Study On Degradation Progress And Restoration Mechanism Of Plant Community In Qinghai Tibetan Plateau

Rapid land degradation and desertification have taken place in grassland and meadow of many sites in the world, by overgrazing due to very high stocking rates to sustain development of production and economy of human. And as well known stock farmers are keen to maintain high stock rates to reach topmost production;as a result, there is degradation and desertification in some places of Alpine meadow ecosystem in China. Hence it is key problem that understand the degradation progress and restoration mechanism of an ecosystem. Therefore, the study of degradation and restoration on grassland or meadow is one of the hot issues in ecology. The aim of this study was to detect degradation progress and restoration mechanism in Alpine meadow ecosystem of east Qinghai Tibetan plateau through simulated grazing at different soils fertility. Most studies have suggested that restoration success could be based on vegetation characteristics, species diversity or ecosystem processes, especially, the ecological consequence of biodiversity loss and effect of functional groups have aroused considerable interest and controversy during recently years. Ecosystem processes (productivity and nutrient recycling) result directly from the diversity of functional traits in the biotic communities, which is in turn determined by the species composition and diversity.As a result, species diversity was higher at the control plots and decreased significantly after five years of nutrient addition, and the trend of declining increased with fertilization levels increasing. Although the total species density was significantly decreased after nutrient addition, the graminoids density and aboveground biomass were significantly increased with nutrient increasing due to limited nitrogen for graminoids wascompensated after limited resources addition, especially in the highest nutrient addition plots. Productivity increased significantly with fertilization adding to the community, but the trend of increasing significantly drop with time continuing, that is continued fertilization can not maintain high productivity. However, intermediate clipping increased functional diversity at higher fertility in soils where only few functional groups survive. The compensation that was observed resulted from plants biomass subsequent to simulated grazing in the highest fertility plots. Over-compensation was detected only when lightly simulated grazing at intermediated fertility. The compensation and over-compensation merely happened on graminoids. We found that graminoids would be dominant when total aboveground biomasses exceed 50g/0. 25m2, sedges in the region on 25-50g/0. 25m2, forbs, unpalatable species and legumina were range in 0-25 g/0. 25m2. This distribution pattern benefit to predicting changes of plant community structure and composition. The changes of basic soil resources were analyzed after fertilization, the available nitrogen and organic matter have not significantly varied, but the available phosphorus increased significantly with soil fertility increasing. We deduced that limited element should be nitrogen rather than phosphorus in the alpine meadow. The plant community structure would change greatly once the concentration of nitrogen changed. Especially, species richness declined to 8 /0.25m2 from 30 /0.25m2 at the highest fertilization level within five years. The results from this study indicated that it is unscientific only depended on fertilization to establish a better management for degradation of the alpine meadow. We are not able to die out the unpalatable species because of its balanced role in ecosystem. It may not even be desirable to eliminate the weedy species. The differential responses of functional groups to simulated grazing are not only due, in part, to differences in growth capacity of the functional groups, but also available resource in soils and intensity of disturbance. The mechanism can shed lighton how plant communities are affected by grazing, and are useful for management of alpine meadow.Hypothesis of disturbance generally considered that species richness should be greatest at intermediate level of disturbance since dominance is prevented and the pool of potential colonists is relative large. We predicted effects of clipping mechanism as a disturbance on species diversity and aboveground biomass based on the hypothesis of disturbance. As a result, effects of short term different clipping regimes on species diversity and aboveground biomass depended on different fertility in soils on the alpine meadow. So the hypothesis based on some conditions, such as soils fertility, factors of climate and so on. Individual density play an important role at unimodal patterns between productivity and diversity, while, the relation between productivity and species richness changed with annals time changing. Although simulated grazing was not affect significantly some ecological factors during short time, such as species richness, aboveground biomass, and so on, it changed significantly relationships between productivity and diversity, productivity and individual density, diversity and individual density. In summary, we know the mechanism of disturbance, it plays an important role to understand the degradation and restoration for alpine meadow ecosystem, and furthermore, there is a theory for good management to development of the ecosystem.