中文摘要：

采用样方法对宁夏盐池不同年限天然草场进行调查,并计算该区植被Levins生态位宽度指数、生态位总宽度指数及Pianka生态位重叠指数,以期了解该区天然草场健康状态及植被群落的演替状况。结果表明：降雨的多少直接决定了半干旱区天然草场平均生态位宽度的大小,在研究初期生态位宽度值排在前列的主要是丝叶山苦荬（Lxeris chinensis var.graminifolia（Ledeb.）H.C.Fu）、猫头刺（Oxytropis aciphylla Ledeb）、赖草（Leymus seca-linus（Georgi）Tzvel.）;中期则为新疆猪毛菜（Salsola sinkiangensis A.J.Li）〉猫头刺〉老瓜头（Cynanchum kom-arovii Al.）;末期生态位宽度值排在前列的依次是阿尔泰狗娃花（Heteropappus altaicus（Willd.）Novopokr.）〉丝叶山苦荬〉老瓜头。天然草场在群落演替过程中是以远志（Polygala tenuifolia Willd.）和老瓜头等主要物种为稳定演替物种,伴随着丝叶山苦荬和猫头刺等物种的衰落,以及达乌里胡枝子（Lespedeza davurica（Laxm.）Schindl.）和阿尔泰狗娃花的兴起。研究中期由于降雨量的减少导致天然草场自身状态最差,但随着年限的延长,天然草场植被群落在演替过程中生态位发生分化,草场逐渐实现自我优化。

英文摘要：

Different growth periods of natural pasture in Yanchi of Ningxia province are investigated by sampling method.Levins niche breadth index,total niche breadth index and Pianka niche overlap index are calculated to study the health status of natural pasture and vegetation community succession.Results show that the niche breadth of Lxeris chinensis var.graminifolia（Ledeb.） H.C.Fu,Oxytropis aciphylla Ledeb and Leymus secalinus（Georgi） Tzvel have greater values compared with others at preliminary stage.Salsola sinkiangensis A.J.Li has the largest value of niche breadth at medium-term,followed by Oxytropis aciphylla Ledeb and Cynanchum komarovii Al.The values of niche breadth are ranked as Heteropappus altaicus（Willd.） NovopokrLxeris chinensis var.graminifolia（Ledeb.） H.C.FuCynanchum komarovii Al at the last stage.Stable succession species of natural pasture are Polygala tenuifolia Willd.and Cynanchum komarovii Al.Natural pasture shows weak condition at medium-term,However,it can achieve self-optimization gradually with ecological niche changing as growth year＇s increasing.