Study On Quantitative Characters Of Plant Communities And Classified Index System Of Grazing Alpine Meadow In North-west Sichuan

The grazing degraded alpine meadow in North-west Sichuan, was used as material to study quantitative characters of alpine meadow plant community under the four grazing intensity of zero-grazing, light-grazing, middle-grazing and heavy-grazing. The variational rules of quantitative characters of the alpine meadow plant community under the four grazing intensity were concluded by analyzing the color, floristic composition, diversity and above-ground biomass. On this basis, the system of degradation classified index system of the grazing degraded alpine meadow in Ruo-er-gai altiplano, north-west Sichuan, was drafted combining with the characters of vegetation, soil and meadow productivity indexes etc. The results showed:1. The gramineous, sedgy and composite plant was dominant in the zero-grazing alpine meadow, which accounted for 34.8% in all plant species. In light-grazing, middle-grazing and heavy-grazing, the ratio of species number of above plant to the plant community decreased to 23.5%, 19.8% and 15.6% because of the grazing influence.The height of plant community decreased from the mean height 47.5cm to 36.2cm, 26.8cm and 13.6cm respectively. The color of plant community had more seasonal variance, but the color of plant community became simple by the floristic composition becoming single under the heavy grazing.2. The a-diversity of alpine meadow plant community measured by Shannon-Wiener index and Simpson index, the richness and uniformity, measured by Margalef index Pielou index shows the same variational rules. They all became higher at beginning and lowerlater varied identically with the increase of grazing intensity. The similarity coefficients of community species between adjacent grazing gradients were all not high, which proved the floristic composition of alpine meadow community under different grazing intensity has greater difference.3. The above-ground biomass of grazing meadow decreased with the increase of grazing intensity. The variances of above-ground biomass at different grazing intensity were significant (P<0.05) . The above-ground biomass of alpine meadow with different terrain had difference at the same grazing intensity. There were rules of flat>nothren slope>southern slope under the zero-grazing intensity. The difference at other grazing intensity was not significant.4.The stocking capacity at the four grazing intensity of zero-grazing, light-grazing, middle-grazing and heavy-gra^::g, were approximately 7.95, 4.35, 2.62, 0.89 yak-unit.5. The above-ground biomass of gramineous, sedgy and composite plant of several economic-community decreased with the increase of grazing intensity. The above-ground biomass of forbs, including poisonous grass, increase with the increase of grazing intensity. The above-ground biomass of leguminous and Polygonaceae plant varied inconspicuously under different grazing intensity. The variational rules indicated decrease of meadow quality led by grazing.6. On the basis of results prior researches, the qualitative and quantitative indexes, including the representative trait such as floristic composition of alpine meadow plant community, the characters of meadow vegetation, the content of soil organic matter, the above-ground biomass and productivity of alpine meadow, combining with data shown in this study, have been selected. The classified index system of the grazing-degraded alpine meadow in north-west Sichuan was drafted.