Evaluation and Dynamic Analysis of Forage Value of Main Grassland Types in the Middle Section of Tianshan Mountains

【Objective】 Tianshan is an important mountain pasture in Xinjiang. In order to liberate the dynamics of grassland community quality under grazing conditions. 【Method】 the continuous positioning method was used to analyze the forage value dynamics of plant communities from 1985 to 2001. 【Result】 The research results showed that：（1） the good forage was the main composition in the desert steppe which can account for 80.1% of the average aboveground biomass over the years ; and the excellent and good forage can account for 59.5% of the aboveground biomass in grassland ; the value of the meadow grass communitye was low, and the medium and low forage grasses can account for 91.6% of the average over the years. （2） the aboveground biomass had a state of fluctuation in different grassland types, and different grassland types have different rules.it had lower annual variability in high forage value and lower annual variability in the community. 【Conclusion】 （1） The forage value of the grassland community is unstable, and it is greatly affected by the fluctuation of the biomass on the various pasture grasslands of the community. （2） The three types of grassland forages have different types of growth and decline patterns, which are always in continuous fluctuations between each year, and the fluctuation coefficient and annual variability between the years are large. （3） The fluctuations of the mountain desert grassland and mountain grassland are reversible, while the mountain grassland The changes in the feeding value of the main groups of the meadows cannot be completely restored to the original state, but only approaching the equilibrium state, which is a manifestation of the degradation of the community's feeding value due to over-utilization.