31.9%, while high quality forage grasses biomass unchanged compared with non-collection treatment. Under yak dung full-collection treatment, biomass and vegetation abundance significantly increased by 4.1% and 10.7%, respectively, high quality forage grass biomass decreased, meanwhile poisonous weeds biomass increased compared with non-collection treatment. Grass palatability of full-collection treatment got worse. Half or full collection of yok dung reduced the biomass of high quality forage grasses of gramineae and cyperaceae, especially cyperaceae grass biomass reduced by more than 70% under yak dung full-collected treatment. Leguminous grass biomass significantly increased by more than 5 times, while weeds and poisonous weeds biomass accounted for 74%79% total biomass. It was indicated that moderate collection of yak dung increased vegetation richness and diversity, insured grass palatability, and meantime provided energy resource for herdsman in alpine meadow. The results may provide a principle for yak dung collection and scientific management of moderate grazing alpine meadow ecosystem.