The Levins niche breadth and Pianka niche overlap indices were used to assess the response of plant population niches to grazing,burning and fertilization in permanently fenced grassland of the Loess Plateau re-gion.Species with highest niche width in fenced (control group),grazed,burned and fertilized grasslands were Carex rigesaens ,Ixeridium chinense ,Artemisia sacrorum ,and Stipa bungeana ,respectively.The niche breadth of S .bungeana in different disturbance situations (ranked highest to lowest)was:fertilization (1.362)>burning (1.244)>fencing (1.088 )>grazing (1.026 ).The richness index for the same four treatments ranked:grazing>fertilization>burning>fencing.The average values of niche overlap of all the species and dominant species ranked:fertilization>fencing>burning>grazing.The pairs of species with the highest niche overlap in fertilized,fenced,burned,and grazed grasslands were,respectively,S .bungeana and C.rigesaens , Stipa grandis and C.rigesaens ,S .grandis and C.rigesaens ,and I .chinense and Poa sphondylodes ,respec-tively.These findings indicate that human disturbance can increase the species richness and improve plant pop-ulation niche width to facilitate maximum resource use in permanently fenced grassland.%运用 Levins 生态位宽度指数和 Pianka 生态位重叠指数及物种丰富度，初步分析了长期封育草地优势种群生态位对放牧、火烧和施肥的响应特征。结果表明：在封育（对照组）、放牧、火烧和施肥干扰下，生态位宽度最大的物种依次是白颖苔草、中华小苦荬、白莲蒿和本氏针茅；建群种本氏针茅在不同干扰下生态位宽度表现为施肥（1．362）＞火烧（1．244）＞封育（1．088）＞放牧（1．026），物种丰富度指数则依次为放牧＞施肥＞火烧＞封育。所有物种和优势种的生态位重叠指数平均值均表现为施肥＞封育＞火烧＞放牧，且在各干扰下，生态位重叠指数最大的种对依次为本氏针茅和白颖苔草、大针茅和白颖苔草、大针茅和白颖苔草以及中华小苦荬和硬质早熟禾。综上所述，对长期封育的草地进行适度的干扰可提高物种丰富度，改善种群的生态位配置和最大限度地利用环境资源。
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