Effect Of Grazing Intensity On Characteristics Of Vegetation Communities In The Alpine Meadow Steppe

The experiment was conducted in an alpine meadow in Gongbujiangda of the TibetAutonomous District, the summer and winter grazing grassland in Huangyuan, Qinghai,respectively. Combining the survey methods of Binary occurrence number with abovegroundbiomass, we analyzed vegetation data using the gamma distribution model, the power law andthe beta-binomial distribution model. We aimed to examine quantitatively the effect ofgrazing intensity on community characteristics, such as vegetation composition, speciesdiversity, biomass and their spatial distributions from the point of view of spatialheterogeneity. We hope the study can provide a scientific basis for how to recover the speciesdiversity and to increase the productivity of degraded grasslands. Further more, through thisstudy, we hope we could come up with effective countermeasures for the maintenance ofspecies diversity and the protection of meadow ecosystems.The main conclusions obtained are as follows:(1) The spatial distribution of vegetation community on alpine meadow steppe fit thebeta-binomial distribution model, the power law, and gamma distribution model very well.Thus, this approach can be used in the quantitative study of grassland spatial heterogeneity.(2) Based on our research of above-biomass in the Alpine Kobresia Meadow underdifferent grazing intensities, we can concluded that the total number of species, speciesdiversity, the average number of species, the indexes of species diversity and biomass withinthe L-quadrats in the non-grazing grassland were higher than those for the medium grassland,and those for the medium grassland were higher than those for the heavy grazing grassland.Spatial heterogeneity for the entire community in the non-grazing grassland were higher thanthose for the heavy grassland, and those for the heavy grassland were higher than those for themedium grazing grassland. Therefore, the average biomass and species heterogeneity for theentire community were correlated negatively with the increase of grazing intensity. While thenumber of species and the occurrences of species showed significant negative correlation withbiomass. Moreover, Grassland vegetation species composition greatly changed. The numberof palatable forage grasses like Stipa capillata were greatly reduced. Instead, toxic weedsrepresented by Pedicularis kansuensis began to large area intrusion. This phenomenon showed the alpine meadow ecosystem had seriously degraded. However, the total number ofspecies, species diversity and the aboveground biomass were the highest and it indicated thatfencing enclosure was one of the most effective measures for the improvement of deterioratedmeadow.(3) Entire vegetation community in the Alpine Kobresia Meadow exhibited a stronglyheterogeneous distribution of vegetation (versus a random distribution). The index values ofspatial heterogeneity in the non-grazing grassland were higher than those for the grazinggrassland, and those for the heavy grazing plots were higher than those for the mediumgrazing plots. There were three common dominant species including Kobresia pygmaea,Stipa capillata, Primula tibetica under three different grazing intensities. Their index valuesof spatial heterogeneity in the medium grazing grassland were very low (δi=0), while therewas only index values of spatial heterogeneity of Kobresia pygmaea being low in thenon-grazing grassland and heavy grazing grassland. Therefore, the spatial heterogeneity in themedium grazing grassland was the lowest. The species diversity, evenness, abovegroundbiomass, the average number of species and species diversity within the L-quadrats for thevegetation community in the non-grazing grassland were higher than those for the mediumgrassland, and those for the medium grassland were higher than those for the heavy grazinggrassland.(4) The total number of species, the average number of species within the L-quadrats,the index values of species diversity and spatial heterogeneity for the entire community in thewinter grazing grassland was significantly higher than summer grazing land in Huangyuan,Qinghai. In the winter grazing grassland, Poa pratensis, Elymus nutans, Kobresia pygmaeaand other high-quality forage species increased due to fence protecting. While in the summergrazing grassland degradation species like Potentilla anserina and Plantago asiatica, becomedominant species and species diversity decreased. Overall, the spatial heterogeneity of wintergrazing grassland was higher than summer grazing pasture. Therefore, grazing in the winter isbetter than summer grazing so as to avoiding grass growing season in the production practice.