The Vegetation Composition And Succession Characteristics Of Alpine Meadow Under Different Utilization Intensities

From 2014 to 2016,we monitored the herbage height,coverage,number of species,biomass,and the soil and herbage nutrients of light,moderate and severe alpine meadows on the northeastern margin of the Qinghai-Tibet Plateau,and analysed the functional groups biomass composition,important values and niche breadth of species,Runkiaer frequency grading and succession composition type.This clarified the evolution rule and differential characteristics of three communities,determined the suitable grassland utilization intensity in the study areao.The main results were as follows:The number of species,herbage heights and coverages in heavy grazing grassland was lower than that in moderate and light grazing grasslands.The moderate grazing treatment reduced the number of hemicryptophytes and increased the number of geophytes.For light,moderate and severe grazing grasslands,the roots biomass in 0-10 cm depth soils distributed about 67.0% to 77.3%,59.5% to 75.5% and 55.3% to 82.0%,respectively.The aboveground and root biomass decreased with the grassland grazing intensity increased.The dominant species and functional group biomass composition oppcupied by Elymus nutans and Stipa sareptana in light grazing grassland,while it was Kobresia capillifolia and Elymus nutans in moderate grazing grassland and was Kobresia humilis in heavy grazing grassland.The number of poisonous species in heavy grazing grassland was higher than the others.The life form biomass composition dominated by hemicryptophytes in light grazing grassland and by hemicryptophytes and geophytes in moderate and heavy grazing grasslands.The hemicryptophytes and geophytes biomass composition in heavy grazing grassand was lower than that in moderate grazing grassland.The invader biomass composition was higher in heavy grazing grassand than that in light and moderate grazing grasslands.The Fe content in herbage was heavy grazing grassland >light grazing grassland,the herbage Mn contents was heavy grazing grassland >moderate grazing grassland.The soil trace elements in 0-10 cm was sensitive to grazing intensity during the period of seedling establishment,the Fe content in soil was light grazing grassland >heavy grazing grassland,the content of Mn and Zn were light grazing grassland =moderate grazing grassland>heavy grazing grassland.The soil N content,N/P and N/K were light grazing grassland = moderate grazing grassland>heavy grazing grassland.The community succession value was moderate grazing grassland>severe grazing grassland.The Runkiaer frequency coefficient distribution was a typical anti-J type in moderate grazing grassland and the communities was in a more stable and mature stage;while light and heavy grazing grasslands didn’t show a anti-J type and the community stability of the latter was in the succession stage.The result of this study supports the moderate disturbance hypothesis.