Effect of Introducing Biennial Legume Species,Melilotus officinalis,on Plant Community in the Early Stage of Vegetation Succession and Soil Nutrients in the Semiarid Loess Plateau of China Effects of Stocking Rates for Yak on Community Composition and Plant Diversity in Kobresia parva Alpine Meadow Warm-season Pasture Effects of interspecific trait dissimilarity and species evenness on the relationship between species diversity and functional diversity in an alpine meadow