A Study On Grazing Degenerate Succession Of Alpine Meadow In North-west Of Sichuan

Kobresia setchwaneusis community of alpine meadow in north-west of Sichuan was used as material to study community characteristics of Kobresia setchwaneusis and soil on meadow nutrients variety under the four grazing intensity of nothing, light, middle and heavy, diversity of community, quantitative structure of community and rules of soil nutrients variety were analyzed, succession stage of community grazing was divided preliminarily, monitoring indexes of sensitive to grazing degeneration were selected by principal components analysis (PCA),the results showed:1 Diversity of community decreased with the increase of grazing intensity, but diversity of light grazing plot was higher than that of controlled plot, the sequence of diversity indexes of all plots was light grazing>controlled>middle grazing>heavy grazing. Variation trend of community richness and uniformity was consistent with that of community diversity, maximum of all plots' richness and uniformity also appeared in the light grazing plot. Effect of grazing interference on community uniformity was not big, there was only trifling fluctuation among controlled, light and middle grazing plot, but community uniformity of heavy grazing decreased rapidly.2 Above-ground biomass of alpine meadow decreased gradually with the increase of grazing intensity, the difference between all plots reached obvious level(p<0.05),which showed overgrazing directly lead to the decrease of meadow productivity.3 Dominance of alpine meadow plant species changed obviously under different grazing intensity, dominance of excellent forage(Kobresia setchwaneusis, Kobresia pygmaea) decreased gradually, dominance of other grasses (Potentilla anserina, Plantago asiaticd) and poisonous plant(Anemone rivucaris, A.trullifolia var. linerrid) increased gradually, structure of plant community changed obviously.4 The analysis of plant community dominance under different grazing intensity may determine succession series of alpine meadow under grazing interference ,it was Kobresia setch\vaneusis+ Kobresia Pygmaea+ perennial forbs+ Perennial grass community-Kobresia pygmaea+Kobresia setchwaneusis+perennial other grasses community "perennial other grasses community -Potentilla anserina + Ranunculus brotherusii-bier\nia\ other grasses community. The four community types were determined degeneration of nothing, ligltt, middle and heavy community associating with other community characteristics. The total trend of succession was from tall erect -growth kobresia community to short prostrate-growtii forbs community, the vertical perennial forbs community was transition.5 Grazing interference gave certain effect on soil of alpine meadow. The content of soil organic matter decreased obviously with the increase of grazing intensity, especially superficial soil changed obviously. The change degrees of the content of available N increased with the increase of grazing intensity. The content of total N,P,K, available P,K and pH was smaller from controlled plot to middle grazing plot, but there was an obvious leap in heavy grazing plot.6 Aboveground biomass was sensitive index of monitoring alpine* meadow degeneration. Potentilla anserina, Ranunculus brotherusii, Plantago asiatica may be used as auxiliaiy indexes of monitoring heavy degeneration meadow. Anemone rivucaris and A. nemonetruldelium var. linerria may be used indexes of monitoring middle degeneration meadow. The content of soil organic matter and available N were soil indexes of moee sensitive to monitoring meadow degeneration.