Abstract: The study on the dominance, niche breadth and niche overlap of twenty main plant populations on a warm-seasonal pastureland of alpine Kobrecia parvameadow under four grazing intensities showed that after two years grazing,K. parva and Elymus natans were the dominated plants in the control, light grazing, and moderate grazing plots, while Potentilla anserine and Pedicularis alaschanica dominated in heavy grazing plot. Because of their high endurancein grazing, drought, and tramping, K. parva, K. humilis and K. capillifolia had awide niche breadth, with the values being 0.938, 0.824 and 0.815, respectively. The niche breadth of E. natans was relatively narrow (0.805) owing to its bad biological characters in enduring grazing, drought and tramping. The niche breadths of D. kokonorica, Stipa aliena, S. purpurea, Festuca rubra and Ptilagrostis dichotoma based on grazing gradients were all very narrow, with the values being 0.226, 0.448, 0.445, 0.608 and 0.605, respectively, indicating that grazing restricted the growth of high grasses and created a good environment for the growth of short sedges. The niche overlaps between S. aliena and S. purpurea, and P. kansuensis and P. alaschanica were relatively narrow (0.500, 0.572), which could be seen as the results of resource utilization differentiation between plant species. The species with grater niche breadth generally had greater niche overlap with other species, while the species distributed on the two extremeness of the grazing gradient had narrower niche overlap with each other, suggesting that the distribution of the species was both continuous and discontinuous.

Key words: Nutrient distribution, Eutrophication, East China Sea, Red tide